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Versions: 00 01 RFC 2828

Internet Engineering Task Force                                R. Shirey
INTERNET-DRAFT                                    GTE / BBN Technologies
Expiration Date: 17 April 2000                           17 October 1999


                       Internet Security Glossary
                <draft-shirey-security-glossary-01.txt>


Status of this Memo

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   all provisions of section 10 of RFC 2026 *except* that the right to
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Copyright Notice

   Copyright (C) GTE / BBN Technologies (1999). All Rights Reserved.

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   (If and when this document is issued as an RFC, we expect this
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Abstract

   This Glossary provides definitions, abbreviations, explanations, and
   recommendations for use of information system security terminology.
   The intent of the Glossary is to improve the comprehensibility of
   Internet Standards Process [R2026] documents (ISPDs). To be clear and
   understandable, ISPDs should use the same term or definition whenever


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   and wherever the same concept is mentioned. To improve international
   understanding, ISPDs should use terms in their plainest, dictionary
   sense. ISPDs should use terms established in standards documents and
   other well-founded publications and should avoid substituting private
   or newly made-up terms. ISPDs should avoid terms that are proprietary
   or otherwise favor a particular vendor, or that create a bias toward
   a particular security technology or mechanism versus other, competing
   techniques that already exist or might be developed in the future.

Table of Contents

   Section                                                          Page
   -------                                                          ----
   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2. Explanation of Paragraph Markings  . . . . . . . . . . . . . .   4
      2.1 Recommended Terms with an Internet Basis ("I") . . . . . .   4
      2.2 Recommended Terms with a Non-Internet Basis ("N")  . . . .   5
      2.3 Other Definitions ("O")  . . . . . . . . . . . . . . . . .   5
      2.4 Deprecated Terms, Definitions, and Uses ("D")  . . . . . .   6
      2.5 Commentary and Additional Guidance ("C") . . . . . . . . .   6
   3. Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 179
   5. Security Considerations  . . . . . . . . . . . . . . . . . . . 191
   6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 191
   7. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 191
   8. Expiration Date  . . . . . . . . . . . . . . . . . . . . . . . 191




























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1. Introduction

   This Glossary seeks to improve the comprehensibility of Internet
   Standards Process [R2026] documents (ISPDs)--i.e., RFCs and Internet-
   Drafts--by providing a consistent, self-supporting set of
   definitions, abbreviations, explanations, and recommendations for use
   of terminology related to information system security. A few non-
   security, networking terms are included to make the Glossary self-
   contained, but more complete glossaries of networking terms are
   available elsewhere [R1208, R1983]. There are other glossaries of
   computing terminology (including an extensive listing of hacker
   jargon [Raym]) that list additional terms that apply to Internet
   security. However, many of those terms are not appropriate for
   standards documents and, thus, have not been included in this
   dictionary.

   To provide guidance for ISPDs, this Glossary marks term and
   definitions as either endorsed or deprecated for use. The key words
   "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119. (The key words "MUST", "MUST NOT", "SHALL", and "SHALL NOT" are
   not used in this Glossary.)

   This Glossary supports the goals of the Internet Standards Process:

    o Clear, Concise, and Easily Understood Documentation

      This Glossary seeks to improve comprehensibility of security-
      related content of ISPDs. That requires the wording to be clear
      and understandable, and requires the set of security-related terms
      and definitions to be consistent and self-supporting. Also, the
      terminology needs to be uniform and across all ISPDs; the same
      term or definition needs to be used whenever and wherever the same
      concept is mentioned. Harmonization of existing ISPDs need not be
      done immediately, but is desirable to do when new versions are
      issued in the normal course of standards development and
      evolution.

    o Technical Excellence

      Just as Internet Standard protocols should operate effectively,
      ISPDs should use terminology accurately, precisely, and
      unambiguously to enable them to be implemented correctly.

    o Prior Implementation and Testing

      Just as Internet Standard protocols require experience and
      stability before adoption, ISPDs need to use well-established
      language. Using terms in their plainest, dictionary sense (when
      appropriate) help to ensure international understanding. ISPDs
      need to avoid using private, made-up terms in place of generally-
      accepted terms from standards and other publications. ISPDs need


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      to avoid substituting new definitions that conflict with
      established ones. ISPDs need to avoid using "cute" synonyms (e.g.,
      see: Green Book); no matter how popular a nickname may be in one
      community, it is likely to cause confusion in another.

    o Openness, Fairness, and Timeliness

      ISPDs need to avoid terms that are proprietary or otherwise favor
      a particular vendor, or that create a bias toward a particular
      security technology or mechanism over other, competing techniques
      that already exist or might be developed in the future. The set of
      terminology used across the set of ISPDs needs to be flexible and
      adaptable as the state of Internet security art evolves.

2. Explanation of Paragraph Markings

   Section 3 marks terms and definitions as follows:

    o Capitalization: Only terms that are proper nouns are capitalized.

    o Paragraph Marking: Definitions and explanations are stated in
   paragraphs that are marked as follows:

       - "I" identifies a RECOMMENDED Internet definition.
       - "N" identifies a RECOMMENDED non-Internet definition.
       - "O" identifies a definition that is not recommended as the
         first choice for Internet documents but is something that
         authors of Internet documents need to know.
       - "D" identifies a term or definition that SHOULD NOT be used in
         Internet documents.
       - "C" identifies commentary or additional usage guidance,
         including identifying deprecated terms.

   The rest of Section 2 further explains those four markings.

2.1 Recommended Terms with an Internet Basis ("I")

   The paragraph marking "I" (as opposed to "O") indicates a definition
   that SHOULD be the first choice for use in ISPDs. Most terms and
   definitions of this type MAY be used in ISPDs; however, some "I"
   definitions are accompanied by a "D" paragraph that recommends
   against use of the term. Also, some "I" definitions are preceded by
   an indication of a contextual usage limitation (e.g., see:
   certification), and ISPDs should not the term and definition outside
   that context

   An "I" (as opposed to an "N") also indicates that the definition has
   an Internet basis. That is, either the Internet Standards Process is
   authoritative for the term, or the term is sufficiently generic that
   the Directorate can freely state a definition without contradicting a
   non-Internet authority (e.g., see: attack).



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   Many terms with "I" definitions are proper nouns (e.g., see: Internet
   Protocol). For these terms, the "I" definition is intended only to
   provide basic information; the authoritative definition is found
   elsewhere.

   For a proper noun identified as an "Internet protocol", please refer
   to the current edition of the "Internet Official Protocol Standards"
   (STD 1) for the standardization state and status of the protocol.

2.2 Recommended Terms with a Non-Internet Basis ("N")

   The paragraph marking "N" (as opposed to "O") indicates a definition
   that the Directorate recommends SHOULD be the first choice for the
   term, if the term is used at all in Internet documents. Terms and
   definitions of this type MAY be used in Internet documents (e.g.,
   see: X.509 public-key certificate).

   However, an "N" (as opposed to an "I") also indicates a definition
   that has a non-Internet basis or origin; that is, the Internet
   Standards Process is not authoritative for the definition. Many such
   definitions are preceded by an indication of a contextual usage
   limitation, and the Directorate's endorsement does not apply outside
   that context. Also, some contexts are rarely if ever expected to
   occur in a Internet document (e.g., see: baggage). In those cases,
   the listing exists to make Internet authors aware of the non-Internet
   usage so that they can avoid conflicts with non-Internet documents.

   Many terms with "N" definitions are proper nouns (e.g., see: Computer
   Security Objects Register). For these terms, the "N" definition is
   intended only to provide basic information; the authoritative
   definition is found elsewhere.

2.3 Other Definitions ("O")

   The paragraph marking "O" (as opposed to "D") indicates a definition
   that has a non-Internet basis or origin and also indicates that the
   Directorate recommends that the definition SHOULD NOT be used in
   Internet documents *except* in cases where the term is specifically
   identified as non-Internet.

   For example, an ISPD might mention "BCA" (see: brand certification
   authority) or "baggage" as an example to illustrate some concept; in
   that case, the document should specifically say "SET(trademark) BCA"
   or "SET(trademark) baggage" and state the definition of the term.

   For some terms that have a definition published by a non-Internet
   authority--government (see: object reuse), industry (see: Secure Data
   Exchange), national (see: key authentication), or international (see:
   data confidentiality)--this Glossary marks the definition "N",
   recommending its use in Internet documents. In other cases, an
   available non-Internet definitions is inadequate or inappropriate for
   ISPDs. For example, it may be narrow or outdated, or it may need


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   clarification by substituting more careful wording or more
   explanatory wording, based on other terms that are defined here. In
   those cases, this Glossary provides an "I" definition (or sometimes a
   different "N" definition), which precedes and supersedes the
   definition marked "O".

   In cases where this Glossary provides a definition to supersede one
   that is some kind of standard, the substitute is intended to subsume
   the meaning of the "O" definition and not conflict with it. For
   "security service", for example, the "O" definition deals narrowly
   with only communication services provided by layers in the OSI model
   and is inadequate for the full range of ISPD usage; the "I"
   definition can be used in more situations and for more kinds of
   service. However, the "O" definition is provided to make authors of
   ISPDs aware of situations in which the term is used narrowly.

   This Glossary attempts to substitute understandable English that does
   not contradict any non-Internet authority. Still, terminology differs
   between the standards of the American Bar Association, OSI, SET, the
   U.S. Department of Defense, and other authorities, and this Glossary
   probably is not exactly aligned with all of them.

2.4 Deprecated Terms, Definitions, and Uses ("D")

   If the Directorate recommends that a term or definition SHOULD NOT be
   used, or SHOULD NOT be used in a certain way, in ISPDs, then either
   the definition has the paragraph marking "D", or an additional "D"
   paragraph states that restriction. Usually, a rationale is given for
   the negative recommendation (e.g., see: Green Book).

2.5 Commentary and Additional Guidance ("C")

   The paragraph marking "C" identifies text that is advisory or
   tutorial. This text MAY be reused in other Internet documents. This
   text is not intended to be authoritative, but is provided to clarify
   the definitions and to enhance this Glossary so that Internet
   security novices can use it as a tutorial.

















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3. Definitions

   ---------------------------------------------------------------------
   Note: Any acronym or other abbreviation (excluding items of common
   English usage, such as e.g., i.e., vol., pp., etc.) that is used in
   this Glossary, either in a definition or as a subpart of a defined
   term, is also defined in this Glossary.
   ---------------------------------------------------------------------

   $ 3DES
      See: triple DES.

   $ *-property
      (I) (Pronounced "star property".) See: "confinement property"
      under Bell-LaPadula Model.

   $ ABA Guidelines
      (N) "American Bar Association (ABA) Digital Signature Guidelines"
      [ABA], a framework of legal principles for using digital
      signatures and digital certificates in electronic commerce.

   $ Abstract Syntax Notation One (ASN.1)
      (N) A standard for describing data objects [X680].

      (C) OSI standards use ASN.1 to specify data formats for protocols.
      OSI defines functionality in layers, and information objects at
      higher layers are abstractly defined to be implemented with
      objects at lower layers. A higher layer may define transfers of
      abstract objects between computers, and a lower layer may define
      transfers concretely as strings of bits. Syntax is needed to
      define abstract objects, and encoding rules (see: Basic Encoding
      Rules) are needed to transform between abstract objects and bit
      strings.

      (C) In ASN.1, formal names are written without spaces, and
      separate words in a name are indicated by capitalizing the first
      letter of each word except the first word. For example, the name
      of a CRL is "certificateRevocationList".

   $ ACC
      See: access control center.

   $ access
      (I) The ability and means to communicate with or otherwise
      interact with a system in order to use system resources to either
      handle information or gain knowledge of the information the system
      contains.

      (O) "A specific type of interaction between a subject and an
      object that results in the flow of information from one to the
      other." [NCS04]



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      (C) In this Glossary, "access" is intended to cover any ability to
      communicate with a system, including one-way communication in
      either direction. In actual practice, however, entities outside a
      security perimeter that can receive output from the system but
      cannot provide input or otherwise directly interact with the
      system, might be treated as not having "access" and, therefore, be
      exempt from security policy requirements, such as the need for a
      security clearance.

   $ access control
      (I) Protection of system resources against unauthorized access; a
      process by which use of system resources is regulated according to
      a security policy and is permitted by only authorized entities
      (users, programs, processes, or other systems) according to that
      policy. (See: access, access control service.)

      (O) "The prevention of unauthorized use of a resource, including
      the prevention of use of a resource in an unauthorized manner."
      [I7498 Part 2]

   $ access control center (ACC)
      (I) A computer containing a database with entries that define a
      security policy for an access control service.

      (C) An ACC is sometimes used in conjunction with a key center to
      implement access control in a key distribution system for
      symmetric cryptography.

   $ access control list (ACL)
      (I) A mechanism that implements access control for a system
      resource by enumerating the identities of the system entities that
      are permitted to access the resource. (Compare with: capability.)

   $ access control service
      (I) A security service that protects against a system entity using
      a system resource in a way not authorized by the system's security
      policy; in short, protection of system resources against
      unauthorized access. (See: access control, discretionary access
      control, identity-based security policy, mandatory access control,
      rule-based security policy.)

      (C) This service includes protecting against use of a resource in
      an unauthorized manner by an entity that is authorized to use the
      resource in some other manner.

   $ access mode
      (I) A distinct type of data processing operation--such as read,
      write, append, or execute--that potentially can be performed on an
      object in a computer system.

   $ accountability
      (I) The property of a system (including all of its system


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      resources) that ensures that the actions of a system entity may be
      traced uniquely to that entity, which can be held responsible for
      its actions. (See: audit service.)

      (C) Accountability permits detection and subsequent investigation
      of security breaches.

   $ accredit
   $ accreditation
      (I) An administrative declaration (usually based on a technical
      certification of system security mechanisms) by a designated
      authority that an information system is approved to operate in a
      particular security configuration with a prescribed set of
      safeguards. [FP102] (See: certification.)

      (C) The terms "certification" and "accreditation" are used more in
      the U.S. Department of Defense and other government agencies than
      in commercial organizations. However, the concepts apply any place
      where managers are required to deal with and accept responsibility
      for security risks, and the American Bar Association is developing
      accreditation criteria specifically for CAs.

   $ ACL
      See: access control list.

   $ acquirer
      (N) SET usage: "The financial institution that establishes an
      account with a merchant and processes payment card authorizations
      and payments." [SET1]

      (O) "The institution (or its agent) that acquires from the card
      acceptor the financial data relating to the transaction and
      initiates that data into an interchange system." [SET2, ANSI X9.8
      and X9.24]

   $ active attack
      See: (secondary definition in) attack.

   $ active wiretapping
      See: (secondary definition in) wiretapping.

   $ add-on security
      (I) "The retrofitting of protection mechanisms, implemented by
      hardware or software, after the [automatic data processing] system
      has become operational." [FP039]

   $ administrative security
      (I) Management procedures and constraints to prevent unauthorized
      access to a system. (See: security architecture.)

      (O) "The management constraints, operational procedures,
      accountability procedures, and supplemental controls established


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      to provide an acceptable level of protection for sensitive data."
      [FP039]

      (C) Examples include clear delineation and separation of duties,
      and configuration control.

   $ Advanced Encryption Standard (AES)
      (N) A future FIPS publication being developed by NIST to succeed
      DES. Intended to specify an unclassified, publicly-disclosed,
      symmetric encryption algorithm, available royalty-free worldwide.

   $ adversary
      (I) An entity that attacks, or is a threat to, a system.

   $ Affirm
      (I) A circumstance in which a collection of information items is
      required to be classified at a higher security level than any of
      the individual items that comprise it.

   $ aggregation
      (I) A circumstance in which a collection of information items is
      required to be classified at a higher security level than any of
      the individual items that comprise it.

   $ AH
      See: Authentication Header

   $ alias
      (I) A name that an entity uses in place of its real name, usually
      for the purpose of either anonymity or deception.

   $ algorithm
      (I) A finite set of step-by-step instructions for a problem-
      solving or computation procedure, especially one that can be
      implemented by a computer. (See: cryptographic algorithm.)

   $ American National Standards Institute (ANSI)
      (N) A private, not-for-profit association of users, manufacturers,
      and other organizations, that administers U.S. private sector
      voluntary standards.

      (C) ANSI is the sole U.S. representative to the two major non-
      treaty international standards organizations, ISO and, via the
      U.S. National Committee (USNC), the International Electrotechnical
      Commission (IEC).

   $ anonymous
      (I) The condition of having a name that is unknown or concealed.
      (Compare with: anonymous login.)

      (C) An application may require security services that maintain
      anonymity of users or other system entities, perhaps to preserve


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      their privacy or shield them from attack. To hide an entity's real
      name, an alias may be used. For example, a financial institution
      may assign an account number. Parties to a transaction can thus
      remain relatively anonymous, but can also accept the transaction
      as legitimate. Real names of the parties cannot be easily
      determined by observers of the transaction, but an authorized
      third party may be able to map an alias to a real name, such as by
      presenting the institution with a court order. In other
      applications, anonymous entities may be completely untraceable.

   $ anonymous login
      (I) An access control feature (or, rather, an access control hole)
      in many Internet hosts that enables users to gain access to
      general-purpose or public services and resources on a host (such
      as allowing any user to transfer data using File Transfer
      Protocol) without having a pre-established, user-specific account
      (i.e., user name and password).

      (C) The user logs in using a special, publicly known user name
      (such as "anonymous", "guest", or "ftp") and then either is not
      asked for a password or is asked to provide a special, publicly
      known password (such as RanonymousS) or provide an arbitrary e-
      mail address as password. The user then has access to a set of
      publicly accessible system resources. This feature exposes a
      system to more threats than when all the users are pre-registered,
      trusted entities, and, of course, no individual accountability is
      possible.

   $ APOP
      See: POP3 APOP.

   $ archive
   $ archive management
      (I) (1.) Noun: A collection of data that is stored for a
      relatively long period of time for historical and other purposes,
      such as to support audit service, availability service, or system
      integrity service. (Compare with: backup.) (2.) Verb: To store
      data in such a way. (Compare with: back up.)

      (C) A digital signature may need to be verified many years after
      the signing occurs. The CA--the one that issued the certificate
      containing the public key needed to verify that signature--may not
      stay in operation that long. So every CA needs to provide for
      long-term storage of the information needed to verify the
      signatures of those to whom it issues certificates.

   $ ARPANET
      (N) Advanced Research Projects Agency Network, a pioneer packet-
      switched network that was built in the early 1970s under contract
      to the U.S. Government led to the development of today's Internet,
      and was decommissioned in June 1990.



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   $ ASN.1
      See: Abstract Syntax Notation One.

   $ association
      (I) A cooperative relationship between system entities, usually
      for the purpose of transferring information between them. (See:
      security association.)

   $ assurance
      (I) (1.) An attribute of an information system that provides
      grounds for having confidence that the system operates such that
      the system security policy is enforced. (2.) A procedure that
      ensures a system is developed and operated as intended by the
      system's security policy.

   $ assurance level
      (I) Evaluation usage: A specific level on a hierarchical scale
      representing successively increased confidence that a target of
      evaluation adequately fulfills the requirements (e.g., see:
      TCSEC).

   $ asymmetric cryptography
      (I) A modern branch of cryptography (popularly known as "public-
      key cryptography") in which the algorithms employ a pair of keys
      (a public key and a private key) and use a different component of
      the pair for different steps of the algorithm. (See: key pair.)

      (C) Asymmetric algorithms have key management advantages over
      equivalently strong symmetric ones. First, one key of the pair
      does not need to be known by anyone but its owner; so it can more
      easily be kept secret. Second, although the other key of the pair
      is shared by all entities that use the algorithm, that key does
      not need to be kept secret from other, non-using entities; so the
      key distribution part of key management can be done more easily.

      (C) For encryption: In an asymmetric encryption algorithm (e.g.,
      see: RSA), when Alice wants to ensure confidentiality for data she
      sends to Bob, she encrypts the information with a public key
      provided by Bob. Only Bob has the matching private key that is
      needed to decrypt the data.

      (C) For signature: In an asymmetric digital signature algorithm
      (e.g., see: DSA), when Alice wants to ensure data integrity or
      provide authentication for data she sends to Bob, she uses her
      private key to sign (create a digital signature from) the data. To
      verify the signature, Bob uses the matching public key that Alice
      has provided.

      (C) For key agreement: In an asymmetric key agreement algorithm
      (e.g., see: Diffie-Hellman), Alice and Bob each send their own
      public key to the other person. Then each uses their own private
      key and the other's public key to compute the new key value.


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   $ attack
      (I) An assault on system security that derives from an intelligent
      threat, i.e., an intelligent act that is a deliberate attempt
      (especially in the sense of a method or approach) to evade
      security services and violate the security policy of a system.
      (See: penetration, violation, vulnerability.)

       - Active vs. passive: An "active attack" attempts to alter system
         resources or affect their operation. A "passive attack"
         attempts to learn or make use of information (e.g., see:
         wiretapping) does not affect system resources.

       - Insider vs. outsider: An "inside attack" is an attack initiated
         by an entity inside the security perimeter (an "insider"),
         i.e., by an entity that is authorized to access system
         resources but uses them in a way not approved by those who
         granted the authorization. An "outside attack" is initiated
         from outside the perimeter, by an unauthorized or illegitimate
         user of the system (an "outsider"). In the Internet, potential
         outside attackers range from amateur pranksters to organized
         criminals, international terrorists, and hostile governments.

      (C) The term "attack" relates to some other basic security terms
      as shown in the following model:

      + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+
      | An Attack:              |  |Counter- |  | A System Resource:   |
      | i.e., A Threat Action   |  | measure |  | Target of the Attack |
      | +----------+            |  |         |  | +-----------------+  |
      | | Attacker |<==================||<=========                 |  |
      | |   i.e.,  |   Passive  |  |         |  | |  Vulnerability  |  |
      | | A Threat |<=================>||<========>                 |  |
      | |  Agent   |  or Active |  |         |  | +-------|||-------+  |
      | +----------+   Attack   |  |         |  |         VVV          |
      |                         |  |         |  | Threat Consequences  |
      + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+

   $ attribute authority
      (I) A CA that issues attribute certificates.

      (O) "An authority, trusted by the verifier to delegate privilege,
      which issues attribute certificates." [FPDAM]

   $ attribute certificate
      (I) A digital certificate that binds a set of descriptive data
      items, other than a public key, either directly to a subject name
      or to the identifier of another certificate that is a public-key
      certificate. [X509]

      (O) "A set of attributes of a user together with some other
      information, rendered unforgeable by the digital signature created


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      using the private key of the CA which issued it." [X509]

      (O) "A data structure that includes some attribute values and
      identification information about the owner of the attribute
      certificate, all digitally signed by an Attribute Authority. This
      authority's signature serves as the guarantee of the binding
      between the attributes and their owner." [FPDAM]

      (C) A public-key certificate binds a subject name to a public key
      value, along with information needed to perform certain
      cryptographic functions. Other attributes of a subject, such as a
      security clearance, may be certified in a separate kind of digital
      certificate, called an attribute certificate. A subject may have
      multiple attribute certificates associated with its name or with
      each of its public-key certificates.

      (C) An attribute certificate might be issued to a subject in the
      following situations:

       - Different lifetimes: When the lifetime of an attribute binding
         is shorter than that of the related public-key certificate, or
         when it is desirable not to need to revoke a subject's public
         key just to revoke an attribute.

       - Different authorities: When the authority responsible for the
         attributes is different than the one that issues the public-key
         certificate for the subject. (There is no requirement that an
         attribute certificate be issued by the same CA that issues the
         associated public-key certificate.)

   $ audit service
      (I) A security service that records information needed to
      establish accountability for system events and the actions of
      system entities that cause them. (See: security audit.)

   $ audit trail
      See: security audit trail.

   $ authentic signature
      (I) A signature (particularly a digital signature) that can be
      trusted because it can be verified. (See: validate vs. verify.)

   $ AUTH
      See: POP3 AUTH.

   $ authenticate
      (I) Verify (i.e., establish the truth of) an identity claimed by
      or for a system entity. (See: authentication.)

      (C) This definition is narrower than in general English usage,
      where this term usually means "to prove genuine"; for example, an
      art expert authenticates a Michelangelo painting.


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      (D) Although we might be tempted to speak similarly of
      authenticating a digital signature or digital certificate, ISPDs
      SHOULD NOT use that language in the context of asymmetric
      cryptography. Instead, we "sign" and then "verify" digital
      signatures, and we "issue" and then "validate" digital
      certificates. (See: validate vs. verify.)

   $ authentication
      (I) The process of verifying an identity claimed by or for a
      system entity. (See: authentication exchange, authentication
      information, data origin authentication, peer entity
      authentication.)

      (C) An authentication process consists of two steps:

       - Identification step: Presenting an identifier to the security
         system. (Identifiers should be assigned carefully, because
         authenticated identities are the basis for other security
         services, such as access control service.)

       - Verification step: Presenting or generating authentication
         information that corroborates the binding between the entity
         and the identifier. (See: verification.)

      (C) See: ("relationship between data integrity service and
      authentication services" in) data integrity service.

   $ authentication code
      (D) ISPDs SHOULD NOT use this term because it is sometimes
      misleading defined as a synonym for cryptographic checksum. The
      word "authentication" is misleading because the mechanism involved
      usually serves a data integrity function rather than an
      authentication function. (See: message authentication code.)

   $ Authentication Header (AH)
      (I) An Internet IPsec protocol [R2402] designed to provide
      connectionless data integrity service and data origin
      authentication service for IP datagrams, and (optionally) to
      provide protection against replay attacks.

      (C) Replay protection may be selected by the receiver when a
      security association is established. AH authenticates upper-layer
      protocol data units and as much of the IP header as possible.
      However, some IP header fields may change in transit, and the
      value of these fields, when the packet arrives at the receiver,
      may not be predictable by the sender. The values of such fields
      cannot be protected by AH. Thus, protection of the IP header by AH
      is only partial.

      (C) AH may be used alone, or in combination with the IPsec ESP
      protocol, or in a nested fashion with tunneling. Security services


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      can be provided between a pair of communicating hosts, between a
      pair of communicating security gateways, or between a host and a
      gateway. ESP can provide the same security services as AH, and ESP
      can also provide data confidentiality service. The main difference
      between authentication services provided by ESP and AH is the
      extent of the coverage; ESP does not protect IP header fields
      unless they are encapsulated by AH.

   $ authentication exchange
      (I) A mechanism to verify the identity of an entity by means of
      information exchange.

      (O) "A mechanism intended to ensure the identity of an entity by
      means of information exchange." [I7498 Part 2]

   $ authentication information
      (I) Information used to verify an identity claimed by or for an
      entity. (See: authentication, credential.)

      (C) Authentication information may exist as, or be derived from,
      one of the following:

       - Something the entity knows. (See: password).
       - Something the entity possesses. (See: token.)
       - Something the entity is. (See: biometric authentication.)

   $ authentication service
      (I) A security service that verifies an identity claimed by or for
      an entity. (See: authentication.)

      (C) In a network, there are two general forms of authentication
      service: data origin authentication service and peer entity
      authentication service.

   $ authenticity
      (I) The property of being genuine and able to be verified and be
      trusted. (See: authenticate, authentication, validate vs. verify)

   $ authority
      (D) "An entity, responsible for the issuance of certificates."
      [FPDAM]

      (C) ISPDs SHOULD NOT use this term as a synonym for either AA, CA,
      RA, ORA, or similar terms, because it may cause confusion.
      Instead, if it is necessary to shorten text, use abbreviations
      defined in this Glossary.

      (C) ISPDs SHOULD NOT use this definition for any PKI entity,
      because the definition is ambiguous with regard to whether the
      entity actually issues certificates (see: attribute authority,
      certification authority) or just has responsibility for part of
      the processes that precede or follow issuance (see: registration


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      authority). (See: issue.)

   $ authority certificate
      (D) "A certificate issued to an authority (e.g. either to a
      certification authority or to an attribute authority)." [FPDAM]
      (See: authority.)

      (C) ISPDs SHOULD NOT use this term or definition because they are
      with regard to which specific types of PKI entities they address.

   $ authority revocation list (ARL)
      (I) A data structure that enumerates digital certificates that
      were issued to certification authorities but have been invalidated
      by their issuer prior to when they were scheduled to expire (see:
      certificate expiration). (See: X.509 authority revocation list.)

      (O) "A revocation list containing a list of public-key
      certificates issued to authorities, which are no longer considered
      valid by the certificate issuer." [FPDAM]

   $ authorize
   $ authorization
      (I) (1.) To "authorize" means to grant a right or permission to a
      system entity to access a system resource. (2.) An "authorization"
      is a right or a permission that is granted. (See: privilege.) (3.)
      An "authorization process" is a procedure for granting such
      rights.

      (O) SET usage: "The process by which a properly appointed person
      or persons grants permission to perform some action on behalf of
      an organization. This process assesses transaction risk, confirms
      that a given transaction does not raise the account holder's debt
      above the account's credit limit, and reserves the specified
      amount of credit. (When a merchant obtains authorization, payment
      for the authorized amount is guaranteed--provided, of course, that
      the merchant followed the rules associated with the authorization
      process.)" [SET2]

   $ automated information system
      (I) An organized assembly of resources and procedures--i.e.,
      computing and communications equipment and services, with their
      supporting facilities and personnel--that collect, record,
      process, store, transport, retrieve, or display information to
      accomplish a specified set of functions.

   $ availability
      (I) The property of a system or a system resource being accessible
      and usable upon demand by an authorized system entity, according
      to performance specifications for the system; i.e., a system is
      available if it provides services according to the system design
      whenever users request them. (See: critical, denial of service,
      reliability, survivability.)


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      (O) "The property of being accessible and usable upon demand by an
      authorized entity." [I7498 Part 2]

   $ availability service
      (I) A security service that protects a system to ensure its
      availability.

      (C) This service addresses the security concerns raised by denial-
      of-service attacks. It depends on proper management and control of
      system resources, and thus depends on access control service and
      other security services.

   $ back door
      (I) A hardware or software mechanism that (a) provides access to a
      system and its resources by other than the usual procedure, (b)
      was  deliberately left in place by the system's designers or
      maintainers, and (c) usually is not publicly known. (See: trap
      door.)

      (C) For example, a way to access a computer other than through the
      legitimate login procedure. Such security holes do not necessarily
      have malicious intent; e.g., operating systems sometimes are
      shipped by the manufacturer with privileged accounts intended for
      use by field service technicians or the vendor's maintenance
      programmers. (See: trap door.)

   $ back up vs. backup
      (I) Verb "back up": To store data for the purpose of creating a
      backup copy. (Compare with: archive.)

      (I) Noun/adjective "backup": (1.) A reserve copy of data that is
      stored separately from the original, for use if the original
      becomes lost or damaged. (Compare with: archive.) (2.) Alternate
      means to permit performance of system functions despite a disaster
      to system resources. (See: contingency plan.)

   $ baggage
      (D) ISPDs SHOULD NOT use this term to describe a data element
      except when stated as "SET(trademark) baggage" with the following
      meaning:

      (O) SET usage: An "opaque encrypted tuple, which is included in a
      SET message but appended as external data to the PKCS encapsulated
      data. This avoids superencryption of the previously encrypted
      tuple, but guarantees linkage with the PKCS portion of the
      message." [SET2]

   $ bandwidth
      (I) Commonly used to mean the capacity of a communication channel
      to pass data through the channel in a given amount of time.
      (Usually expressed in bits per second.)


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   $ bank identification number (BIN)
      (I) The digits of a credit card number that identify the issuing
      bank. (See: primary account number.)

      (O) SET usage: The first six digits of a primary account number.

   $ Basic Encoding Rules (BER)
      (I) A standard for representing ASN.1 data types as strings of
      octets (eight-bit values) [X690]. (See: Distinguished Encoding
      Rules.)

   $ bastion host
      (I) A strongly protected computer that is in a network protected
      by a firewall (or is part of a firewall) and is the only host (or
      one of only a few hosts) in the network that can be directly
      accessed from networks on the other side of the firewall.

      (C) Filtering routers in a firewall typically restrict traffic
      from the outside network to reaching just one host, the bastion
      host, which usually is part of the firewall. Since only this one
      host can be directly attacked, only this one host needs to be very
      strongly protected, so security can be maintained more easily and
      less expensively. However, to allow legitimate internal and
      external users to access application resources through the
      firewall, higher layer protocols and services need to be relayed
      and forwarded by the bastion host. Some services have forwarding
      built in (like DNS or SMTP); other services (like TELNET and FTP)
      require a proxy server on the bastion host.

   $ BCA
      See: brand certification authority.

   $ BCI
      See: brand CRL identifier.

   $ Bell-LaPadula Model
      (N) A formal, mathematical, state-transition model of security
      policy for multilevel-secure computer systems, devised by David
      Bell and Leonard LaPadula at The MITRE Corporation in 1973.

      (C) The model separates computer system elements into a set of
      subjects and a set of objects. To determine whether or not a
      subject is authorized for a particular access mode on an object,
      the clearance of the subject is compared to the classification of
      the object. The model defines the notion of a "secure state", in
      which the only permitted access modes of subjects to objects are
      in accordance with a specified security policy. It is proven that
      each state transition preserves security by moving from secure
      state to secure state, thereby proving that the system is secure.

      (C) In this model, a multilevel-secure system satisfies several


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      rules, including the following:

       - "Confinement property" (also called "*-property", pronounced
         "star property"): A subject has write access to an object only
         if classification of the object dominates the clearance of the
         subject.

       - "Simple security property": A subject has read access to an
         object only if the clearance of the subject dominates the
         classification of the object.

       - "Tranquillity property": The classification of an object does
         not change while the object is being processed by the system.

   $ BER
      See: Basic Encoding Rules.

   $ beyond A1
      (O) A level of trust that is beyond the highest level of criteria
      specified by the TCSEC. That is, a level of security that is so
      high as not be verifiable by currently available formal methods.

   $ BIN
      See: bank identification number.

   $ bind
      (I) To inseparably associate by applying some mechanism, such as
      when a CA uses a digital signature to bind together a subject and
      a public key in a public-key certificate.

   $ biometric authentication
      (I) A method of generating authentication information for a person
      by digitizing measurements of a physical characteristic, such as
      fingerprint patterns, hand shape, retina pattern, speech sounds,
      or handwriting pattern.

   $ bit
      (I) The smallest unit of information storage; a contraction of the
      term "binary digit"; one of two symbols--"0" (zero) and "1" (one)
      --that are used to represent binary numbers.

   $ BLACK
      (I) Designation for information system equipment or facilities
      that handle (and for data that contains) only ciphertext (or,
      depending on the context, only unclassified information), and for
      such data itself. This term derives from U.S. Government COMSEC
      terminology. (Compare with: RED. Also see: RED/BLACK separation.)

   $ block cipher
      (I) An encryption algorithm that breaks plaintext into fixed-size
      segments and uses the same key to transform each plaintext segment
      into a fixed-size segment of ciphertext. (See: mode, stream


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      cipher.)

      (C) For example, Blowfish, DEA, IDEA, RC2, and SKIPJACK. However,
      a block cipher can be adapted to have a different external
      interface, such as that of a stream cipher, by using a mode of
      operation to "package" the basic algorithm.

   $ Blowfish
      (N) A symmetric block cipher with variable-length key (32 to 448
      bits) designed in 1993 by Bruce Schneier [Schn] as an unpatented,
      license-free, royalty-free replacement for DES or IDEA.

   $ brand
      (I) A distinctive mark or name that identifies a product or
      business entity.

      (O) SET usage: The name of a payment card. Financial institutions
      and other companies have founded payment card brands, protect and
      advertise the brands, establish and enforce rules for use and
      acceptance of their payment cards, and provide networks to
      interconnect the financial institutions. These brands combine the
      roles of issuer and acquirer in interactions with cardholders and
      merchants. [SET1]

   $ brand certification authority (BCA)
      (O) SET usage: A CA owned by a payment card brand, such as
      MasterCard, Visa, or American Express. [SET2] (See: certification
      hierarchy, SET.)

   $ brand CRL identifier (BCI)
      (O) SET usage: A digitally signed list, issued by the BCA, of the
      names of CAs for which CRLs need to be processed when verifying
      signatures in SET messages. [SET2]

   $ break
      (I) Cryptographic usage: To successfully perform cryptanalysis and
      thus succeed in decrypting data or performing some other
      cryptographic function, without initially having knowledge of the
      key that the function requires. (This term applies to encrypted
      data or, more generally, to a cryptographic algorithm or
      cryptographic system.)

   $ bridge
      (I) A computer that is a gateway between two networks (usually two
      LANs) at OSI layer 2. (Compare with: router.)

   $ British Standard 7799
      (N) Part 1 is a standard code of practice and provides guidance on
      how to secure an information system; Part 2 specifies the
      management framework, objectives, and control requirements for
      information security management systems [B7799]. The certification
      scheme works like ISO 9000. It is in use in the UK, the


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      Netherlands, Australia, and New Zealand and might be proposed as
      an ISO standard or adapted to be part of the Common Criteria.


   $ browser
      (I) An client computer program that can retrieve and display
      information from servers on the World Wide Web.

      (C) For example, Netscape's Navigator and Communicator, and
      Microsoft's Explorer.

   $ brute force
      (I) A cryptanalysis approach or other kind of attack method
      involving an exhaustive procedure that tries all possibilities,
      one-by-one.

      (C) For example, for ciphertext where the analyst already knows
      the decryption algorithm, a brute force approach to finding the
      original plaintext is to decrypt the message with every possible
      key.

   $ BS7799
      See: British Standard 7799.

   $ byte
      (I) A fundamental unit of computer storage; the smallest
      addressable unit in a computer's architecture. Usually holds one
      character of information; and, today, usually means eight bits.
      (See: octet.)

      (C) Larger than a "bit", but smaller than a "word". Although
      usually eight bits today, was other sizes (e.g., six bits, nine
      bits) in earlier computer architectures.

   $ CA
      See: certification authority.

   $ CA certificate
      (I) "A [digital] certificate for one CA issued by another CA."
      [X509]

      (C) That is, a digital certificate whose holder is able to issue
      digital certificates. A v3 X.509 public-key certificate may have a
      "basicConstraints" extension containing a "cA" value that
      specifically "indicates whether or not the public key may be used
      to verify certificate signatures."

   $ call back
      (I) An authentication technique for terminals that remotely access
      a computer via telephone lines; the host system disconnects the
      caller and then calls back on a telephone number that was
      previously authorized for that terminal.


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   $ capability
      (I) A token, usually an unforgeable data value (sometimes called a
      "ticket") that gives the bearer or holder the right to access a
      system resource. Possession of the token is accepted by a system
      as proof that the holder has been authorized to access the
      resource named or indicated by the token. (Compare with: access
      control list.)

      (C) This concept can be implemented as a digital certificate.
      (See: attribute certificate.)

   $ CAPI
      See: cryptographic application programming interface.

   $ CAPSTONE chip
      (N) An integrated circuit (the Mykotronx, Inc. MYK-82) with a Type
      II cryptographic processor that implements SKIPJACK, KEA, DSA,
      SHA, and basic mathematical functions to support asymmetric
      cryptography, and includes the key escrow feature of the CLIPPER
      chip. (See: FORTEZZA card.)

   $ card
      See: cryptographic card, FORTEZZA card, payment card, PC card,
      smart card, token.

   $ card backup
      See: token backup.

   $ card copy
      See: token copy.

   $ card restore
      See: token restore.

   $ cardholder
      (I) An entity that has been issued a card.

      (O) SET usage: "The holder of a valid payment card account and
      user of software supporting electronic commerce." [SET2] A
      cardholder is issued a payment card by an issuer. SET ensures that
      in the cardholder's interactions with merchants, the payment card
      account information remains confidential. [SET1]

   $ cardholder certificate
      (O) SET usage: A digital certificate that is issued to a
      cardholder upon approval of the cardholder's issuing financial
      institution and that is transmitted to merchants with purchase
      requests and encrypted payment instructions, carrying assurance
      that the account number has been validated by the issuing
      financial institution and cannot be altered by a third party.
      [SET1]


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   $ cardholder certification authority (CCA)
      (O) SET usage: A CA responsible for issuing digital certificates
      to cardholders and operated on behalf of a payment card brand, an
      issuer, or another party according to brand rules. A CCA maintains
      relationships with card issuers to allow for the verification of
      cardholder accounts. A CCA does not issue a CRL but does
      distribute CRLs issued by root CAs, brand CAs, geopolitical CAs,
      and payment gateway CAs. [SET2]

   $ CAST
      (N) A design procedure for symmetric encryption algorithms, and a
      resulting family of algorithms, invented by C(arlisle) A(dams) and
      S(tafford) T(avares). [R2612]

   $ category
      (I) A grouping of sensitive information items to which a non-
      hierarchical restrictive security label is applied to increase
      protection of the data. (See: compartment.)

   $ CAW
      See: certification authority workstation.

   $ CBC
      See: cipher block chaining.

   $ CCA
      See: cardholder certification authority.

   $ CCITT
      (N) Acronym for French translation of International Telephone and
      Telegraph Consultative Committee. Now renamed ITU-T.

   $ CERT
      See: computer emergency response team.

   $ certificate
      (I) In common English usage, a document that attests to the truth
      of something or the ownership of something.

      (C) Security usage, see: digital certificate, X.509 certificate.

      (C) PKI usage, see: public-key certificate.

   $ certificate authority
      (D) This term looks like imprecise use of a term standardized by
      X.509 and, therefore, ISPDs SHOULD NOT use this term as a synonym
      for "certification authority".

   $ certificate chain
      (D) ISPDs SHOULD NOT use this term because it duplicates the
      meaning of a standardized term. Instead, use "certification path".


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   $ certificate chain validation
      (D) ISPDs SHOULD NOT use this term because it duplicates the
      meaning of standardized terms and mixes concepts in a potentially
      misleading way. Instead, use "certificate validation" or "path
      validation", depending on what is meant. (See: validate vs.
      verify.)

   $ certificate creation
      (I) The act or process by which a CA sets the values of a digital
      certificate's data fields and signs it. (See: issue.)

   $ certificate expiration
      (I) The event that occurs when a certificate ceases to be valid
      because its assigned lifetime has been exceeded. (See: certificate
      revocation, validity period.)

   $ certificate extension
      See: extension.

   $ certificate holder
      (I) A system entity named as the subject of a digital certificate.

   $ certificate management
      (I) The functions that a CA may perform during the life cycle of a
      digital certificate, including the following:

       - Acquire and verify data items to bind into the certificate.
       - Encode and sign the certificate.
       - Store the certificate in a directory or repository.
       - Renew, rekey, and update the certificate.
       - Revoke the certificate and issue a CRL.

      (See: archive management, key management, security architecture,
      token management, certificate management.)

   $ certificate policy
      (I) "A named set of rules that indicates the applicability of a
      certificate to a particular community and/or class of application
      with common security requirements." [X509] (Compare with:
      certification practice statement.)

      (C) A certificate policy can help a certificate user decide
      whether a certificate should be trusted in a particular
      application. "For example, a particular certificate policy might
      indicate applicability of a type of certificate for the
      authentication of electronic data interchange transactions for the
      trading goods within a given price range." [R2527]

      (C) A v3 X.509 public-key certificate may have a
      "certificatePolicies" extension that lists certificate policies,
      recognized by the issuing CA, that apply to the certificate and


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      govern its use. Each policy is denoted by an object identifier and
      may optionally have certificate policy qualifiers.

      (C) SET usage: Every SET certificate specifies at least one
      certificate policy, that of the SET root CA. SET uses certificate
      policy qualifiers to point to the actual policy statement and to
      add qualifying policies to the root policy. (See: SET qualifier.)

   $ certificate policy qualifier
      (I) Information that pertains to a certificate policy and is
      included in a "certificatePolicies" extension in a v3 X.509
      public-key certificate.

   $ certificate reactivation
      (I) The act or process by which a digital certificate, which a CA
      has designated for revocation but not yet listed on a CRL, is
      returned to the valid state.

   $ certificate rekey
      (I) The act or process by which an existing public-key certificate
      has its public key value changed by issuing a new certificate with
      a different (usually new) public key. (See: certificate renewal,
      certificate update, rekey.)

      (C) For an X.509 public-key certificate, the essence of rekey is
      that the subject stays the same and a new public key is bound to
      that subject. Other changes are made, and the old certificate is
      revoked, only as required by the PKI and CPS in support of the
      rekey. If changes go beyond that, the process is a "certificate
      update".

      (O) MISSI usage: To rekey a MISSI X.509 public-key certificate
      means that the issuing authority creates a new certificate that is
      identical to the old one, except the new one has a new, different
      KEA key; or a new, different DSS key; or new, different KEA and
      DSS keys. The new certificate also has a different serial number
      and may have a different validity period. A new key creation date
      and maximum key lifetime period are assigned to each newly
      generated key. If a new KEA key is generated, that key is assigned
      a new KMID. The old certificate remains valid until it expires,
      but may not be further renewed, rekeyed, or updated.

   $ certificate renewal
      (I) The act or process by which the validity of the data binding
      asserted by an existing public-key certificate is extended in time
      by issuing a new certificate. (See: certificate rekey, certificate
      update.)

      (C) For an X.509 public-key certificate, this term means that the
      validity period is extended but the binding of the public key to
      the subject and to other data items stays the same. The other data
      items are changed, and the old certificate is revoked, only as


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      required by the PKI and CPS to support the renewal. If changes go
      beyond that, the process is a "certificate rekey" or "certificate
      update".

   $ certificate request
      (D) ISPDs SHOULD NOT use this term because it looks like imprecise
      use of a term standardized by PKCS #10 and used in PKIX. Instead,
      use "certification request".

   $ certificate revocation
      (I) The event that occurs when a CA declares that a previously
      valid digital certificate issued by that CA has become invalid;
      usually stated with a revocation date.

      (C) In X.509, a revocation is announced to potential certificate
      users by a CRL that mentions the certificate. Revocation and
      listing on a CRL is only necessary before certificate expiration.

   $ certificate revocation list (CRL)
      (I) A data structure that enumerates digital certificates that
      have been invalidated by their issuer prior to when they were
      scheduled to expire (see: certificate expiration). (See: X.509
      certificate revocation list.)

      (O) "A signed list indicating a set of certificates that are no
      longer considered valid by the certificate issuer. After a
      certificate appears on a CRL, it is deleted from a subsequent CRL
      after the certificateUs expiry. CRLs may be used to identify
      revoked public-key certificates or attribute certificates and may
      represent revocation of certificates issued to authorities or to
      users. The term CRL is also commonly used as a generic term
      applying to all the different types of revocation lists, including
      CRLs, ARLs, ACRLs, etc." [FPDAM]

   $ certificate revocation tree
      (I) A mechanism for distributing notice of certificate revocations
      (as an alternative to issuing a CRL), using a tree of hash results
      that is signed by the tree's issuer.

   $ certificate serial number
      (I) An integer value that (1) is associated with, and may be
      carried in, a digital certificate; (2) is assigned to the
      certificate by the certificate's issuer; and (3) is unique among
      all the certificates produced by that issuer.

      (O) "An integer value, unique within the issuing CA, which is
      unambiguously associated with a certificate issued by that CA.
      [X509]

   $ certificate status responder
      (N) FPKI usage: A trusted on-line server that acts for a CA to
      provide authenticated certificate status information to


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      certificate users. [FPKI]

   $ certificate update
      (I) The act or process by which data items bound in an existing
      public-key certificate, especially authorizations granted to the
      subject, are changed by issuing a new certificate. (See:
      certificate rekey, certificate renewal.)

      (C) For an X.509 public-key certificate, the essence of this
      process is that fundamental changes are made in the data that is
      bound to the public key, such that it is necessary to revoke the
      old certificate. (Otherwise, the process is only a "certificate
      rekey" or "certificate renewal".)

   $ certificate user
      (I) A system entity that depends on the validity of information
      (such as another entity's public key value) provided by a digital
      certificate. (See: relying party.)

      (O) "An entity that needs to know, with certainty, the public key
      of another entity." [X509]

      (C) The system entity may be a human being or an organization, or
      a device or process under the control of a human or an
      organization.

      (D) ISPDs SHOULD NOT use this term as a synonym for the "subject"
      of a certificate.

   $ certificate validation
      (I) An act or process by which a certificate user establishes that
      the assertions made by a digital certificate can be trusted. (See:
      valid certificate, validate vs. verify.)

      (O) "The process of ensuring that a certificate is valid including
      possibly the construction and processing of a certification path,
      and ensuring that all certificates in that path have not expired
      or been revoked." [FPDAM]

      (C) To validate a certificate, a certificate user checks that the
      certificate is properly formed and signed and currently in force:

       - Signature: Employs the issuer's public key to verify the
         digital signature of the CA who issued the certificate in
         question. If the key is obtained from the issuer's own public-
         key certificate, that certificate also should be validated.
         That validation may lead to yet another certificate to be
         validated, and so on. Thus, in general, certificate validation
         involves discovering and validating a certification path.

       - Syntax and semantics: Parses the certificate's syntax and
         interprets its semantics, applying rules specified for and by


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         its data fields, such as for critical extensions in an X.509
         certificate.

       - Currency and revocation: Verifies that the certificate is
         currently in force by checking that the current date and time
         are within the validity period (if that is specified in the
         certificate) and that the certificate is not listed on a CRL or
         otherwise announced as in valid. (CRLs themselves require a
         similar validation process.)

   $ certification
      (I) Information system usage: Technical evaluation (usually made
      in support of an accreditation action) of an information system's
      security features and other safeguards to establish the extent to
      which the system's design and implementation meet specified
      security requirements. [FP102] (See: accreditation.)

      (I) Digital certificate usage: The act or process of vouching for
      the truth and accuracy of the binding between data items in the
      certificate. (See: certify.)

      (I) Public key usage: The act or process of vouching for the
      ownership of a public key by issuing a public-key certificate that
      binds the key to the name of the entity that owns the key. (In
      addition to binding a key with a name, a public-key certificate
      may bind those items with other restrictive or explanatory data
      items; e.g., see: X.509 public-key certificate.)

      (O) SET usage: "The process of ascertaining that a set of
      requirements or criteria has been fulfilled and attesting to that
      fact to others, usually with some written instrument. A system
      that has been inspected and evaluated as fully compliant with the
      SET protocol by duly authorized parties and process would be said
      to have been certified compliant." [SET2]

   $ certification authority (CA)
      (I) An entity that issues digital certificates (especially X.509
      certificates) and vouches for the binding between the data items
      in a certificate.

      (O) "An authority trusted by one or more users to create and
      assign certificates. Optionally the certification authority may
      create the user's keys." [X509]

      (C) Certificate users depend on the validity of information
      provided by a certificate. Thus, a CA should be someone that
      certificate users trust, and usually holds an official position
      created and granted power by a government, a corporation, or some
      other organization. A CA is responsible for managing the life
      cycle of certificates (see: certificate management) and, depending
      on the type of certificate and the CPS that applies, may be
      responsible for the life cycle of key pairs associated with the


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      certificates (see: key management).

   $ certification authority workstation (CAW)
      (I) A computer system that enables a CA to issue digital
      certificates and supports other certificate management functions
      as required.

   $ certification hierarchy
      (I) A tree-structured (loop-free) topology of relationships among
      CAs and the entities to whom the authorities issue public-key
      certificates. (See: hierarchical PKI.)

      (C) In this structure, one CA is the top CA, the highest level of
      the hierarchy. (See: root, top CA.) The top CA may issue public-
      key certificates to one or more additional CAs that form the
      second highest level. Each of these CAs may issue certificates to
      more CAs at the third highest level, and so on. The CAs at the
      bottom of the hierarchy issue certificates only to entities that
      are not CAs (see: end entity). Thus, all certification paths begin
      at the top CA and descend through one or more levels of other CAs.
      All certificate users base path validations on the top CA's public
      key.

      (O) MISSI usage: A MISSI certification hierarchy has three or four
      levels:

       - A CA at the highest level, the top CA, is a "policy approving
         authority".
       - A CA at the second-highest level is a "policy creation
         authority".
       - A CA at the third-highest level is a local authority called a
         "certification authority".
       - A CA at the fourth-highest (optional) level is a "subordinate
         certification authority".

      (O) PEM usage: A PEM certification hierarchy has three levels
      [R1422]:

       - The highest level is the "Internet Policy Registration
         Authority".
       - A CA at the second-highest level is a "policy certification
         authority".
       - A CA at the third-highest level is a "certification authority".

      (O) SET usage: A SET certification hierarchy has three or four
      levels:

       - The highest level is a "SET root CA".
       - A CA at the second-highest level is a "brand certification
         authority".
       - A CA at the third-highest (optional) level is a "geopolitical
         certification authority".


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       - A CA at the fourth-highest level is a "cardholder CA", a
         "merchant CA", or a "payment gateway CA".

   $ certification path
      (I) An ordered sequence of public-key certificates (or a sequence
      of public-key certificates followed by one attribute certificate)
      that enables a certificate user to verify the signature on the
      last certificate in the path, and thus enables the user to obtain
      a certified public key (or certified attributes) of the entity
      that is the subject of that last certificate. (See: certificate
      validation, valid certificate.)

      (O) "An ordered sequence of certificates of objects in the [X.500
      Directory Information Tree] which, together with the public key of
      the initial object in the path, can be processed to obtain that of
      the final object in the path." [X509, R2527]

      (C) The path is the "list of certificates needed to allow a
      particular user to obtain the public key of another." [X509] The
      list is "linked" in the sense that the digital signature of each
      certificate (except the first) is verified by the public key
      contained in the preceding certificate; i.e., the private key used
      to sign a certificate and the public key contained in the
      preceding certificate form a key pair owned by the entity that
      signed.

      (C) In the X.509 quotation in the previous "C" paragraph, the word
      "particular" points out that a certification path that can be
      validated by one certificate user might not be able to be
      validated by another. (See: certificate validation.) That is
      because either the first certificate should be a trusted
      certificate (it might be a root certificate) or the signature on
      the first certificate should be verified by a trusted key (it
      might be a root key), and that such trust is relative to the user.

   $ certification policy
      (D) ISPDs SHOULD NOT use this term. Instead, use either
      "certificate policy" or "certification practice statement",
      depending on what is meant.

   $ certification practice statement (CPS)
      (I) "A statement of the practices which a certification authority
      employs in issuing certificates." [ABA96, R2527] (Compare with:
      certificate policy.)

      (C) A CPS is a published security policy that can help a
      certificate user to decide whether a certificate issued by a
      particular CA can be trusted enough to use in a particular
      application. A CPS may be (a) a declaration by a CA of the details
      of the system and practices it employs in its certificate
      management operations, (b) part of a contract between the CA and
      an entity to whom a certificate is issued, (c) a statute or


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      regulation applicable to the CA, or (d) a combination of these
      types involving multiple documents. [ABA]

      (C) A CPS is usually more detailed and procedurally oriented than
      a certificate policy. A CPS applies to a particular CA or CA
      community, while a certificate policy applies across CAs or
      communities. A CA with a single CPS may support multiple
      certificate policies, which may be used for different application
      purposes or by different user communities. Multiple CAs, each with
      a different CPS, may support the same certificate policy. [R2527]

   $ certification request
      (I) A algorithm-independent transaction format, defined by PCKS
      #10 and used in PKIX, that contains a DN, a public key, and
      optionally a set of attributes, collectively signed by the entity
      requesting certification, and sent to a CA, which transforms the
      request to an X.509 public-key certificate or another type of
      certificate.

   $ certify
      1. (I) Issue a digital certificate and thus vouch for the truth,
      accuracy, and binding between data items in the certificate (e.g.,
      see: X.509 public key certificate), such as the identity of the
      certificate's subject and the ownership of a public key. (See:
      certification.)

      (C) To "certify a public key" means to issue a public-key
      certificate that vouches for the binding between the certificate's
      subject and the key.

      2. (I) The act by which a CA employs measures to verify the truth,
      accuracy, and binding between data items in a digital certificate.

      (C) A description of the measures used for verification should be
      included in the CA's CPS.

   $ CFB
      See: cipher feedback.

   $ Challenge Handshake Authentication Protocol (CHAP)
      (I) A peer entity authentication method for PPP, using a randomly-
      generated challenge and requiring a matching response that depends
      on a cryptographic hash of the challenge and a secret key. [R1994]
      (See: challenge-response, PAP.)

   $ challenge-response
      (I) An authentication process that verifies an identity by
      requiring correct authentication information to be provided in
      response to a challenge. In a computer system, the authentication
      information is usually a value that is required to be computed in
      response to an unpredictable challenge value.



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   $ Challenge-Response Authentication Mechanism (CRAM)
      (I) IMAP4 usage: A mechanism [R2195], intended for use with IMAP4
      AUTHENTICATE, by which an IMAP4 client uses a keyed hash [RFC2104]
      to authenticate itself to an IMAP4 server. (See: POP3 APOP.)

      (C) The server includes a unique timestamp in its ready response
      to the client. The client replies with the client's name and the
      hash result of applying MD5 to a string formed from concatenating
      the timestamp with a shared secret that is known only to the
      client and the server.

   $ channel
      (I) An information transfer path within a system. (See: covert
      channel.)

   $ checksum
      (I) A value that (a) is computed by a function that is dependent
      on the contents of a data set and (b) is stored or transmitted
      together with the data, for the purpose of detecting changes in
      the data. (See: cyclic redundancy check, data integrity service,
      error detection code, hash, keyed hash, protected checksum.)

      (C) To gain confidence that a data set has not been changed, an
      entity that later uses the data can compute a checksum and compare
      it with the checksum that was stored or transmitted with the data.

      (C) Computer systems and networks employ checksums (and other
      mechanisms) to detect accidental changes in data. However, active
      wiretapping that changes data could also change an accompanying
      checksum to match the changed data. Thus, some checksum functions
      by themselves are not good countermeasures for active attacks. To
      protect against active attacks, the checksum function needs to be
      well-chosen (see: cryptographic hash), and the checksum result
      needs to be protected (see: digital signature, keyed hash).

   $ chosen-ciphertext attack
      (I) A cryptanalysis approach in which the analyst tries to
      determine the key from knowledge of plaintext that corresponds to
      ciphertext selected (dictated) by the analyst.

   $ chosen-plaintext attack
      (I) A cryptanalysis approach in which the analyst tries to
      determine the key from knowledge of ciphertext that corresponds to
      plaintext selected (dictated) by the analyst.

   $ CIAC
      See: Computer Incident Advisory Capability.

   $ CIK
      See: cryptographic ignition key.




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   $ cipher
      (I) A cryptographic algorithm for encryption and decryption.

   $ cipher block chaining (CBC)
      (I) An block cipher mode that enhances electronic codebook mode by
      chaining together blocks of ciphertext it produces [FP081] (See:
      [R1829, R2451].)

      (C) This mode operates by combining (exclusive OR-ing) the
      algorithm's ciphertext output block with the next plaintext block
      to form the next input block for the algorithm.

   $ cipher feedback (CFB)
      (I) An block cipher mode that enhances electronic code book mode
      by chaining together the blocks of ciphertext it produces and
      operating on plaintext segments of variable length less than or
      equal to the block length [FP081].

      (C) This mode operates by using the previously generated
      ciphertext segment as the algorithm's input (i.e., by "feeding
      back" the ciphertext) to generate an output block, and then
      combining (exclusive OR-ing) that output block with the next
      plaintext segment (block length or less) to form the next
      ciphertext segment.

   $ ciphertext

      (I) Data that has been transformed by encryption so that its
      semantic information content (i.e., its meaning) is no longer
      intelligible or directly available. (See: cleartext, plaintext.)

      (O) "Data produced through the use of encipherment. The semantic
      content of the resulting data is not available." [I7498 Part 2]

   $ ciphertext-only attack
      (I) A cryptanalysis approach in which the analyst tries to
      determine the key solely from knowledge of intercepted ciphertext
      (although the analyst may also know other clues, such as the
      cryptographic algorithm, the language in which the plaintext was
      written, the subject matter of the plaintext, and some probable
      plaintext words.)

   $ CIPSO
      See: Common IP Security Option.

   $ CKL
      See: compromised key list.

   $ class 2, 3, 4, or 5
      (O) U.S. Department of Defense usage: Levels of assurance based on
      risk and value of information to be protected [DOD3]:



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       - Class 2: For handling low-value information (unclassified, not
         mission-critical, or low monetary value) or protection of
         system-high information in low- to medium-risk environment.

       - Class 3: For handling medium-value information in low- to
         medium-risk environment. Typically requires identification of a
         system entity as a legal person, rather than merely a member of
         an organization.

       - Class 4: For handling medium- to high-value information in any
         environment. Typically requires identification of an entity as
         a legal person, rather than merely a member of an organization,
         and a cryptographic hardware token for protection of keying
         material.

       - Class 5: For handling high-value information in a high-risk
         environment.

   $ classification
   $ classification level
      (I) (1.) A grouping of classified information to which a
      hierarchical, restrictive security label is applied to increase
      protection of the data. (2.) The level of protection that is
      required to be applied to that information. (See: security level.)

   $ classified
      (I) Refers to information (stored or conveyed, in any form) that
      is formally required by a security policy to receive data
      confidentiality service and to be marked with a security label
      (which in some cases might be implicit) to indicate its protected
      status. (See: unclassified.)

      (C) The term is mainly used in government, especially in the
      military, although the concept underlying the term also applies
      outside government. In the U.S. Department of Defense, for
      example, it means information that has been determined pursuant to
      Executive Order 12958 ("Classified National Security Information",
      13 December 1996) or any predecessor order to require protection
      against unauthorized disclosure and is marked to indicate its
      classified status when in documentary form.

   $ clean system
      (I) A computer system in which the operating system and
      application system software and files have just been freshly
      installed from trusted software distribution media.

      (C) A clean system is not necessarily in a secure state.

   $ clearance
   $ clearance level
      (I) The security level of information to which a security
      clearance authorizes a person to have access.


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   $ cleartext
      (I) Data in which the semantic information content (i.e., the
      meaning) is intelligible or is directly available. (Compare with:
      plaintext.)

      (O) "Intelligible data, the semantic content of which is
      available." [I7498 Part 2]

      (D) ISPDs SHOULD NOT use this term loosely as a synonym for
      "plaintext", the input to an encryption operation, because the
      plaintext input to encryption may itself be ciphertext that was
      output from another operation. (See: superencryption.)

   $ client
      (I) A system entity that requests and makes use of a service
      provided by another system entity, which is called a server.

      (C) Usually, the requesting entity is a computer process, and it
      makes the request on behalf of a human user. In some cases, the
      server may itself be a client of some other server.

   $ CLIPPER chip
      (N) The Mykotronx, Inc. MYK-82, an integrated microcircuit with a
      cryptographic processor that implements the SKIPJACK encryption
      algorithm and supports key escrow. (See: CAPSTONE, Escrowed
      Encryption Standard.)

      (C) The key escrow scheme involves a SKIPJACK key common to all
      chips, a serial number unique to the chip, and a second SKIPJACK
      key that is unique to the chip and unlocks all data encrypted by
      the chip. The second key is escrowed as split key components held
      by NIST and the U.S. Treasury Department.

   $ closed security environment
      (O) DoD usage: A system environment that meets both of the
      following conditions: (a) Application developers (including
      maintainers) have sufficient clearances and authorizations to
      provide an acceptable presumption that they have not introduced
      malicious logic. (b) Configuration control provides sufficient
      assurance that system applications and the equipment they run on
      are protected against the introduction of malicious logic prior to
      and during the operation of applications. [NCS04] (See: open
      security environment.)

   $ code
      (I) noun: A system of symbols used to represent information, which
      might originally have some other representation. (See: encode.)

      (D) ISPDs SHOULD NOT use this term as synonym for the following:
       - Nouns: (1) "cipher" or other forms of "cryptographic
      algorithm", (2) "ciphertext".


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       - Verbs: "encrypt".

      (D) ISPDs SHOULD NOT this word as an abbreviation for the
      following terms: authentication code, country code, cyclic
      redundancy code, source code, data authentication code, error
      detection code, hash code, manipulation detection code, message
      authentication code, message integrity code


   $ color change
      (I) In a system that is being operated in periods processing mode,
      the act of purging all information from one processing period and
      then changing over to the next processing period.

   $ Common Criteria
   $ Common Criteria for Information Technology Security
      (N) "The Common Criteria" is an ISO standard for evaluating
      information technology products and systems, such as operating
      systems, computer networks, distributed systems, and applications.
      It states requirements for security functions and for assurance
      measures.

      (C) Canada, France, Germany, the Netherlands, the United Kingdom,
      and the United States (NIST and NSA) began developing this
      standard in 1993, based on the European ITSEC, the Canadian
      Trusted Computer Product Evaluation Criteria (CTCPEC), and the
      U.S. "Federal Criteria for Information Technology Security" (FC)
      and its precursor, the TCSEC. The U.S. Government intends that
      this standard will supersede both the TCSEC and FIPS PUB 140-1.
      (See: NIAP.)

      (C) The standard addresses data confidentiality, data integrity,
      and availability and may apply to other aspects of security. It
      focuses on threats to information arising from human activities,
      malicious or otherwise, but may apply to non-human threats. It
      applies to security measures implemented in hardware, firmware, or
      software. It does not apply to (a) administrative security not
      related directly to technical security, (b) technical physical
      aspects of security such as electromagnetic emanation control, (c)
      evaluation methodology or administrative and legal framework under
      which the criteria may be applied, (d) procedures for use of
      evaluation results, or (e) assessment of inherent qualities of
      cryptographic algorithms.

      (C) Work was done in cooperation with ISO/IEC Joint Technical
      Committee 1 (Information Technology), Subcommittee 27 (Security
      Techniques), Working Group 3 (Security Criteria). Version 2.0 of
      the Criteria [CCIB] is equivalent to International Standard 15408.

   $ Common IP Security Option (CIPSO)
      See: (secondary definition in) Internet Protocol Security Option.



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   $ common name
      (I) A character string that (a) may be a part of the X.500 DN of a
      Directory object ("commonName" attribute), (b) is a (possibly
      ambiguous) name by which the object is commonly known in some
      limited scope (such as an organization), and (c) conforms to the
      naming conventions of the country or culture with which it is
      associated. [X520] (See: ("subject" and "issuer" in) X.509 public-
      key certificate.)

      (C) For example, "Dr. Albert Einstein", "The United Nations", or
      "12-th Floor Laser Printer".

   $ communication security (COMSEC)
      (I) Measures that implement and assure security services in a
      communication system, particularly those that provide data
      confidentiality and data integrity and that authenticate
      communicating entities.

      (C) Usually understood to include cryptographic algorithms and key
      management methods and processes, devices that implement them, and
      the life cycle management of those keys and devices.

   $ community string
      (I) A community name in the form of an octet string that serves as
      a cleartext password in SNMP version 1 [R1157].

   $ compartment
      (I) A grouping of sensitive information items that require special
      access controls beyond those normally provided for the basic
      classification level of the information. (See: category.)

      (C) The term is usually understood to include the special handling
      procedures to be used for the information.

   $ compromise
      See: data compromise, security compromise.

   $ compromised key list (CKL)
      (O) MISSI usage: A list that identifies keys for which
      unauthorized disclosure or alteration may have occurred. (See:
      data compromise.)

   $ COMPUSEC
      See: computer security.

   $ computer emergency response team (CERT)
      (I) An organization that studies computer and network INFOSEC in
      order to provide incident response services to victims of attacks,
      publish alerts concerning vulnerabilities and threats, and offer
      other information to help improve computer and network security.
      (See: CSIRT, security incident.)



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      (C) For example, the CERT Coordination Center at Carnegie-Mellon
      University (sometimes called "the" CERT) and the Computer Incident
      Advisory Capability.

   $ Computer Incident Advisory Capability (CIAC)
      (N) A computer emergency response team in the U.S. Department of
      Energy.

   $ computer network
      (I) A collection of host computers together with the subnetwork or
      internetwork through which they can exchange data.

      (C) This definition is intended to cover systems of all sizes and
      types, ranging from the complex Internet to a simple system
      composed of a personal computer dialing in as a remote terminal of
      another computer.

   $ computer security (COMPUSEC)
      (I) Measures that implement and assure security services in a
      computer system, particularly those that assure access control
      service.

      (C) Usually understood to include functions, features, and
      technical characteristics of computer hardware and software,
      especially operating systems.

   $ computer security incident response team (CSIRT)
      (I) An organization "that coordinates and supports the response to
      security incidents that involve sites within a defined
      constituency." [R2350] (See: CERT, FIRST, security incident.)

      (C) To be considered a CSIRT, an organization must do as follows:

       - Provide a (secure) channel for receiving reports about
         suspected security incidents.
       - Provide assistance to members of its constituency in handling
         the incidents.
       - Disseminate incident-related information to its constituency
         and other involved parties.

   $ computer security object
      (I) The definition or representation of a resource, tool, or
      mechanism used to maintain a condition of security in computerized
      environments. Includes many elements referred to in standards that
      are either selected or defined by separate user communities.
      [CSOR] (See: object identifier, Computer Security Objects
      Register.)

   $ Computer Security Objects Register (CSOR)
      (N) A service operated by NIST is establishing a catalog for
      computer security objects to provide stable object definitions
      identified by unique names. The use of this register will enable


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      the unambiguous specification of security parameters and
      algorithms to be used in secure data exchanges.

      (C) The CSOR follows registration guidelines established by the
      international standards community and ANSI. Those guidelines
      establish minimum responsibilities for registration authorities
      and assign the top branches of an international registration
      hierarchy. Under that international registration hierarchy the
      CSOR is responsible for the allocation of unique identifiers under
      the branch: {joint-iso-ccitt(2) country(16) us(840) gov(101)
      csor(3)}.

   $ COMSEC
      See: communication security.

   $ confidentiality
      See: data confidentiality.

   $ configuration control
      (I) The process of regulating changes to hardware, firmware,
      software, and documentation throughout the development and
      operational life of a system. (See: administrative security.)

      (C) Configuration control helps protect against unauthorized or
      malicious alteration of a system and thus provides assurance of
      system integrity. (See: malicious logic.)

   $ confinement property
      See: (secondary definition in) Bell-LaPadula Model.

   $ connectionless data integrity service
      (I) A security service that provides data integrity service for an
      individual IP datagram, by detecting modification of the datagram,
      without regard to the ordering of the datagram in a stream of
      datagrams.

      (C) A connection-oriented data integrity service would be able to
      detect lost or reordered datagrams within a stream of datagrams.

   $ contingency plan
      (I) A plan for emergency response, backup operations, and post-
      disaster recovery in a system as part of a security program to
      ensure availability of critical system resources and facilitate
      continuity of operations in a crisis. [NCS04] (See: availability.)

   $ controlled security mode
      (D) ISPDs SHOULD NOT use this term. It was defined in an earlier
      version of the U.S. Department of Defense policy that regulates
      system accreditation, but was subsumed by "partitioned security
      mode" in the current version. [DOD2]

      (C) The term refers to a mode of operation of an information


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      system, wherein at least some users with access to the system have
      neither a security clearance nor a need-to-know for all classified
      material contained in the system; however, separation and control
      of users and classified material on the basis, respectively, of
      clearance and classification level are not essentially under
      operating system control as they are in "multilevel security
      mode".

      (C) This mode was intended to encourage ingenuity in meeting the
      security requirements of Defense policy in ways less restrictive
      than dedicated security mode and system high security mode, but at
      a level of risk lower than that generally associated with the true
      multilevel security mode. This was to be accomplished by
      implementation of explicit augmenting measures to reduce or remove
      a substantial measure of system software vulnerability together
      with specific limitation of the security clearance levels of users
      permitted concurrent access to the system.

   $ cookie
      (I) access control usage: A synonym for "capability" or "ticket"
      in an access control system.

      (I) IPsec usage: Data exchanged by ISAKMP to prevent certain
      denial of service attacks at the establishment of a security
      association.

      (I) HTTP usage: Data exchanged between an HTTP server and a
      browser (a client of the server) to store state information on the
      client side and retrieve it later for server use.

      (C) An HTTP server, when sending data to a client, may send along
      a cookie, which the client retains after the HTTP connection
      closes. A server can use this mechanism to maintain persistent
      client-side state information for HTTP-based applications,
      retrieving the state information in later connections. A cookie
      includes a description of the range of URLs for which the state is
      valid. Future requests made by the client in that range will also
      send the current value of the cookie to the server. Cookies can be
      used to generate profiles of web usage habits, and thus may
      infringe on personal privacy.

   $ Coordinated Universal Time (UTC)
      (N) UTC is derived from International Atomic Time (TAI) by adding
      a number of leap seconds. The International Bureau of Weights and
      Measures computes TAI once each month by averaging data from many
      laboratories. (See: GeneralizedTime, UTCTime.)

   $ copy
      See: card copy.

   $ correctness integrity
      (I) Accuracy and consistency of the information that data values


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      represent, rather than of the data itself. Closely related to
      issues of accountability and error handling. (See: data integrity,
      source integrity.)

   $ correctness proof
      (I) A mathematical proof of consistency between a specification
      for system security and the implementation of that specification.
      (See: formal specification.)

   $ countermeasure
      (I) An action, device, procedure, or technique that reduces a
      threat, a vulnerability, or an attack by eliminating or preventing
      it, by minimizing the harm it can cause, or by discovering and
      reporting it so that corrective action can be taken.

      (C) In an Internet protocol, a countermeasure may take the form of
      a protocol feature, an element function, or a usage constraint.

   $ country code
      (I) An identifier that is defined for a nation by ISO. [I3166]

      (C) For each nation, ISO Standard 3166 defines a unique two-
      character alphabetic code, a unique three-character alphabetic
      code, and a 3-digit code. Among many uses of these codes, the two-
      character codes are used as top-level domain names.

   $ covert channel
      (I) A intra-system channel that permits two cooperating entities,
      without exceeding their access authorizations, to transfer
      information in a way that violates the system's security policy.
      (See: channel, out of band.)

      (O) "A communications channel that allows two cooperating
      processes to transfer information in a manner that violates the
      system's security policy." [NCS04]

      (C) The cooperating entities can be either two insiders or an
      insider and an outsider. Of course, an outsider has no access
      authorization at all. A covert channel is a system feature that
      the system architects neither designed nor intended for
      information transfer:

       - "Timing channel": A system feature that enable one system
         entity to signal information to another by modulating its own
         use of a system resource in such a way as to affect system
         response time observed by the second entity.

       - "Storage channel": A system feature that enables one system
         entity to signal information to another entity by directly or
         indirectly writing a storage location that is later directly or
         indirectly read by the second entity.



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   $ CPS
      See: certification practice statement.

   $ cracker
      (I) Someone who tries to break the security of, and gain access
      to, someone else's system without being invited to do so. (See:
      hacker and intruder.)

   $ CRAM
      See: Challenge-Response Authentication Mechanism.

   $ CRC
      See: cyclic redundancy check.

   $ credential(s)
      (I) Data that is transferred or presented to establish either a
      claimed identity or the authorizations of a system entity. (See:
      authentication information.)

      (O) "Data that is transferred to establish the claimed identity of
      an entity." [I7498 Part 2]

   $ critical
      1. (I) "Critical" system resource: A condition of a service or
      other system resource such that denial of access to that resource
      would jeopardize a system user's ability to perform a primary
      function or would result in other serious consequences. (See:
      availability, sensitive.)

      2. (N) "Critical" extension: Each extension of an X.509
      certificate (or CRL) is marked as being either critical or non-
      critical. If an extension is critical and a certificate user (or
      CRL user) does not recognize the extension type or does not
      implement its semantics, then the user is required to treat the
      certificate (or CRL) as invalid. If an extension is non-critical,
      a user that does not recognize or implement that extension type is
      permitted to ignore the extension and process the rest of the
      certificate (or CRL).

   $ CRL
      See: certificate revocation list.

   $ CRL distribution point
      See: distribution point.

   $ CRL extension
      See: extension.

   $ cross-certificate
      See: cross-certification.




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   $ cross-certification
      (I) The act or process by which two CAs each certify a public key
      of the other, issuing a public-key certificate to that other CA.

      (C) Cross-certificates enable two certificate users to validate
      each other's certificate, even when the users are certified under
      different certification hierarchies.

   $ cryptanalysis
      (I) The mathematical science that deals with analysis of a
      cryptographic system in order to gain knowledge needed to break or
      circumvent the protection that the system is designed to provide.
      (See: cryptology.)

      (O) "The analysis of a cryptographic system and/or its inputs and
      outputs to derive confidential variables and/or sensitive data
      including cleartext." [I7498 Part 2]

      (C) The "O" definition states the traditional goal of
      cryptanalysis--convert the ciphertext to plaintext (which usually
      is cleartext) without knowing the key--but that definition applies
      only to encryption systems. Today, the term is used with reference
      to all kinds of cryptographic algorithms and key management, and
      the "I" definition reflects that. In all cases, however, a
      cryptanalyst tries to uncover or reproduce someone else's
      sensitive data, such as cleartext, a key, or an algorithm. The
      basic cryptanalytic attacks on encryption systems are ciphertext-
      only, known-plaintext, chosen-plaintext, and chosen-ciphertext;
      and these generalize to the other kinds of cryptography.

   $ crypto
      (D) Except as part of certain long-established terms listed in
      this Glossary, ISPDs SHOULD NOT use this abbreviated term because
      it may be misunderstood. Instead, use "cryptography" or
      "cryptographic".

   $ cryptographic algorithm
      (I) An algorithm that employs the science of cryptography,
      including encryption algorithms, cryptographic hash algorithms,
      digital signature algorithms, and key agreement algorithms.

   $ cryptographic application programming interface (CAPI)
      (I) The source code formats and procedures through which an
      application program accesses cryptographic services, which are
      defined abstractly compared to their actual implementation. For
      example, see: PKCS #11, [R2628].

   $ cryptographic card
      (I) A cryptographic token in the form of a smart card or a PC
      card.




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   $ cryptographic component
      (I) A generic term for any system component that involves
      cryptography. (Compare with: cryptographic module.)

   $ cryptographic hash
      See: (secondary definition in) hash function.

   $ cryptographic ignition key (CIK)
      (I) A physical (usually electronic) token used to store,
      transport, and protect cryptographic keys. (Sometimes abbreviated
      as "crypto ignition key".)

      (C) A typical use is to divide a split key between a CIK and a
      cryptographic module, so that it is necessary to combine the two
      to regenerate a key-encrypting key and thus activate the module
      and other keys it contains.

   $ cryptographic key
      (I) Usually shortened to just "key". An input parameter that
      varies the transformation performed by a cryptographic algorithm.

      (O) "A sequence of symbols that controls the operations of
      encipherment and decipherment." [I7498 Part 2]

      (C) If a key value needs to be kept secret, the sequence of
      symbols (usually bits) that comprise it should be random, or at
      least pseudo-random, because that makes the key hard for an
      adversary to guess. (See: cryptanalysis, brute force attack.)

   $ Cryptographic Message Syntax (DMS)
      (I) A encapsulation syntax (R2630] for digital signatures, hashes,
      and encryption of arbitrary messages.

      (C) The syntax was derived from PKCS #7. CMS values are specified
      with ASN.1 and use BER encoding. The syntax permits multiple
      encapsulation with nesting, permits arbitrary attributes to be
      signed along with message content, and supports a variety of
      architectures for digital certificate-based key management.

   $ cryptographic module
      (I) A set of hardware, software, firmware, or some combination
      thereof that implements cryptographic logic or processes,
      including cryptographic algorithms, and is contained within the
      module's cryptographic boundary, which is an explicitly defined
      contiguous perimeter that establishes the physical bounds of the
      module. [FP140]

   $ cryptographic system
      (I) A set of cryptographic algorithms together with the key
      management processes that support the use of the algorithms in
      some application context.



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      (C) This definition covers a wider range of algorithms than the
      following definition from X.509:

      (O) "A collection of transformations from plaintext into
      ciphertext and vice versa [which would exclude digital signature,
      cryptographic hash, and key agreement algorithms], the particular
      transformation(s) to be used being selected by keys. The
      transformations are normally defined by a mathematical algorithm."
      [X509]

   $ cryptographic token
      (I) A portable, user-controlled, physical device used to store
      cryptographic information and possibly perform cryptographic
      functions. (See: cryptographic card, token.)

      (C) A smart token may implement some set of cryptographic
      algorithms and may implement related algorithms and key management
      functions, such as a random number generator. A smart
      cryptographic token may contain a cryptographic module or may not
      be explicitly designed that way.

   $ cryptography
      (I) The mathematical science that deals with transforming data to
      render its meaning unintelligible (i.e., to hide its semantic
      content), prevent its undetected alteration, or prevent its
      unauthorized use. If the transformation is reversible,
      cryptography also deals with restoring encrypted data to
      intelligible form. (See: cryptology. Compare with: steganography.)

      (O) "The discipline which embodies principles, means, and methods
      for the transformation of data in order to hide its information
      content, prevent its undetected modification and/or prevent its
      unauthorized use. . . . Cryptography determines the methods used
      in encipherment and decipherment." [I7498 Part 2]

   $ Cryptoki
      See: (secondary definition in) PKCS #11.

   $ cryptology
      (I) The science that includes both cryptography and cryptanalysis,
      and sometimes is said to include steganography.

   $ cryptonet
      (I) A group of system entities that share a secret cryptographic
      key for a symmetric algorithm.

   $ cryptoperiod
      (I) The time span during which a particular key is authorized to
      be used in a cryptographic system. (See: key management.)

      (C) A cryptoperiod is usually stated in terms of calendar or clock
      time, but sometimes is stated in terms of the maximum amount of


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      data permitted to be processed by a cryptographic algorithm using
      the key. Specifying a cryptoperiod involves a tradeoff between the
      cost of rekeying and the risk of successful cryptoanalysis.

      (C) Although we deprecate its prefix, this term is long-
      established in COMPUSEC usage. (See: crypto) In the context of
      certificates and public keys, "key lifetime" and "validity period"
      are often used instead.

   $ cryptosystem
      (D) ISPDs SHOULD NOT use this term as an abbreviation for
      cryptographic system. (For rationale, see: crypto.)

   $ CSIRT
      See: computer security incident response team.

   $ CSOR
      See: Computer Security Objects Register.

   $ cut-and-paste attack
      (I) An active attack on the data integrity of ciphertext, effected
      by replacing sections of ciphertext with other ciphertext, such
      that the result appears to decrypt correctly but actually decrypts
      to plaintext that is forged to the satisfaction of the attacker.

   $ cyclic redundancy check (CRC)
      (I) Sometimes called "cyclic redundancy code". A type of checksum
      algorithm that is not a cryptographic hash but is used to
      implement data integrity service where accidental changes to data
      are expected.

   $ DAC
      See: Data Authentication Code, discretionary access control.

   $ DASS
      See: Distributed Authentication Security Service.

   $ data
      (I) Information in a specific physical representation, usually a
      sequence of symbols that have meaning; especially a representation
      of information that can be processed or produced by a computer.

   $ Data Authentication Algorithm
      (N) A keyed hash function equivalent to DES cipher block chaining
      with IV = 0 [A9009].

      (D) ISPDs SHOULD NOT use this term in an uncapitalized (i.e.,
      lower case) form as a general synonym for other kinds of
      checksums.

   $ data authentication code vs. Data Authentication Code (DAC)
      1. (N) Capitalized: "The Data Authentication Code" refers to a


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      U.S. Government standard [FP113] for a checksum that is computed
      by the Data Authentication Algorithm. (Also known as the ANSI
      standard Message Authentication Code [A9009].)

      2. (D) Not capitalized: ISPDs SHOULD NOT use "data authentication
      code" as a general synonym for other kinds of checksums, because
      this term mixes concepts in a potentially misleading way. Instead,
      use "checksum", "error detection code", "hash", "keyed hash",
      "Message Authentication Code", or "protected checksum", depending
      on what is meant.

   $ data compromise
      (I) A security incident in which information is exposed to
      potential unauthorized access, such that unauthorized disclosure,
      alteration, or use of the information may have occurred. (See:
      compromise.)

   $ data confidentiality
      (I) "The property that information is not made available or
      disclosed to unauthorized individuals, entities, or processes
      [i.e., to any unauthorized system entity]." [I7498 Part 2]. (See:
      data confidentiality service.)

      (D) ISPDs SHOULD NOT use this term as a synonym for "privacy",
      which is a different concept.

   $ data confidentiality service
      (I) A security service that protects data against unauthorized
      disclosure. (See: data confidentiality.)

      (D) ISPDs SHOULD NOT use this term as a synonym for "privacy",
      which is a different concept.

   $ Data Encryption Algorithm (DEA)
      (N) A symmetric (see: symmetric cryptography) block cipher that
      uses a 64-bit key, of which 56 bits are independently chosen and 8
      are parity bits. It maps a 64-bit block into another 64-bit block.
      [FP046]

      (C) This algorithm is usually referred to as "DES". (See: Data
      Encryption Standard.) The algorithm has also been adopted in
      standards outside the Government (e.g., [A3092]).

   $ data encryption key (DEK)
      (I) A cryptographic key that is used to encipher application data.
      (See: key-encrypting key.)

   $ Data Encryption Standard (DES)
      (N) A U.S. Government standard [FP046] that specifies the Data
      Encryption Algorithm and states policy for using the algorithm to
      protect unclassified, sensitive data. (See: AES.)



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   $ data integrity
      (I) The property that data has not been changed, destroyed, or
      lost in an unauthorized or accidental manner.

      (O) "The property that information has not been modified or
      destroyed in an unauthorized manner." [I7498 Part 2]

      (C) Deals with constancy of and confidence in data values, not
      with the information that the values represent (see: correctness
      integrity) or the trustworthiness of the source of the values
      (see: source integrity).

   $ data integrity service
      (I) A security service that protects against unauthorized changes
      to data, including both intentional change or destruction and
      accidental change or loss, by ensuring that changes to data are
      detectable. (See: data integrity.)

      (C) A data integrity service can only detect a change and report
      it to an appropriate system entity; changes cannot be prevented
      unless the system is perfect (error-free) and no malicious user
      has access. However, a system that offers data integrity service
      might also attempt to correct and recover from changes.

      (C) Relationship between data integrity service and authentication
      services. Although data integrity service is defined separately
      from data origin authentication service and peer entity
      authentication service, it is closely related to them.
      Authentication services depend, by definition, on companion data
      integrity services. Data origin authentication service provides
      verification that the identity of the original source of a
      received data unit is as claimed; there can be no such
      verification if the data unit has been altered. Peer entity
      authentication service provides verification that the identity of
      a peer entity in a current association is as claimed; there can be
      no such verification if the claimed identity has been altered.

   $ data origin authentication
      (I) "The corroboration that the source of data received is as
      claimed." [I7498 Part 2] (See: authentication.)

   $ data origin authentication service
      (I) A security service that verifies the identity of a system
      entity that is claimed to be the original source of received data.
      (See: authentication, authentication service.)

      (C) This service is provided to any system entity that receives or
      holds the data. Unlike peer entity authentication service, this
      service is independent of any association between the originator
      and the recipient, and the data in question may have originated at
      any time in the past.



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      (C) A digital signature mechanism can be used to provide this
      service, because an adversary, who does not know the private key
      of the signer, cannot forge the correct signature. However, by
      using the signer's public key, anyone can verify the origin of
      correctly signed data.

      (C) This service is usually bundled with connectionless data
      integrity service. (See: "relationship between data integrity
      service and authentication services" under data integrity service.

   $ data privacy
      (D) ISPDs SHOULD NOT use this term because it mix concepts in a
      potentially misleading way. Instead, use "data confidentiality" or
      "privacy", depending on what is meant.

   $ data security
      (I) The protection of data from disclosure, alteration,
      destruction, or loss that either is accidental or is intentional
      but unauthorized.

      (C) Both data confidentiality service and data integrity service
      are needed to achieve data security.

   $ datagram
      (I) "A self-contained, independent entity of data carrying
      sufficient information to be routed from the source to the
      destination." [R1983]

   $ DEA
      See: Data Encryption Algorithm.

   $ deception
      See: (secondary definition in) threat consequence.

   $ decipher
      (D) ISPDs SHOULD NOT use this term as a synonym for "decrypt".
      However, see the usage note under "encryption".

   $ decipherment
      (D) ISPDs SHOULD NOT use this term as a synonym for "decryption",
      except in special circumstances. (See: (usage discussion under)
      encryption.)

   $ decode
      (I) Convert encoded data back to its original form of
      representation. (Compare with: decrypt.)

      (D) ISPDs SHOULD NOT use this term as a synonym for "decrypt",
      because that would mix concepts in a potentially misleading way.

   $ decrypt
      (I) Cryptographically restore ciphertext to the plaintext form it


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      had before encryption.

   $ decryption
      See: (secondary definition in) encryption.

   $ dedicated security mode
      (I) A mode of operation of an information system, wherein all
      users have the clearance or authorization, and the need-to-know,
      for all data handled by the system. In this mode, the system may
      handle either a single classification level or category of
      information or a range of levels and categories.

      (C) This mode is defined formally in U.S. Department of Defense
      policy regarding system accreditation [DOD2], but the term is also
      used outside the Defense Department and outside the Government.

   $ default account
      (I) A system login account (user name and password) that has been
      predefined in a manufactured system to permit initial access when
      the system is first put into service.

      (C) Sometimes, the default user name and password are the same in
      each copy of the system. In any case, when the system is put into
      service, the default password should immediately be changed or the
      default account should be disabled.

   $ degauss
      (N) Apply a magnetic field to permanently remove, erase, or clear
      data from a magnetic storage medium, such as a tape or disk
      [NCS25]. Reduce magnetic flux density to zero by applying a
      reversing magnetic field.

   $ degausser
      (N) An electrical device that can degauss magnetic storage media.

   $ DEK
      See: data encryption key.

   $ delta CRL
      (I) A partial CRL that only contains entries for X.509
      certificates that have been revoked since the issuance of a prior,
      base CRL. This method can be used to partition CRLs that become
      too large and unwieldy.

   $ denial of service
      (I) The prevention of authorized access to a system resource or
      the delaying of system operations and functions. (See:
      availability, critical (resource of a system), flooding.)

   $ DES
      See: Data Encryption Standard.



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   $ dictionary attack
      (I) An attack that uses a brute-force approach of successively
      trying all the words in some large, exhaustive list.

      (C) For example, an attack on an authentication service by trying
      all possible passwords; or an attack on encryption by encrypting
      some known plaintext phrase with all possible keys so that the key
      for any given encrypted message containing that phrase may be
      obtained by lookup.

   $ Diffie-Hellman
      (N) A key agreement algorithm published in 1976 by Whitfield
      Diffie and Martin Hellman [DH76, R2631].

      (C) Diffie-Hellman does key establishment, not encryption.
      However, the key that it produces may be used for encryption, for
      further key management operations, or for any other cryptography.

      (C) The difficulty of breaking Diffie-Hellman is considered to be
      equal to the difficulty of computing discrete logarithms modulo a
      large prime. The algorithm is described in [R2631] and [Schn]. In
      brief, Alice and Bob together pick large integers that satisfy
      certain mathematical conditions, and then use the integers to each
      separately compute a public-private key pair. They send each other
      their public key. Each person uses their own private key and the
      other person's public key to compute a key, k, that, because of
      the mathematics of the algorithm, is the same for each of them.
      Passive wiretapping cannot learn the shared k, because k is not
      transmitted, and neither are the private keys needed to compute k.
      However, without additional mechanisms to authenticate each party
      to the other, a protocol based on the algorithm may be vulnerable
      to a man-in-the-middle attack.

   $ digest
      See: message digest.

   $ digital certificate
      (I) A certificate document in the form of a digital data set (a
      data object used by a computer) to which is appended a computed
      digital signature value that depends on the data set. (See:
      attribute certificate, public-key certificate.)

      (D) ISPDs SHOULD NOT use this term to refer to a signed CRL or
      CKL. Although the recommended definition can be interpreted to
      include those items, the security community does not use the term
      with those meanings.

   $ digital certification
      (D) ISPDs use this term as a synonym for "certification", unless
      the context is not sufficient to distinguish between digital
      certification and another kind of certification, in which case it
      would be better to use "public-key certification" or another


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      phrase that indicates what is being certified.

   $ digital document
      (I) An electronic data set that represents the information
      originally written in a document in a different medium (usually
      paper) or is an analogue of documents of that type.

   $ digital envelope
      (I) A digital envelope for a recipient is a combination of (a)
      encrypted content data (of any kind) and (b) the content
      encryption key in an encrypted form that has been prepared for the
      use of the recipient.

      (C) In ISPDs, this term should be defined at the point of first
      use because, although the term is defined in PKCS #7 and used in
      S/MIME, it is not yet widely-established.

      (C) Digital enveloping is not simply a synonym for implementing
      data confidentiality with encryption; digital enveloping is a
      hybrid encryption scheme to "seal" a message or other data, by
      encrypting the data and sending both it and a protected form of
      the key to the intended recipient, so that no one other than the
      intended recipient can "open" the message. In PCKS #7, it means
      first encrypting the data using a symmetric encryption algorithm
      and a secret key, and then encrypting the secret key using an
      asymmetric encryption algorithm and the public key of the intended
      recipient. In S/MIME, additional methods are defined for
      encrypting the content encryption key.

   $ Digital ID(service mark)
      (D) ISPDs SHOULD NOT use this term as a synonym for "digital
      certificate" because (a) it is the service mark of commercial
      firm, (b) it unnecessarily duplicates the meaning of other, well-
      established terms, and (c) a certificate is not always used as
      authentication information. In some contexts, however, it may be
      useful to explain that the key conveyed in a public-key
      certificate can be used to verify an identity and thus the
      certificate can be thought of as digital identification
      information. (See: identification information.)

   $ digital key
      (C) The adjective "digital" need not be used with "key" or
      "cryptographic key", unless the context is insufficient to
      distinguish the key from another kind of key, such as a metal key
      for a door lock.

   $ digital notary
      (I) Analogous to a notary public; provides a trusted date-and-time
      stamp for a document that proves the document existed at a point
      in time, and may also verify the signatures on a signed document.
      (See: notarization.)



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   $ digital signature
      (I) A value computed with a cryptographic algorithm and appended
      to a data set in such a way that any recipient of the data can use
      the signature to verify the data's origin and integrity. (See:
      data origin authentication service, data integrity service,
      digitized signature, electronic signature, signer.)

      (I) "Data appended to, or a cryptographic transformation of, a
      data unit that allows a recipient of the data unit to prove the
      source and integrity of the data unit and protect against forgery,
      e.g. by the recipient." [I7498 Part 2]

      (C) Typically, the data set is first input to a hash function, and
      then the hash result is cryptographically transformed using a
      private key of the signer. The final resulting value is called the
      digital signature of the data set. The signature value is a
      protected checksum, because the properties of a cryptographic hash
      ensure that if the data set is changed, the digital signature will
      no longer match it. The digital signature is unforgeable because
      one cannot be certain of correctly creating or changing the
      signature without knowing the private key of the supposed signer.

      (C) Some digital signature schemes use an asymmetric encryption
      algorithms (e.g., see: RSA) to transform the hash result. Thus,
      when Alice needs to sign a message to send to Bob, she can encrypt
      the hash result using her private key. Bob receives both the
      message and the digital signature. Bob decrypts the signature
      using Alice's public key and compares the plaintext result to the
      hash result that he computes by hashing the message himself. If
      the values are equal, Bob accepts the message because he is
      certain that it is from Alice and has arrived unchanged. If the
      values are not equal, Bob rejects the message because either the
      message or the signature was altered in transit.

      (C) Other digital signature schemes (e.g., see: DSS) transform the
      hash result with an algorithm (e.g., see: DSA, El Gamal) that
      cannot be directly used to encrypt data. Such a scheme creates a
      signature value from the hash, and provides a way to verify the
      signature value, but does not provide a way to recover the hash
      result from the signature value. In some countries, such a scheme
      may improve exportability and avoid other legal constraints on
      usage. Alice sends the signature value to Bob along with both the
      message and its hash result. The algorithm enables Bob to use
      Alice's public signature key and the signature value to verify the
      hash result he receives. Then, as before, he compares that hash
      result she sent to the one that he computes by hashing the message
      himself.

   $ Digital Signature Algorithm (DSA)
      (N) An asymmetric cryptographic algorithm that produces a digital
      signature in the form of a pair of large numbers. The signature is
      computed using rules and parameters such that the identity of the


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      signer and the integrity of the signed data can be verified. (See:
      Digital Signature Standard.)

   $ Digital Signature Standard (DSS)
      (N) The U.S. Government standard [FP186] that specifies the
      Digital Signature Algorithm (DSA), which involves asymmetric
      cryptography.

   $ digital watermarking
      (I) Computing techniques for inseparably embedding unobtrusive
      marks or labels as bits in digital data--text, graphics, images,
      video, or audio--and for detecting or extracting the marks later.

      (C) The set of embedded bits (the digital watermark) is sometimes
      hidden, usually imperceptible, and always intended to be
      unobtrusive. Depending on the particular technique that is used,
      digital watermarking can assist in proving ownership, controlling
      duplication, tracing distribution, ensuring data integrity, and
      performing other functions to protect intellectual property
      rights. [ACM]

   $ digitized signature
      (D) ISPDs SHOULD NOT use this term because there is no current
      consensus on its definition. Although it appears to be used mainly
      to refer to various forms of digitized images of handwritten
      signatures, the term should be avoided because it might be
      confused with "digital signature".

   $ directory
   $ Directory
      See: directory vs. Directory.

   $ Directory Access Protocol (DAP)
      (N) An OSI protocol [X519] for communication between a Directory
      User Agent (a client) and a Directory System Agent (a server).
      (See: Lightweight Directory Access Protocol.)

   $ directory vs. Directory
      1. (I) Not capitalized: The term "directory" refers generically to
      a database server or other system that provides information--such
      as a digital certificate or CRL--about an entity whose name is
      known.

      2. (I) Capitalized: "Directory" refers specifically to the X.500
      Directory. (See: repository.)

   $ disaster plan
      (D) A synonym for "contingency plan". In the interest of
      consistency, ISPDs SHOULD use "contingency plan" instead of
      "disaster plan".




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   $ disclosure (i.e., unauthorized disclosure)
      See: (secondary definition in) threat consequence.

   $ discretionary access control (DAC)
      (I) An access control service that enforces a security policy
      based on the identity of system entities and their authorizations
      to access system resources. (See: access control list, identity-
      based security policy, mandatory access control.)

      (C) This service is termed "discretionary" because an entity might
      have access rights that permit the entity, by its own volition, to
      enable another entity to access some resource.

      (O) "A means of restricting access to objects based on the
      identity of subjects and/or groups to which they belong. The
      controls are discretionary in the sense that a subject with a
      certain access permission is capable of passing that permission
      (perhaps indirectly) on to any other subject." [DOD1]

   $ disruption
      See: (secondary definition in) threat consequence.

   $ Distinguished Encoding Rules (DER)
      (N) A subset of the Basic Encoding Rules, which gives exactly one
      way to represent any ASN.1 value as an octet string [X690].

      (C) Since there is more than one way to encode ASN.1 in BER, DER
      is used in applications in which a unique encoding is needed, such
      as when a digital signature is computed on an ASN.1 value.

   $ distinguished name (DN)
      (I) An identifier that uniquely represents an object in the X.500
      Directory Information Tree (DIT) [X501]. (See: domain name.)

      (C) A DN is a set of attribute values that identify the path
      leading from the base of the DIT to the object that is named. An
      X.509 public-key certificate or CRL contains a DN that identifies
      its issuer, and an X.509 attribute certificate contains a DN or
      other form of name that identifies its subject.

   $ Distributed Authentication Security Service (DASS)
      (I) An experimental Internet protocol [R1507] that uses
      cryptographic mechanisms to provide strong, mutual authentication
      services in a distributed environment.

   $ distribution point
      (I) An X.500 Directory entry or other information source that is
      named in a v3 X.509 public-key certificate extension as a location
      from which to obtain a CRL that may list the certificate.

      (C) A v3 X.509 public-key certificate may have a
      "cRLDistributionPoints" extension that names places to get CRLs on


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      which the certificate might be listed. A CRL obtained from a
      distribution point may cover either all reasons for which a
      certificate might be revoked or only some of that reasons, may be
      issued by either the authority that signed the certificate or some
      other authority, and may contain revocation entries for only a
      subset of the full set of certificates issued by one CA or may
      contain revocation entries for multiple CAs.

   $ DN
      See: distinguished name.

   $ DNS
      See: Domain Name System.

   $ DOI
      See: Domain of Interpretation.

   $ domain
      (I) General security usage: An environment or context that defines
      the set of system resources that a set entities (perhaps defined
      by a security policy, or security model, or security architecture)
      has the right to access. (See: domain of interpretation, security
      perimeter.)

      (I) Internet usage: That part of the Internet domain name space
      tree [R1034] that is at or below the name the specifies the
      domain. A domain is a subdomain of another domain if it is
      contained within that domain. For example, D.C.B.A is a subdomain
      of C.B.A. (See: Domain Name System.)

      (O) MISSI usage: The domain of a MISSI certification authority is
      the set of MISSI users whose certificates are signed by the
      authority.

      (O) OSI usage: An administrative partition of a complex
      distributed OSI system.

   $ domain name
      (I) The style of identifier--a sequence of case-insensitive ASCII
      labels separated by dots ("bbn.com.")--defined for subtrees in the
      Internet Domain Name System [R1034] and used in other Internet
      identifiers, such as host names ("rosslyn.bbn.com."), mailbox
      names ("rshirey@bbn.com."), and URLs
      ("http://www.rosslyn.bbn.com/foo"). (See: domain and distinguished
      name.)

      (C) The domain name space of the DNS is a tree structure in which
      each node and leaf holds records describing a resource. Each node
      has a label. The domain name of a node is the list of labels on
      the path from the node to the root of the tree. The labels in a
      domain name are printed or read left to right, from the most
      specific (lowest, farthest from the root) to the least specific


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      (highest, closest to the root). The root's label is the null
      string, so a complete domain name ends in a dot. The top-level
      domains, those immediately below the root, include COM, EDU, GOV,
      INT, MIL, NET, ORG, and two-letter country codes (such as US) from
      ISO-3166. [R1591] (Also see: country code.)

   $ Domain Name System (DNS)
      (I) The main Internet operations database, which is distributed
      over a collection of servers and used by client software for
      purposes such as translating a domain name-style host name into an
      IP address (for example, "rosslyn.bbn.com" is "192.1.7.10") and
      locating a host that accepts mail for some mailbox address.
      [R1034]

      (C) The DNS has three major components:

       - Domain name space and resource records: Specifications for the
         tree-structured domain name space, and data associated with the
         names.

       - Name servers: Programs that hold information about a subset of
         the tree's structure and data holdings, and also hold pointers
         to other name servers that can provide information from any
         part of the tree.

       - Resolvers: Programs that extract information from name servers
         in response to client requests; typically, system routines
         directly accessible to user programs.

      (C) Extensions to the DNS [R2065, R2137] support key distribution
      for public keys needed for the DNS and for other protocols, data
      origin authentication service and data integrity service for
      resource records, data origin authentication service for
      transactions between resolvers and servers, and access control of
      records.

   $ domain of interpretation (DOI)
      (I) IPsec usage: An IPsec ISAKMP/IKE domain of interpretation
      (DOI) defines payload formats, exchange types, and conventions for
      naming security-relevant information such as security policies or
      cryptographic algorithms and modes.

      (C) For example, see [R2407]. The DOI concept is based on work by
      the TSIG CIPSO Working Group.

   $ dominate
      (I) Security level A is said to "dominate" security level B if the
      hierarchical classification level of A is greater (higher) than or
      equal to that of B and the nonhierarchical categories of A include
      all of those of B.




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   $ dongle
      (I) A portable, physical, electronic device that is required to be
      attached to a computer to enable a particular software program to
      run. (See: token.)

      (C) A dongle is essentially a physical key used for copy
      protection of software, because the program will not run unless a
      matching dongle is attached. When the software runs, it
      periodically queries the dongle and quits if the dongle does not
      reply with the proper authentication information. Dongles were
      originally constructed as an EPROM to be connected to a serial I/O
      port of a personal computer.

   $ downgrade
      (I) Reduce the classification level of information in an
      authorized manner.

   $ draft RFC
      (D) ISPDs SHOULD NOT use this term, because the Request for
      Comment series is archival in nature and does not have a "draft"
      category. Instead, use "Internet Draft".

   $ DSA
      See: Digital Signature Algorithm.

   $ DSS
      See: Digital Signature Standard.

   $ dual control
      (I) A procedure that uses two or more entities (usually persons),
      operating in concert, to protect a system resource such that no
      single entity acting alone can access that resource. (See: no-lone
      zone, separation of duties, split knowledge.)

   $ dual signature
      (D) ISPDs SHOULD NOT use this term except when stated as
      "SET(trademark) dual signature" with the following meaning:

      (O) SET usage: A single digital signature that protects two
      separate messages by including the hash results for both sets in a
      single encrypted value. [SET2]

      (C) Generated by hashing each message separately, concatenating
      the two hash results, and then hashing that value and encrypting
      the result with the signer's private key. Done to reduce the
      number of encryption operations and to allow verification of data
      integrity without complete disclosure of the data.

   $ EAP
      See: Extensible Authentication Protocol




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   $ eavesdropping
      (I) Passive wiretapping done secretly, i.e., without the knowledge
      of the originator or the intended recipients of the communication.

   $ ECB
      See: electronic codebook.

   $ ECDSA
      See: Elliptic Curve Digital Signature Algorithm.

   $ economy of mechanism
      (I) The principle that security mechanism should be designed to be
      as simple as possible, so that it can be correctly implemented and
      so that it can be verified that its operation enforces the
      security policy. (See: least privilege.)

   $ EDI
      See: electronic data interchange.

   $ EDIFACT
      See: (secondary definition in) electronic data interchange.

   $ EE
      (D) ISPDs SHOULD NOT use this abbreviation because of possible
      confusion among "end entity", "end-to-end encryption", "escrowed
      encryption standard", and other terms.

   $ EES
      See: Escrowed Encryption Standard.

   $ El Gamal algorithm
      (N) An algorithm for asymmetric cryptography, invented in 1985 by
      Taher El Gamal, that is based on the difficulty of calculating
      discrete logarithms and can be used for both encryption and
      digital signatures.

   $ electronic codebook (ECB)
      (I) An block cipher mode in which a plaintext block is used
      directly as input to the encryption algorithm and the resultant
      output block is used directly as ciphertext [FP081].

   $ electronic commerce
      (I) General usage: Business conducted through paperless exchanges
      of information, using electronic data interchange, electronic
      funds transfer (EFT), electronic mail, computer bulletin boards,
      facsimile, and other paperless technologies.

      (O) SET usage: "The exchange of goods and services for payment
      between the cardholder and merchant when some or all of the
      transaction is performed via electronic communication." [SET2]




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   $ electronic data interchange (EDI)
      (I) Computer-to-computer exchange, between trading partners, of
      business data in standardized document formats.

      (C) EDI formats have been standardized primarily by ANSI X12 and
      by EDIFACT (EDI for Administration, Commerce, and Transportation),
      an international, UN-sponsored standard primarily used in Europe
      and Asia. These two are aligning to create a single global EDI
      standard.

   $ electronic signature
      (D) ISPDs SHOULD NOT use this term because there is no current
      consensus on its definition. (Instead, see: digital signature.)

   $ elliptic curve cryptography (ECC)
      (I) A type of asymmetric cryptography based on mathematics of
      groups defined by the points on a curve.

      (C) The most efficient implementation of ECC is claimed to be
      stronger per bit of key (against cryptanalysis that uses a brute
      force attack) than any other known form of asymmetric
      cryptography. ECC is based on mathematics different than the kinds
      originally used to define the Diffie-Hellman algorithm and the
      Digital Signature Algorithm. ECC is based on the mathematics of
      groups defined by the points on a curve, where the curve is
      defined by a quadratic equation in a finite field. ECC can be used
      to define an algorithm for key agreement that is an analog of
      Diffie-Hellman and an algorithm for digital signature that is an
      analog of DSA. (See: ECDSA.)

   $ Elliptic Curve Digital Signature Algorithm (ECDSA)
      (N) A standard [A9062] that is the elliptic curve cryptography
      analog of the Digital Signature Algorithm.

   $ emanation
      (I) An signal (electromagnetic, acoustical, or other byproduct)
      that is emitted by a system (through radiation or conductance) as
      a consequence of its operation, and that may contain information.
      (See: TEMPEST.)

   $ emanations security (EMSEC)
      (I) Physical constraints to prevent information compromise through
      signals emanated by a system, particular the application of
      TEMPEST technology to block electromagnetic radiation.

   $ emergency plan
      (D) A synonym for "contingency plan". In the interest of
      consistency, ISPD SHOULD use "contingency plan" instead of
      "emergency plan".

   $ EMSEC
      See: emanations security.


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   $ EMV
      (I) An acronym for "Europay, MasterCard, Visa". Refers to a
      specification for smart cards that are used as payment cards, and
      for related terminals and applications. [EMV1, EMV2, EMV3]

   $ Encapsulating Security Payload (ESP)
      (I) An Internet IPsec protocol [R2406] designed to provide a mix
      of security services--especially data confidentiality service--in
      the Internet Protocol. (See: Authentication Header.)

      (C) ESP may be used alone, or in combination with the IPsec AH
      protocol, or in a nested fashion with tunneling. Security services
      can be provided between a pair of communicating hosts, between a
      pair of communicating security gateways, or between a host and a
      gateway. The ESP header is inserted after the IP header and before
      either the upper layer protocol header (transport mode) or an
      encapsulated IP header (tunnel mode). ESP can provide data
      confidentiality service, data origin authentication service,
      connectionless data integrity service, an anti-replay service, and
      limited traffic flow confidentiality. The set of services depends
      on the placement of the implementation and on options selected
      when the security association is established.

   $ encipher
      (D) ISPDs SHOULD NOT use this term as a synonym for "encrypt".
      However, see the usage note under "encryption".

   $ encipherment
      (D) ISPDs SHOULD NOT use this term as a synonym for "encryption",
      except in special circumstances that are explained in the usage
      discussion under "encryption".

   $ encode
      (I) Use a system of symbols to represent information, which might
      originally have some other representation. (See: decode.)

      (C) Examples include Morse code, ASCII, and BER.

      (D) ISPDs SHOULD NOT use this term as a synonym for "encrypt",
      because encoding is not usually intended to conceal meaning.

   $ encrypt
      (I) Cryptographically transform data to produce ciphertext. (See:
      encryption.)

   $ encryption
      (I) The cryptographic transformation of data (called "plaintext")
      into a form (called "ciphertext") that conceals the data's
      original meaning to prevent it from being known or used. If the
      transformation is reversible, then corresponding reversal process
      is called "decryption", which is a transformation that restores


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      encrypted data to its original state. (See: cryptography.)

      (C) Usage note: For this concept, ISPDs should use the verb "to
      encrypt" (and related variations: encryption, decrypt, and
      decryption). Because of cultural biases, however, some
      international usage, particularly ISO and CCITT standards, avoid
      "to encrypt" and instead use the verb "to encipher" (and related
      variations: encipherment, decipher, decipherment).

      (O) "The cryptographic transformation of data (see: cryptography)
      to produce ciphertext." [I7498 Part 2]

      (C) Usually, the plaintext input to an encryption operation is
      cleartext. But in some cases, the plaintext may be ciphertext that
      was output from another encryption operation. (See:
      superencryption.)

      (C) Encryption and decryption involve a mathematical algorithm for
      transforming data. In addition to the data to be transformed, the
      algorithm has one or more inputs that are control parameters: (a)
      a key value that varies the transformation and, in some cases, (b)
      an initialization value that establishes the starting state of the
      algorithm.

   $ encryption certificate
      (I) A public-key certificate that contains a public key that is
      intended to be used for encrypting data, rather than for verifying
      digital signatures or performing other cryptographic functions.

      C) A v3 X.509 public-key certificate may have a "keyUsage"
      extension that indicates the purpose for which the certified
      public key is intended.

   $ end entity
      (I) A system entity that is the subject of a public-key
      certificate and that is using, or is permitted and able to use,
      the matching private key only for a purpose or purposes other than
      signing a digital certificate; i.e., an entity that is not a CA.

      (D) "A certificate subject which uses its public [sic] key for
      purposes other than signing certificates." [X509]

      (C) ISPDs SHOULD NOT use the X.509 definition, because it is
      misleading and incomplete. First, the X.509 definition should say
      "private key" rather than "public key" because certificates are
      not usefully signed with a public key. Second, the X.509
      definition is weak regarding whether an end entity may or may not
      use the private key to sign a certificate, i.e., whether the
      subject may be a CA. The intent of X.509's authors was that an end
      entity certificate is not valid for use in verifying a signature
      on an X.509 certificate or X.509 CRL. Thus, it would have been
      better for the X.509 definition to have said "only for purposes


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      other than signing certificates".

      (C) Despite the problems in the X.509 definition, the term itself
      is useful in describing applications of asymmetric cryptography.
      The way the term is used in X.509 implies that it was meant to be
      defined, as we have done here, relative to roles that an entity
      (which is associated with an OSI end system) is playing or is
      permitted to play in applications of asymmetric cryptography other
      than the PKI that supports applications.

      (C) Whether a subject can play both CA and non-CA roles, with
      either the same or different certificates, is a matter of policy.
      (See: certification practice statement.) A v3 X.509 public-key
      certificate may have a "basicConstraints" extension containing a
      "cA" value that specifically "indicates whether or not the public
      key may be used to verify certificate signatures".

   $ end system
      (I) An OSI term for a computer that implements all seven layers of
      the OSIRM and may attach to a subnetwork. (In the context of the
      Internet Protocol Suite, usually called a "host".)

   $ end-to-end encryption
      (I) Continuous protection of data that flows between two points in
      a network, provided by encrypting data when it leaves its source,
      leaving it encrypted while it passes through any intermediate
      computers (such as routers), and decrypting only when the data
      arrives at the intended destination. (See: link encryption,
      wiretapping.)

      (C) When two points are separated by multiple communication links
      that are connected by one or more intermediate relays, end-to-end
      encryption enables the source and destination systems to protect
      their communications without depending on the intermediate systems
      to provide the protection.

   $ end user
      (I) General usage: A system entity, usually a human individual,
      that makes of system resources, primarily for application purposes
      as opposed to system management purposes.

      (I) PKI usage: A synonym for "end entity". But the term "end
      entity" is preferred.

   $ entity
      See: system entity.

   $ entrapment
      (I) "The deliberate planting of apparent flaws in a system for the
      purpose of detecting attempted penetrations or confusing an
      intruder about which flaws to exploit." [FP039] (See: honey pot.)



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   $ ephemeral key
      (I) A public key or a private key that is relatively short-lived.

   $ error detection code
      (I) A checksum designed to detect, but not correct, accidental
      (i.e., unintentional) changes in data.

   $ Escrowed Encryption Standard (EES)
      (N) A U.S. Government standard [FP185] that specifies use of a
      symmetric encryption algorithm (SKIPJACK) and a Law Enforcement
      Access Field (LEAF) creation method to implement part of a key
      escrow system that provides for decryption of encrypted
      telecommunications when interception is lawfully authorized.

      (C) Both SKIPJACK and the LEAF are to be implemented in equipment
      used to encrypt and decrypt unclassified, sensitive
      telecommunications data.

   $ ESP
      See: Encapsulating Security Payload.

   $ Estelle
      (N) A language (ISO 9074-1989) for formal specification of
      computer network protocols.

   $ evaluated products list
      (O) General usage: A list of information system equipment items
      that have been evaluated against, and found to be compliant with,
      at particular set of criteria:

      (O) NSA usage: (http://www.radium.ncsc.mil/tpep/epl/) The
      Evaluated Products List contains items that have been evaluated
      against the TCSEC by the NCSC, or against the Common Criteria by
      the NCSC or one of its partner agencies in another county. The
      List forms Chapter 4 of NSA's "Information Systems Security
      Products and Services Catalogue".

   $ evaluated system
      (I) Refers to a system that has been evaluated against security
      criteria such as the TCSEC, or the Common Criteria for Information
      Technology Security Evaluation.

   $ expire
      See: certificate expiration.

   $ exposure
      See: (secondary definition in) threat consequence.

   $ Extensible Authentication Protocol
      (I) A framework that supports multiple, optional authentication
      mechanisms for PPP, including cleartext passwords, challenge-
      response, and arbitrary dialog sequences. [R2284]


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      (C) This protocol is intended for use primarily by a host or
      router that connects to a PPP network server via switched circuits
      or dial-up lines.

   $ extension
      (I) A data item defined for optional inclusion in a v3 X.509
      public-key certificate or a v2 X.509 CRL.

      (C) The formats defined in X.509 can be extended to provide
      methods for associating additional attributes with subjects and
      public keys and for managing a certification hierarchy:

       - "Certificate extension": X.509 defines standard extensions that
         may be included in v3 certificates to provide additional key
         and security policy information, subject and issuer attributes,
         and certification path constraints.

       - "CRL extension": X.509 defines extensions that may be included
         in v2 CRLs to provide additional issuer key and name
         information, revocation reasons and constraints, and
         information about distribution points and delta CRLs.

       - "Private extension": Additional extensions, each named by an
         OID, can be locally defined as needed by applications or
         communities. (See: PKIX private extension, SET private
         extensions.)

   $ extranet
      (I) A computer network that an organization uses to carry
      application data traffic between the organization and its business
      partners. (See: Intranet.)

      (C) An extranet can be implemented securely, either on the
      Internet or using Internet technology, by constructing the
      extranet as a VPN.

   $ failure control
      (I) A methodology used to provide fail-safe or fail-soft
      termination and recovery of functions and processes when failures
      are detected or occur in a system. [FP039]

   $ fail safe
      (I) A mode of system termination that automatically leaves system
      processes and components in a secure state when a failure occurs
      or is detected in the system.

   $ fail soft
      (I) Selective termination of affected non-essential system
      functions and processes when a failure occurs or is detected in
      the system.



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   $ Federal Information Processing Standards (FIPS)
      (N) The Federal Information Processing Standards Publication (FIPS
      PUB) series issued by the U.S. National Institute of Standards and
      Technology as technical guidelines for U.S. Government
      procurements of information processing system equipment and
      services. [FP031, FP039, FP046, FP081, FP113, FP140, FP151, FP180,
      FP185, FP186, FP188]

      (C) Issued under the provisions of section 111(d) of the Federal
      Property and Administrative Services Act of 1949 as amended by the
      Computer Security Act of 1987, Public Law 100-235.

   $ Federal Public-key Infrastructure (FPKI)
      (N) A PKI being planned to establish facilities, specifications,
      and policies needed by the U.S. Federal Government to use public-
      key certificates for INFOSEC, COMSEC, and electronic commerce
      involving unclassified but sensitive applications and interactions
      between Federal agencies as well as with entities of other
      branches of the Federal Government, state, and local governments,
      business, and the public. [FPKI]

   $ Federal Standard 1027
      (N) An obsolete document defining emanation, anti-tamper, security
      fault analysis, and manual key management criteria for DES
      encryption devices, primary for OSI layer 2. Renamed "FIPS PUB
      140" when responsibility for protecting unclassified, sensitive
      information was transferred from NSA to NIST, and then replaced by
      FIPS PUB 140-1.

   $ File Transfer Protocol (FTP)
      (I) A TCP-based, application-level, Internet Standard protocol for
      moving data files from one computer to another. [R0959]

   $ filtering router
      (I) An internetwork router that selectively prevents the passage
      of data packets according to a security policy.

      (C) A filtering router may be used as a firewall or part of a
      firewall. A router usually receives a packet from a network and
      decides where to forward it on a second network. A filtering
      router does the same, but first decides whether the packet should
      be forwarded at all, according to some security policy. The policy
      is implemented by rules (packet filters) loaded into the router.
      The rules mostly involve values of data packet control fields
      (especially IP source and destination addresses and TCP port
      numbers). [R2179]

   $ financial institution
      (N) "An establishment responsible for facilitating customer-
      initiated transactions or transmission of funds for the extension
      of credit or the custody, loan, exchange, or issuance of money."
      [SET2]


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   $ fingerprint
      (I) A pattern of curves formed by the ridges on a fingertip. (See:
      biometric authentication, thumbprint.)

      (D) ISPDs SHOULD NOT use this term as a synonym for "hash result"
      because it mixes concepts in a potentially misleading way.

      (D) ISPDs SHOULD NOT use this term with the following PGP
      definition, because the term and definition mix concepts in a
      potentially misleading way and duplicate the meaning of "hash
      result":

      (C) PGP usage: A hash result used to authenticate a public key
      (key fingerprint) or other data. [PGP]

   $ FIPS
      See: Federal Information Processing Standards.

   $ FIPS PUB 140-1
      (N) A U.S. Government standard [FP140] for security requirements
      to be met by a cryptographic module used to protect unclassified
      information in computer and communication systems. (To be
      superseded by the Common Criteria. Also see: Federal Information
      Processing Standards.)

      (C) The standard specifies four increasing levels (from "Level 1"
      to "Level 4") of requirements to cover a wide range of potential
      applications and environments. The requirements address basic
      design and documentation, module interfaces, authorized roles and
      services, physical security, software security, operating system
      security, key management, cryptographic algorithms,
      electromagnetic interference and electromagnetic compatibility
      (EMI/EMC), and self-testing. NIST and the Canadian Communication
      Security Establishment jointly certify modules.

   $ firewall
      (I) An internetwork gateway that restricts data communication
      traffic to and from a computer network to protect that network's
      system resources against threats from other networks that are
      outside the firewall. (See: guard.)

      (C) A firewall typically separates a smaller, secure network (such
      as a corporate LAN) from a larger network (such as the Internet).
      Installed at the point where the networks connect, the firewall
      applies security policy rules to control traffic that flows in and
      out of the protected network.

      (C) A firewall is not always a single computer. For example, a
      firewall may consist of a pair of filtering routers and one or
      more proxy servers running on one or more bastion hosts, all
      connected to a small, dedicated LAN between the two routers. The


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      external router blocks attacks that use IP to break security (IP
      address spoofing, source routing, packet fragments), while proxy
      servers block attacks that would exploit a vulnerability in a
      higher layer protocol or service. The internal router blocks
      traffic from leaving the protected network except through the
      proxy servers. The difficult part is defining criteria by which
      packets are denied passage through the firewall, because a
      firewall not only needs to keep intruders out, but usually also
      needs to let authorized users in and out.

   $ firmware
      (I) Computer programs and data stored in hardware (typically in
      read-only memory or programmable read-only memory) such that the
      programs and data cannot be dynamically written or modified during
      execution of the programs. (Compare with: hardware, software.)

   $ FIRST
      See: Forum of Incident Response and Security Teams.

   $ flaw hypothesis methodology
      (I) An evaluation or attack technique in which specifications and
      documentation for a system are analyzed to hypothesize flaws in
      the system. The list of hypothetical flaws is prioritized on the
      basis of the estimated probability that a flaw exists and,
      assuming it does, on the ease of exploiting it and the extent of
      control or compromise it would provide. The prioritized list is
      used to direct a penetration test or attack against the system.
      [NCS04]

   $ flooding
      (I) An attack that attempts to cause a failure in (especially, in
      the security of) a computer system or other data processing entity
      by providing more input than the entity can process properly.
      (See: denial of service.)

   $ flow analysis
      (I) An analysis performed on a nonprocedural formal system
      specification that locates potential flows of information between
      system variables. By assigning security levels to the variables,
      the analysis can find some types of covert channels.

   $ flow control
      (I) A procedure or technique to ensure that information transfers
      within a system are not made from a higher security level to a
      lower security level. (See: covert channel, simple security
      property, confinement property.)

   $ formal specification
      (I) A specification of hardware or software functionality in a
      computer-readable language; usually a precise mathematical
      description of the behavior of the system with the providing a
      correctness proof.


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   $ formulary
      (I) A technique for enabling a decision to grant or deny access to
      be made dynamically at the time the access is attempted, rather
      than earlier when an access control list or ticket is created.

   $ FORTEZZA(trademark)
      (N) A registered trademark of the U.S. National Security Agency
      (NSA), used for a family of interoperable security products that
      implement a NIST/NSA-approved suite of cryptographic algorithms
      for digital signature, hash, encryption, and key exchange. The
      products include a PC card that contains a CAPSTONE chip, serial
      port modems, server boards, smart cards, and software
      implementations.

   $ Forum of Incident Response and Security Teams (FIRST)
      (N) An international consortium of CSIRTs that work together to
      handle computer security incidents and promote preventive
      activities. (See: CSIRT, security incident.)

      (C) FIRST was founded in 1990 and, as of September 1999, had
      nearly 70 members spanning the globe. It mission includes:

       - Provide members with technical information, tools, methods,
         assistance, and guidance.
       - Coordinate proactive liaison activities and analytical support.
       - Encourage development of quality products and services.
       - Improve national and international information security for
         government, private industry, academia, and the individual.
       - Enhance the image and status of the CSIRT community.

   $ forward secrecy
      See: public-key forward secrecy.

   $ FPKI
      See: Federal Public-Key Infrastructure.

   $ FTP
      See: File Transfer Protocol.

   $ gateway
      (I) A relay mechanism that attaches to two (or more) computer
      networks that have similar functions but dissimilar
      implementations and that enables host computers on one network to
      communicate with hosts on the other; an intermediate system that
      is the interface between two computer networks. (See: bridge,
      firewall, guard, internetwork, proxy server, router, and
      subnetwork.)

      (C) Gateways are conceivable at any OSI layer, but actual gateways
      operate at OSI layer 3 (see: bridge, router) or OSI layer 7 (see:
      proxy server). When the two networks differ in the protocol by


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      which they offer service to hosts, the gateway may translate one
      protocol into another or otherwise facilitate interoperation of
      hosts (see: Internet Protocol).

   $ GCA
      See: geopolitical certificate authority.

   $ GeneralizedTime
      (N) The ASN.1 data type "GeneralizedTime" (specified in ISO 8601)
      contains a calendar date (YYYYMMDD) and a time of day, which is
      either (a) the local time, (b) the Coordinated Universal Time, or
      (c) both the local time and an offset allowing Coordinated
      Universal Time to be calculated. (See: Coordinated Universal Time,
      UTCTime.)

   $ Generic Security Service Application Program Interface (GSS-API)
      (I) An Internet Standard protocol [R2078] that specifies calling
      conventions by which an application (typically another
      communication protocol) can obtain authentication, integrity, and
      confidentiality security services independently of the underlying
      security mechanisms and technologies, thus allowing the
      application source code to be ported to different environments.

      (C) "A GSS-API caller accepts tokens provided to it by its local
      GSS-API implementation and transfers the tokens to a peer on a
      remote system; that peer passes the received tokens to its local
      GSS-API implementation for processing. The security services
      available through GSS-API in this fashion are implementable (and
      have been implemented) over a range of underlying mechanisms based
      on [symmetric] and [asymmetric cryptography]." [R2078]

   $ geopolitical certificate authority (GCA)
      (O) SET usage: In a SET certification hierarchy, an optional level
      that is certified by a brand certification authority and that may
      certify cardholder CAs, merchant CAs, and payment gateway CAs.
      Using GCAs enables a brand to distribute responsibility for
      managing certificates to geographic or political regions, so that
      brand policies can vary between regions as needed.

   $ Green Book
      (D) Except as an explanatory appositive, ISPDs SHOULD NOT use this
      term as a synonym for "Defense Password Management Guideline"
      [CSC2]. Instead, use the full proper name of the document or, in
      subsequent references, a conventional abbreviation. (See: Rainbow
      Series.)

      (D) Usage note: To improve international comprehensibility of
      Internet Standards and the Internet Standards Process, ISPDs
      SHOULD NOT use "cute" synonyms for document titles. No matter how
      popular and clearly understood a nickname may be in one community,
      it is likely to cause confusion in others. For example, in
      addition to the meaning given above, there are several other


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      information system standards called "the Green Book". The
      following are just a few examples:

       - Any 1992 standard issued by the ITU-T (then CCITT).
       - "PostScript Language Program Design", Adobe Systems, Addison-
         Wesley, 1988.
       - IEEE 1003.1 POSIX Operating Systems Interface.
       - "Smalltalk-80: Bits of History, Words of Advice", Glenn
         Krasner, Addison-Wesley, 1983.
       - "X/Open Compatibility Guide".
       - A particular CD-ROM format developed by Phillips.

   $ GRIP
      (I) A contraction of "Guidelines and Recommendations for Security
      Incident Processing", the name of the IETF working group that
      seeks to facilitate consistent handling of security incidents in
      the Internet community. (See: security incident.)

      (C) Guidelines to be produced by the WG will address technology
      vendors, network service providers, and response teams in their
      roles assisting organizations in resolving security incidents.
      These relationships are functional and can exist within and across
      organizational boundaries.

   $ GSS-API
      See: Generic Security Service Application Program Interface.

   $ guard
      (I) A gateway that is interposed between two networks (or
      computers, or other information systems) operating at different
      security levels (one is usually higher than the other) and is
      trusted to mediate all information transfers between the two
      levels, to either ensure that no sensitive information from the
      first (higher) level can leak to the second (lower) level, or to
      protect against destruction of data on the first (higher) level.
      (See: firewall.)

   $ GULS
      (I) Generic Upper Layer Security service element (ISO 11586), a
      five-part standard for the exchange of security information and
      security-transformation functions that support the integrity and
      confidentiality of application data.

   $ guest login
      See: anonymous login.

   $ hacker
      (I) Someone with a strong interest in computers, who enjoys
      learning about them and experimenting with them. (See: cracker.)

      (C) The recommended definition is the original meaning of the term
      (circa 1960), which then had a neutral or positive connotation.


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      Today, the term is frequently misused, especially by journalists,
      to have the pejorative meaning of cracker.

   $ handle
      (I) (1.) Verb: Perform processing operations on data, such as
      receive and transmit, collect and disseminate, create and delete,
      store and retrieve, read and write, and compare. (2.) A on-line
      pseudonym, such as those used by crackers; derived from citizens
      band radio usage.

   $ hardware
      (I) The physical, material components of a computer system.
      (Compare with: firmware, software.)

   $ hardware token
      See: token.

      (O) SET usage: "A portable device (for example, smart card, and
      PCMCIA cards) specifically designed to store cryptographic
      information and possibly perform cryptographic functions in a
      secure manner." [SET2]

   $ hash code
      (D) ISPDs SHOULD NOT use this term as a synonym for "hash result"
      because it unnecessarily duplicates the meaning of the other term
      and mixes concepts in a potentially misleading way. A hash result
      is not a "code" in the sense defined in this glossary. (See: hash
      value, message digest.)

   $ hash function
      (I) An algorithm that computes a value based on a data set (such
      as a message or file; usually variable-length; possibly very
      large), thereby mapping the data set to a smaller data object
      (called the hash result) which is usually a fixed-size value.
      (See: checksum, keyed hash.)

      (O) "A (mathematical) function which maps values from a large
      (possibly very large) domain into a smaller range. A 'good' hash
      function is such that the results of applying the function to a
      (large) set of values in the domain will be evenly distributed
      (and apparently at random) over the range." [X509]

      (C) The kind of hash function needed for security applications is
      a one-way function called a cryptographic hash function, an
      algorithm for which it is computationally infeasible (because no
      attack is significantly more efficient than brute force) to find
      either (a) a data set that maps to a pre-specified hash result
      (the "one-way" property) or (b) two data sets that map to the same
      hash result (the "collision-free" property). (See: MD2, MD4, MD5,
      SHA-1.)

      (C) A cryptographic hash is "good" in the sense stated above by


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      X.509. Any change to an input data set will, with high
      probability, result in a different hash result, so that the result
      of a cryptographic hash makes a good checksum for a data set.

   $ hash result
      (I) The output of a hash function.

      (O) "The output produced by a hash function upon processing a
      message" (where "message" is broadly defined as "a digital
      representation of data"). [ABA] (The recommended definition is
      compatible with this ABA definition, but we avoid the unusual
      definition of "message".)

   $ hash value
      (D) ISPDs SHOULD NOT use this term as a synonym for "hash result"
      (the output of a hash function) because it might be confused with
      "hashed" value (the input to a hash function). (See: hash code,
      message digest.)

   $ hierarchical PKI
      (I) A PKI architecture based on a certification hierarchy. (See:
      mesh PKI, trust-file PKI.)

   $ hierarchy management
      (I) The process of generating configuration data and issuing
      public-key certificates to build and operate a certification
      hierarchy.

   $ hierarchy of trust
      (D) ISPDs SHOULD NOT use this term as a synonym for "certification
      hierarchy" because this term mixes concepts in a potentially
      misleading way and duplicates the meaning of another, standardized
      term. (See: trust, web of trust.)

   $ hijack attack
      (I) A form of active wiretapping in which the attacker seizes
      control of a previously established communication association.
      (See: man-in-the-middle attack, pagejacking, piggyback attack.)

   $ HMAC
      (I) A keyed hash [R2104] that can be based on any interactive
      cryptographic hash (e.g., MD5 or SHA-1), so that the cryptographic
      strength of HMAC depends on the properties of the selected
      cryptographic hash. (See: [R2202, R2403, R2404].)

      (C) Assume that H is a generic cryptographic hash in which a basic
      compression function is interated on data blocks of length B
      bytes. L is the length of the of hash result of H. K is a secret
      key of length L <= K <= B. The values IPAD and OPAD are fixed
      strings used as inner and outer padding and defined as follows:
      IPAD = the byte 0x36 repeated B times, OPAD = the byte 0x5C
      repeated B times. HMAC is computed by H(K XOR OPAD, H(K XOR IPAD,


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      inputdata)).

      (C) The goals of HMAC are as follows:

       - To use available cryptographic hash functions without
         modification, particularly those that perform well in software
         and for which software is freely and widely available.
       - To preserve the original performance of the selected hash
         without significant degradation.
       - To use and handle keys in a simple way.
       - To have a well-understood cryptographic analysis of the
         strength of the mechanism based on reasonable assumptions about
         the underlying hash function.
       - To enable easy replacement of the hash function in case a
         faster or stronger hash is found or required.

   $ honey pot
      (I) A system (e.g., a web server) or a system resource (e.g., a
      file on a server), that is designed to be attractive to potential
      crackers and intruders, like honey is attractive to bears. (See:
      entrapment.)

      (D) It is likely that other cultures have different metaphors for
      this concept. To ensure international understanding, this term
      SHOULD NOT be used unless it is locally accompanied by this
      definition. (See: (usage note under) Green Book.)

   $ host
      (I) A computer that is attached to a communication subnetwork or
      internetwork and can use services provided by the network to
      exchange data with other attached systems. (Compare with: end
      system.) In the context of the Internet protocol suite, a term for
      a networked computer that does not forward Internet Protocol
      packets that are not addressed to the computer itself. (Compare
      with: router.)

      (C) Derivation: As viewed by its users, a host "entertains"
      guests, providing application layer services or access to other
      computers attached to the network. Although some traditional
      peripheral service devices, such as printers, can now be
      independently connected to networks, they are not usually called
      hosts.

   $ HTML
      See: Hypertext Markup Language.

   $ HTTP
      See: Hypertext Transfer Protocol.

   $ https
      (I) When used in the first part of a URL (the part that precedes
      the colon and that specifies an access scheme or protocol), this


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      term specifies the use of HTTP enhanced by a security mechanism,
      normally SSL. (Compare with: S-HTTP.)

   $ hybrid encryption
      (I) An application of cryptography that combines two or more
      encryption algorithms, particularly a combination of symmetric and
      asymmetric encryption (e.g., see: digital envelope).

      (C) Asymmetric algorithms require more computation than
      equivalently strong symmetric ones. Thus, asymmetric encryption is
      not normally used for data confidentiality except in distributing
      symmetric keys in applications where the key data is usually short
      (in terms of bits) compared to the data it protects. (For example,
      see: MSP, PEM, PGP.)

   $ hyperlink
      (I) In hypertext or hypermedia, an information object (such as a
      word, a phrase, or an image; usually highlighted by color or
      underscoring) that points (indicates how to connect) to related
      information that is located elsewhere and can be retrieved by
      activating the link (such as by selecting the object with a mouse
      pointer and clicking).

   $ hypermedia
      (I) A generalization of hypertext; any media that contain
      hyperlinks, which point to additional material in the same or
      another data object.

   $ hypertext
      (I) A computer document, or part of a document, that contains
      hyperlinks to other documents; i.e., text that contains active
      pointers to other text. Usually written in Hypertext Markup
      Language and accessed using a web browser. (See: hypermedia.)

   $ Hypertext Markup Language (HTML)
      (I) A platform-independent system of syntax and semantics for
      adding characters to data files (particularly text files) to
      represent the data's structure and to point to related data, thus
      creating hypertext for use in the World Wide Web and other
      applications. [R1866]

   $ Hypertext Transfer Protocol (HTTP)
      (I) An application-level, client-server, Internet protocol used to
      carry data requests and responses in the World Wide Web [R2068].
      (See: hypertext.)

   $ IAB
      See: Internet Architecture Board.

   $ IANA
      See: Internet Assigned Numbers Authority.



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   $ ICMP
      See: Internet Control Message Protocol.

   $ ICMP flood
      (I) A denial of service attack that sends a host more ICMP echo
      request ("ping") packets than the protocol implementation can
      handle. (See: flooding, smurf.)

   $ ICRL
      See: indirect certificate revocation list.

   $ IDEA
      See: International Data Encryption Algorithm.

   $ identification
      (I) An act or process that presents an identifier to a system so
      that the system can recognize a system entity and distinguish it
      from other entities. (See: authentication.)

   $ Identification Protocol
      (I) An client-server Internet protocol [R1413] for learning the
      identity of a user of a particular TCP connection.

      (C) Given a TCP port number pair, the server returns a character
      string that identifies the owner of that connection on the
      server's system. The protocol is not intended for authorization or
      access control. At best, it provides additional auditing
      information with respect to TCP.

   $ identity-based security policy
      (I) "A security policy based on the identities and/or attributes
      of users, a group of users, or entities acting on behalf of the
      users and the resources/objects being accessed." [I7498 Part 2]
      (See: rule-based security policy.)

   $ IEEE
      See: Institute of Electrical and Electronics Engineers, Inc.

   $ IEEE 802.10
      (N) An IEEE committee developing security standards for local area
      networks; see: SILS.

   $ IEEE P1363
      (N) An IEEE working group, Standard for Public-Key Cryptography,
      developing a comprehensive reference standard for asymmetric
      cryptography; covering discrete logarithm (e.g., DSA), elliptic
      curve, and integer factorization (e.g., RSA); and covering key
      agreement, digital signature, and encryption.

   $ IESG
      See: Internet Engineering Steering Group.



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   $ IETF
      See: Internet Engineering Task Force.

   $ IKE
      See: IPsec Key Exchange.

   $ IMAP4
      See: Internet Message Access Protocol, version 4.

   $ IMAP4 AUTHENTICATE
      (I) A IMAP4 "command" (better described as a transaction type, or
      a protocol-within-a-protocol) by which an IMAP4 client optionally
      proposes a mechanism to an IMAP4 server to authenticate the client
      to the server and provide other security services. (See: POP3.)

      (C) If the server accepts the proposal, the command is followed by
      performing a challenge-response authentication protocol and,
      optionally, negotiating a protection mechanism for subsequent POP3
      interactions. The security mechanisms used by IMAP4 AUTHENTICATE--
      including Kerberos, GSSAPI, and S/Key--are described in [R1731].

   $ in the clear
      (I) Not encrypted. (See: cleartext.)

   $ indirect certificate revocation list (ICRL)
      (I) In X.509, a CRL that may contain certificate revocation
      notifications for certificates issued by CAs other than the issuer
      of the list.

   $ indistinguishability
      (I) An attribute of an encryption algorithm that is a
      formalization of the notion that the encryption of some string is
      indistinguishable from the encryption of an equal-length string of
      nonsense.

      (C) Under certain conditions, this notion is equivalent to
      semantic security.

   $ information
      (I) Facts and ideas, which can be represented (encoded) as various
      forms of data.

   $ Information Technology Security Evaluation Criteria (ITSEC)
      (N) Standard developed for use in the European Union; accommodates
      a wider range of security assurance and functionality combinations
      than the TCSEC. Superseded by the Common Criteria. [ITSEC]

   $ INFOSEC
      (I) Abbreviation for "information security", referring to security
      measures that implement and assure security services in computer
      systems (i.e., COMPUSEC) and communication systems (i.e., COMSEC).



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   $ initialization value (IV)
      (I) An input parameter that sets the starting state of a
      cryptographic algorithm or mode. (Sometimes called "initialization
      vector" or "message indicator".)

      (C) An IV can be used to introduce cryptographic variance in
      addition to that provided by a key (see: salt), and to synchronize
      one cryptographic process with another. For an example of the
      latter, cipher block chaining mode requires an IV [R2405].

   $ initialization vector
      (D) A synonym for "initialization value". In the interest of
      consistency, ISPDs SHOULD use initialization value" instead of
      "initialization vector".

   $ insider attack
      See: (secondary definition in) attack.

   $ Institute of Electrical and Electronics Engineers, Inc. (IEEE)
      (N) The IEEE is a not-for-profit association of more than 330,000
      individual members in 150 countries. The IEEE produces 30 percent
      of the world's published literature in electrical engineering,
      computers, and control technology; holds annually more than 300
      major conferences; and has more than 800 active standards with 700
      under development. (See: Standards for Interoperable LAN/MAN
      Security.)

   $ integrity
      See: data integrity, correctness integrity, source integrity,
      system integrity.

   $ integrity check
      (D) ISPDs SHOULD NOT use this term as a synonym for "cryptographic
      hash" or "protected checksum", because this term unnecessarily
      duplicates the meaning of other, well-established terms.

   $ intelligent threat
      (I) A circumstance in which an adversary has the technical and
      operational capability to detect and exploit a vulnerability and
      also has the demonstrated, presumed, or inferred intent to do so.
      (See: threat.)

   $ International Data Encryption Algorithm (IDEA)
      (N) A patented, symmetric (see: symmetric cryptography) block
      cipher that uses a 128-bit key and operates on 64-bit blocks.
      [Schn]

   $ International Standard
      See: (secondary definition in) ISO.

   $ International Traffic in Arms Regulations (ITAR)
      (N) Rules issued by the U.S. State Department, by authority of the


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      Arms Export Control Act (22 U.S.C. 2778), to control export and
      import of defense articles and defense services, including
      information security systems, such as cryptographic systems, and
      TEMPEST suppression technology. (See: Wassenaar Arrangement.)

   $ internet
   $ Internet
      See: internet vs. Internet.

   $ Internet Architecture Board (IAB)
      (I) A technical advisory group of the ISOC, chartered by the ISOC
      Trustees to provide oversight of Internet architecture and
      protocols and, in the context of Internet Standards, a body to
      which decisions of the IESG may be appealed. Responsible for
      approving appointments to the IESG from among nominees submitted
      by the IETF nominating committee. [R2026]

   $ Internet Assigned Numbers Authority (IANA)
      (I) Since the early days of the Internet, the IANA has been
      chartered by the ISOC and the Federal Network Council to be the
      central coordination, allocation, and registration body for
      parameters for Internet protocols. Now, a new not-for-profit
      organization is being proposed, with an international board of
      directors to oversee the operations of the necessary central
      coordinating functions of the Internet.

      (C) The Internet protocol suite, as defined by the IETF and the
      IESG, contains numerous parameters, such as internet addresses,
      domain names, autonomous system numbers, protocol numbers, port
      numbers, management information base object identifiers, including
      private enterprise numbers, and many others. The Internet
      community requires that the values used in these parameter fields
      be assigned uniquely. The IANA makes those assignments as
      requested and maintains a registry of the current values.

   $ Internet Control Message Protocol (ICMP)
      (I) An Internet Standard protocol [R0792] that is used to report
      error conditions during IP datagram processing and to exchange
      other information concerning the state of the IP network.

   $ Internet Draft
      (I) A working document of the IETF, its areas, and its working
      groups. (Other groups may also distribute working documents as
      Internet Drafts.) An Internet Draft is not an archival document
      like an RFC is. Instead, an Internet Draft is a preliminary or
      working document that is valid for a maximum of six months and may
      be updated, replaced, or made obsolete by other documents at any
      time. It is inappropriate to use an Internet Draft as reference
      material or to cite it other than as "work in progress."

   $ Internet Engineering Steering Group (IESG)
      (I) The part of the ISOC responsible for technical management of


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      IETF activities and administration of the Internet Standards
      Process according to procedures approved by the ISOC Trustees.
      Directly responsible for actions along the "standards track",
      including final approval of specifications as Internet Standards.
      Composed of IETF Area Directors and the IETF chairperson, who also
      chairs the IESG. [R2026]

   $ Internet Engineering Task Force (IETF)
      (I) A self-organized group of people who make contributions to the
      development of Internet technology. The principal body engaged in
      developing Internet Standards, although not itself a part of the
      ISOC. Composed of Working Groups, which are arranged into Areas
      (such as the Security Area), each coordinated by one or more Area
      Directors. Nominations to the IAB and the IESG are made by a
      committee selected at random from regular IETF meeting attendees
      who have volunteered. [R2026, R2323]

   $ Internet Message Access Protocol, version 4 (IMAP4)
      (I) A Internet protocol [R2060] by which a client workstation can
      dynamically access a mailbox on a server host to manipulate and
      retrieve mail message that the server has received and is holding
      for the client. (See: POP3.)

      (C) IMAP4 has mechanisms for optionally authenticating a client to
      a server and providing other security services. (See: IMAP4
      AUTHENTICATE.)

   $ Internet Policy Registration Authority (IPRA)
      (I) An X.509-compliant CA that is the top CA of the Internet
      certification hierarchy operated under the auspices of the ISOC
      [R1422]. (See: (PEM usage under) certification hierarchy.)

   $ Internet Protocol (IP)
      (I) A TCP/IP protocol that moves datagrams (discrete sets of bits)
      from one computer to another across an internetwork but does not
      provide reliable delivery, flow control, sequencing, or other end-
      to-end services that TCP provides. (Includes both version 4
      [R0791] and version 6 [R2460].) (See: IP address.)

      (C) In the OSIRM, IP would be placed at the top of the layer 3.

   $ Internet Protocol security (IPsec)
      (I) (1.) The name of the IETF working group that is specifying a
      security architecture [R2401] and protocols to provide security
      services for Internet Protocol traffic. (Implementation is
      optional for IP version 4, mandatory for version 6.) (2.) A
      collective name for that architecture and set of protocols. (See:
      Internet Protocol Security Option.)

      (C) Note that the letters "sec" are lower-case.

      (C) The IPsec architecture specifies (a) security protocols (AH


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      and ESP), (b) security associations (what they are, how they work,
      how they are managed, and associated processing), (c) key
      management (IKE), and (d) algorithms for authentication, and
      encryption. The set of security services include access control
      service, connectionless data integrity service, data origin
      authentication service, protection against replays (detection of
      the arrival of duplicate datagrams, within a constrained window),
      data confidentiality service, and limited traffic flow
      confidentiality.

   $ Internet Protocol Security Option (IPSO)
      (I) Refers to one of three types of optional additions to IP
      datagrams. ISPDs SHOULD NOT use this term without a modifier to
      identify which type is meant. (See: IPsec.)

       - "DoD Basic Security Option" (IP option type 130): Defined for
      use on U.S. Department of Defense common user data networks.
      Identifies the U.S. classification level at which the datagram
      is to be protected and the protection authorities whose rules
      apply to the datagram. [R1108]

         A "protection authority" is a National Access Program (e.g.,
      GENSER, SIOP-ESI, SCI, NSA, Department of Energy) or Special
      Access Program that specifies protection rules for transmission
      and processing of the information contained in the datagram.
      [R1108]

       - "DoD Extended Security Option" (IP option type 133): Permits
      additional security labeling information, beyond that present
      in the Basic Security Option, to be supplied in the datagram to
      meet the needs of registered authorities. [R1108]

       - "Common IP Security Option" (CIPSO) (IP option type 134):
      Designed by TSIG to carry hierarchic and non-hierarchic
      security labels. (Formerly called "Commercial IP Security
      Option".) Was published as Internet-Draft [CIPSO]; not advanced
      to RFC.

   $ Internet protocol suite
      See: (secondary definition in) Internet.

   $ Internet Security Association and Key Management Protocol (ISAKMP)
      (I) An Internet IPsec protocol [R2408] to negotiate, establish,
      modify, and delete security associations, and to exchange key
      generation and authentication data, independent of the details of
      any specific key generation technique, key establishment protocol,
      encryption algorithm, or authentication mechanism.

      (C) ISAKMP supports negotiation of security associations for
      protocols at all TCP/IP layers. By centralizing management of
      security associations, ISAKMP reduces duplicated functionality
      within each protocol. ISAKMP can also reduce connection setup


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      time, by negotiating a whole stack of services at once. Strong
      authentication is required on ISAKMP exchanges, and a digital
      signature algorithm based on asymmetric cryptography is used
      within ISAKMP's authentication component.

   $ Internet Society (ISOC)
      (I) A professional society concerned with Internet development
      (including technical Internet Standards); with how the Internet is
      and can be used; and with social, political, and technical issues
      that result. The ISOC Board of Trustees approves appointments to
      the IAB from among nominees submitted by the IETF nominating
      committee. [R2026]

   $ Internet Standard
      (I) A specification, approved by the IESG and published as an RFC,
      that is stable and well-understood, is technically competent, has
      multiple, independent, and interoperable implementations with
      substantial operational experience, enjoys significant public
      support, and is recognizably useful in some or all parts of the
      Internet. [R2026] (See: RFC.)

      (C) The Internet Standards Process is an activity of the ISOC and
      is organized and managed by the IAB and the IESG. The process is
      concerned with all protocols, procedures, and conventions used in
      or by the Internet, whether or not they are part of the Internet
      Protocol Suite. (See: (secondary definition in) Internet.) The
      "Internet Standards Track" has three levels of increasing
      maturity: Proposed Standard, Draft Standard, and Standard.
      (Compare with: (levels in) ISO.)

   $ Internet Standards Process document (ISPD)
      (C) For convenience, this Glossary uses this term to refer to an
      RFC or an Internet-Draft that is produced as part of that process.
      However, neither the term nor the abbreviation is widely accepted
      and, therefore, SHOULD NOT be used in an ISPD unless it is locally
      accompanied by a definition equivalent to this one. (See: Internet
      Standard.)

   $ internet vs. Internet
      1. (I) Not capitalized: The term "internet" is a popular short
      synonym for "internetwork".

      2. (I) Capitalized: "The Internet" is the single, interconnected,
      worldwide system of commercial, government, educational, and other
      computer networks that share the protocol suite and the name and
      address spaces that are specified by the IAB [R2026].

      (C) The suite is called the "Internet protocol suite" (IPS), but
      also is popularly know as "TCP/IP", because TCP and IP are two of
      its fundamental protocols. The IPS makes it possible for users of
      any one of the networks in the Internet to communicate with, or
      use the services located on, any of the other networks.


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      (C) Although the Internet does have architectural principles
      [R1958], no Internet Standard defines a layered reference model
      for the IPS that is similar to the OSIRM. However, Internet
      community documents do refer (inconsistently) to layers:
      application, socket, transport, internetwork, network, data link,
      and physical. In this Glossary, Internet layers are referred to by
      name to avoid confusing them with OSIRM layers, which are referred
      to by number.

   $ internetwork
      (I) A system of interconnected networks; a network of networks.
      Usually shortened to "internet". (See: internet vs. Internet.)

      (C) An internet is usually built using OSI layer 3 gateways to
      connect a set of subnetworks. When the subnetworks differ in the
      OSI layer 3 protocol service they provide, the gateways sometimes
      implement a uniform internetwork protocol (e.g., IP) that operates
      at the top of layer 3 and hides the underlying heterogeneity from
      hosts that use communication services provided by the internet.
      (See: router.)

   $ intranet
      (I) A computer network, especially one based on Internet
      technology, that an organization uses for its own internal, and
      usually private, purposes and that is closed to outsiders. (See:
      extranet, virtual private network.)

   $ intruder
      (I) An entity that gains, or attempts to gain, access to a system
      (or system resource) without having authorization to do so. (See:
      cracker.)

   $ intrusion
      See: security intrusion.

   $ intrusion detection
      (I) A security service that monitors and analyzes system events
      for the purpose of noticing, and providing real-time or near real-
      time warning of, attempts to access system resources in an
      unauthorized manner.

   $ invalidity date
      (N) An X.509 CRL entry extension that "indicates the date at which
      it is known or suspected that the [revoked certificate's private
      key] was compromised or that the certificate should otherwise be
      considered invalid" [X509].

      (C) This date may be earlier than the revocation date in the CRL
      entry, and may even be earlier than the date of issue of earlier
      CRLs. However, the invalidity date is not, by itself, sufficient
      for purposes of non-repudiation service. For example, to


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      fraudulently repudiate a validly-generated signature, a private
      key holder may falsely claim that the key was compromised some
      time in the past.

   $ IP
      See: Internet Protocol.

   $ IP address
      (I) The (internetwork) address assigned to a networked computer
      for use by the Internet Protocol.

      (C) An IP version 4 [R0791] address is written as a series of four
      8-bit numbers separated by periods. For example, the address of
      the host named "rosslyn.bbn.com" is 192.1.7.10. For IP version 6
      [R2373], the preferred form is x:x:x:x:x:x:x:x, where the "x"s are
      the hexadecimal values of the eight 16-bit parts of the address.
      For example, FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 and
      1080:0:0:0:8:800:200C:417A.

   $ IP Security Option
      See: Internet Protocol Security Option.

   $ IPRA
      See: Internet Policy Registration Authority.

   $ IPsec
      See: Internet Protocol security.

   $ IPSO
      See: Internet Protocol Security Option.

   $ IPsec Key Exchange (IKE)
      (I) An Internet, IPsec, key-establishment protocol [R2409] (partly
      based on OAKLEY) that is intended for obtaining authenticated
      keying material for use with ISAKMP and for other security
      associations, such as in AH and ESP.

   $ ISAKMP
      See: Internet Security Association and Key Management Protocol.

   $ ISO
      (I) International Organization for Standardization, a voluntary,
      non-treaty, non-government organization, established in 1947, with
      voting members that are designated standards bodies of
      participating nations and non-voting observer organizations. (See:
      ANSI, ITU-T.)

      (C) Legally, ISO is a Swiss, non-profit, private organization. ISO
      and the IEC (the International Electrotechnical Commission) form
      the specialized system for worldwide standardization. (ISO is a
      class D member of ITU-T.) National bodies that are members of ISO
      or IEC participate in developing international standards through


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      ISO and IEC technical committees that deal with particular fields
      of activity. (ANSI is the U.S. voting member of ISO.) Other
      international organizations, governmental and non-governmental, in
      liaison with ISO and IEC, also take part. In information
      technology, ISO and IEC have a joint technical committee, ISO/IEC
      JTC 1.

      (C) The ISO standards development process has four levels of
      increasing maturity: Working Draft (WD), Committee Draft (CD),
      Draft International Standard (DIS), and International Standard
      (IS). DISs adopted by JTC 1 are circulated to national bodies for
      voting, and publication as an IS requires approval by at least 75%
      of the national bodies casting a vote. (Compare with: (levels in)
      Internet Standard.)

   $ ISOC
      See: Internet Society.

   $ ISPD
      See: Internet Standards Process document.

   $ issue (a digital certificate or CRL)
      (I) Generate and sign a digital certificate (or CRL) and, usually,
      distribute it and make it available to potential certificate users
      (or CRL users). (See: certificate creation.)

      (C) The ABA Guidelines [ABA] explicitly limit this term to
      certificate creation, and exclude the act of publishing. In
      general usage, however, "issuing" a digital certificate (or CRL)
      includes not only certificate creation but also making it
      available to potential users, such as by storing it in a
      repository or other directory or otherwise publishing it.

   $ issuer
      1. (I) "Issuer" of a certificate or CRL: The CA that signs a
      digital certificate or CRL.

      (C) An X.509 certificate always includes the issuer's name. The
      name may include a common name value.

      2. (N) "Issuer" of a payment card: SET usage: "The financial
      institution or its agent that issues the unique primary account
      number to the cardholder for the payment card brand." [SET2]

      (C) The institution that establishes the account for a cardholder
      and issues the payment card also guarantees payment for authorized
      transactions that use the card in accordance with card brand
      regulations and local legislation. [SET1]

   $ ITAR
      See: International Traffic in Arms Regulations.



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   $ ITSEC
      See: Information Technology System Evaluation Criteria.

   $ ITU-T
      (N) International Telecommunications Union--Telecommunication
      Standardization Sector (formerly "CCITT"), a United Nations treaty
      organization that is composed mainly of postal, telephone, and
      telegraph authorities of the member countries and that publishes
      standards called "Recommendations". (See: X.400, X.500.)

      (C) The Department of State represents the United States. ITU-T
      works on many kinds of communication systems. ITU-T cooperates
      with ISO on communication protocol standards, and many
      Recommendations in that area are also published as an ISO standard
      with and ISO name and number.

   $ IV
      See: initialization value.

   $ KDC
      See: Key Distribution Center.

   $ KEA
      See: Key Exchange Algorithm.

   $ KEK
      See: key-encrypting key.

   $ Kerberos
      (N) A system developed at the Massachusetts Institute of
      Technology that depends on passwords and symmetric cryptography
      (DES) to implement a ticket-based, peer entity authentication
      service and access control service distributed in a client-server
      network environment. [R1510, Stei]

      (C) Kerberos was developed by Project Athena and is named for the
      three-headed dog guarding Hades.

   $ key
      See: cryptographic key.

   $ key agreement (algorithm or protocol)
      (I) A key establishment method (especially one involving
      asymmetric cryptography) by which two or more entities, without
      prior arrangement except a public exchange of data (such as public
      keys), can each compute the same value, i.e., each independently
      generate the same secret key, that becomes known to both of them
      but cannot be computed by other entities. (Compare with: key
      transport. Also see: Diffie-Hellman, Key Exchange Algorithm.)

      (O) "A method for negotiating a key value on line without
      transferring the key, even in an encrypted form, e.g., the Diffie-


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      Hellman technique." [X509]

      (O) "The procedure whereby two different parties generate shared
      symmetric keys such that any of the shared symmetric keys is a
      function of the information contributed by all legitimate
      participants, so that no party can predetermine the value of the
      key." [A9042]

   $ key authentication
      (N) "The assurance of the legitimate participants in a key
      agreement that no non-legitimate party possesses the shared
      symmetric key." [A9042]

   $ key center
      (I) A centralized key distribution process (used in symmetric
      cryptography), usually a separate computer system, that uses key-
      encrypting keys (master keys) to encrypt and distribute session
      keys needed in a community of users.

      (C) An ANSI standard [A9017] defines two types of key center: key
      distribution center and key translation center.

   $ key confirmation
      (N) "The assurance of the legitimate participants in a key
      establishment protocol that the intended parties sharing the
      symmetric key actually possess the shared symmetric key." [A9042]

   $ key distribution
      (I) A process that delivers a cryptographic key from the location
      where it is generated to the locations where it is used in a
      cryptographic algorithm. (See: key management.)

   $ key distribution center (KDC)
      (I) A type of key center (used in symmetric cryptography) that
      implements a key distribution protocol to provide keys (usually,
      session keys) to two (or more) entities that wish to communicate
      securely. (See: key translation center.)

      (C) A KDC distributes keys to Alice and Bob, who (a) wish to
      communicate with each other but do not currently share keys, (b)
      each share a KEK with the KDC, and (c) may not be able to generate
      or acquire keys by themselves. Alice requests the keys from the
      KDC. The KDC generates or acquires the keys and makes two
      identical sets. The KDC encrypts one set in the KEK it shares with
      Alice, and sends that encrypted set to Alice. The KDC encrypts the
      second set in the KEK it shares with Bob, and either sends that
      encrypted set to Alice for her to forward to Bob, or sends it
      directly to Bob (although the latter option is not supported in
      the ANSI standard [A9017]).

   $ key encapsulation
      See: (secondary definition in) key recovery.


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   $ key-encrypting key (KEK)
      (I) A cryptographic key that is used to encrypt other keys, either
      DEKs or other KEKs, but usually is not used to encrypt application
      data.

   $ key escrow
      See: (secondary definition in) key recovery.

   $ key establishment (algorithm or protocol)
      (I) A process that combines the key generation and key
      distribution steps needed to set up or install a secure
      communication association. (See: key agreement, key transport.)

      (O) "The procedure to share a symmetric key among different
      parties by either key agreement or key transport." [A9042]

      (C) Key establishment involves either key agreement or key
      transport. In key transport, one entity does the key generation
      and then securely sends the secret key to the other entity. (Or
      each entity can generate a key and send it to the other entity,
      where the two keys are combined to form a session key.) For
      example, a message originator can generate a random session key
      and then use the Rivest-Shamir-Adleman algorithm to encrypt that
      key with the public key of the intended recipient. In key
      agreement, the session key is not sent from one entity to another.
      Instead, both entities, without prior arrangement except a public
      exchange of data, each compute the same value; i.e., each
      independently generates the same secret value, which cannot be
      computed by third parties. For example, a message originator and
      the intended recipient can each use their own private key and the
      other's public key in the Diffie-Hellman algorithm to compute a
      shared secret value, which then is used to derive a key to encrypt
      the message.

   $ Key Exchange Algorithm (KEA)
      (N) A key agreement algorithm that is similar to the Diffie-
      Hellman algorithm, uses 1024-bit asymmetric keys, and was
      developed and formerly classified at the "Secret" level by NSA.
      (See: CAPSTONE, CLIPPER, FORTEZZA, SKIPJACK.)

      (C) On 23 June 1998, the NSA announced that KEA had been
      declassified.

   $ key generator
      (I) A device or algorithm that uses mathematical rules to
      deterministically produce a pseudo-random sequence of
      cryptographic keys.

   $ key generation
      (I) A process that creates the sequence of symbols that comprise a
      cryptographic key. (See: key management.)


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   $ key length
      (I) The number of symbols (usually bits) needed to be able to
      represent any of the possible values of a cryptographic key.

   $ key lifetime
      (N) MISSI usage: An attribute of a MISSI key pair that specifies a
      time span that bounds the validity period of any MISSI X.509
      public-key certificate that contains the public component of the
      pair. (See: cryptoperiod.)

   $ key management
      (I) The process of handling and controlling cryptographic keys and
      related material (such as initialization values) during their life
      cycle in a cryptographic system, including ordering, generating,
      distributing, storing, loading, escrowing, archiving, auditing,
      and destroying the material. (See: key distribution, key escrow,
      public-key infrastructure.)

      (O) "The generation, storage, distribution, deletion, archiving
      and application of keys in accordance with a security policy."
      [I7498 Part 2]

      (O) "The activities involving the handling of cryptographic keys
      and other related security parameters (e.g., IVs, counters) during
      the entire life cycle of the keys, including their generation,
      storage, distribution, entry and use, deletion or destruction, and
      archiving." [FP140]

   $ Key Management Protocol (KMP)
      (N) A protocol to establish a shared symmetric key between a pair
      (or a group) of users. (One version of KMP was developed by SDNS,
      and another by SILS.)

   $ key material identifier (KMID)
      (N) MISSI usage: A 64-bit identifier that is assigned to a key
      pair when the public key is bound in a MISSI X.509 public-key
      certificate.

   $ key pair
      (I) A set of mathematically related keys--a public key and a
      private key--that are used for asymmetric cryptography and are
      generated in a way that makes it computationally infeasible to
      derive the private key from knowledge of the public key (e.g.,
      see: Diffie-Hellman, Rivest-Shamir-Adleman).

      (C) A key pair's owner discloses the public key to other system
      entities so they can use the key to encrypt data, verify a digital
      signature, compute a protected checksum, or generate a key in a
      key agreement algorithm. The matching private key is kept secret
      by the owner, who uses it to decrypt data, generate a digital
      signature, verify a protected checksum, or generate a key in a key


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      agreement algorithm.

   $ key recovery
      1. (I) A process for learning the value of a cryptographic key
      that was previously used to perform some cryptographic operation.
      (See: cryptanalysis.)

      2. (I) Techniques that provide an intentional alternate (or
      secondary) means to access the key used for data confidentiality
      service in an encrypted association. [DOD98]

      (C) We assume that the encryption mechanism has a primary means of
      obtaining the key through a key establishment algorithm or
      protocol. For the secondary means, there are two classes of key
      recovery techniques--key escrow and key encapsulation:

       - "Key escrow": A key recovery technique for storing knowledge of
         a cryptographic key or parts thereof in the custody of one or
         more third parties called "escrow agents", so that the key can
         be recovered and used in specified circumstances.

         Key escrow is typically implemented with split knowledge
         techniques. For example, the Escrowed Encryption Standard
         [FP185] entrusts two components of a device-unique split key to
         separate escrow agents. The agents provide the components only
         to someone legally authorized to conduct electronic
         surveillance of telecommunications encrypted by that specific
         device. The components are used to reconstruct the device-
         unique key, and it is used to obtain the session key needed to
         decrypt communications.

       - "Key encapsulation": A key recovery technique for storing
         knowledge of a cryptographic key by encrypting it with another
         key and ensuring that that only certain third parties called
         "recovery agents" can perform the decryption operation to
         retrieve the stored key.

         Key encapsulation typically allows direct retrieval of the
         secret key used to provide data confidentiality.

   $ key space
      (I) The range of possible values of a cryptographic key; or the
      number of distinct transformations supported by a particular
      cryptographic algorithm. (See: key escrow.)

   $ key translation center
      (I) A type of key center (used in a symmetric cryptography) that
      implements a key distribution protocol to convey keys between two
      (or more) parties who wish to communicate securely. (See: key
      distribution center.)

      (C) A key translation center translates keys for future


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      communication between Bob and Alice, who (a) wish to communicate
      with each other but do not currently share keys, (b) each share a
      KEK with the center, and (c) have the ability to generate or
      acquire keys by themselves. Alice generates or acquires a set of
      keys for communication with Bob. Alice encrypts the set in the KEK
      she shares with the center and sends the encrypted set to the
      center. The center decrypts the set, reencrypts the keys in the
      KEK it shares with Bob, and either sends that encrypted set to
      Alice for her to forward to Bob, or sends it directly to Bob
      (although this direct distribution is not supported in the ANSI
      standard [A9017]).

   $ key transport (algorithm or protocol)
      (I) A key establishment method by which a secret key is generated
      by one entity in a communication association and securely sent to
      another entity in the association. (Compare with: key agreement.)

      (O) "The procedure to send a symmetric key from one party to other
      parties. As a result, all legitimate participants share a common
      symmetric key in such a way that the symmetric key is determined
      entirely by one party." [A9042]

   $ key update
      (I) Derive a new key from an existing key. (See: certificate
      rekey.)

   $ key validation
      (N) "The procedure for the receiver of a public key to check that
      the key conforms to the arithmetic requirements for such a key in
      order to thwart certain types of attacks." [A9042]

   $ keyed hash
      (I) A cryptographic hash in which the mapping to a hash result is
      varied by a second input parameter that is a cryptographic key.
      (For example, see [R1828].) (See: checksum.)

      (C) If the input data set is changed, a new hash result cannot be
      correctly computed without knowledge of the secret key. Thus, the
      secret key protects the hash result so it can be used as a
      checksum even when there is a threat of an active attack on the
      data.

      (C) There are least two forms of keyed hash: (a) A function based
      on a keyed encryption algorithm. (For example, see: Data
      Authentication Code.) (b) A keyless hash that is enhanced by
      combining (for example, by concatenating) the input data set
      parameter with a key parameter before mapping to the hash result.

   $ keying material
      (I) Data (such as key pairs and initialization values) needed to
      establish and maintain a cryptographic security association.



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   $ KMID
      See: key material identifier.

   $ known-plaintext attack
      (I) A cryptanalysis approach in which the analyst tries to
      determine the key from knowledge of some plaintext-ciphertext
      pairs (although the analyst may also know other clues, such as the
      cryptographic algorithm).

   $ L2F
      See: Layer 2 Forwarding Protocol.

   $ L2TP
      See: Layer 2 Tunneling Protocol.

   $ Language of Temporal Ordering Specification (LOTOS)
      (N) A language (ISO 8807-1990) for formal specification of
      computer network protocols; describes the order in which events
      occur.

   $ label
      See: security label.

   $ lattice model
      (I) A security model for flow control in a system, based on the
      "lattice" that is formed by the finite security levels in a system
      and their partial ordering. [Denn] (See: flow control, security
      level, security model.)

   $ Law Enforcement Access Field (LEAF)
      (N) A data item that is automatically embedded in data encrypted
      by devices (e.g., see: CLIPPER chip) that implement the Escrowed
      Encryption Standard.

   $ Layer 2 Forwarding Protocol (L2F)
      (N) An Internet protocol (originally developed by Cisco
      Corporation) that uses tunneling of PPP over IP to create a
      virtual extension of a dial-up link across a network, initiated by
      the dial-up server and transparent to the dial-up user. (See:
      L2TP.)

   $ Layer 2 Tunneling Protocol (L2TP)
      (N) An Internet client-server protocol that combines aspects of
      PPTP and L2F and supports tunneling of PPP over an IP network or
      over frame relay or other switched network. (See: virtual private
      network.)

      (C) PPP can in turn encapsulate any OSI layer 3 protocol. Thus,
      L2TP does not specify security services; it depends on protocols
      layered above and below it to provide any needed security.




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   $ LDAP
      See: Lightweight Directory Access Protocol.

   $ least privilege
      (I) The principle that a security architecture should be designed
      so that each system entity is granted the minimum system resources
      and authorizations that the entity needs to do its work. (See:
      economy of mechanism.)

      (C) This principle tends to limit damage that can be caused by an
      accident, error, or unauthorized act.

   $ Lightweight Directory Access Protocol (LDAP)
      (N) A client-server protocol that supports basic use of the X.500
      Directory (or other directory servers) without incurring the
      resource requirements of the full Directory Access Protocol (DAP).
      [R1777]

      (C) Designed for simple management and browser applications that
      provide simple read/write interactive directory service. Supports
      both simple authentication and strong authentication of the client
      to the directory server.

   $ link
      (I) Subnetwork usage: A point-to-point communication channel
      connecting two computers, especially one between two subnetwork
      packet switches that is implemented at OSI layer 2. (See: link
      encryption.)

      (C) Switches assume that links are logically passive. If a switch
      at one end of a link sends a sequence of bits, the sequence simply
      arrives at the other end after a finite time, although some bits
      may have been changed either accidentally (errors) or by active
      wiretapping.

      (I) World Wide Web usage: See: hyperlink.

   $ link encryption
   $ link-by-link encryption
      (I) Stepwise protection of data that flows between two points in a
      network, provided by encrypting data separately on each network
      link--i.e., by encrypting data when it leaves a host or subnetwork
      switch and decrypting when it arrives at the next host or switch.
      Each link may use a different key or even a different algorithm.
      [R1455] (See: end-to-end encryption.)

   $ logic bomb
      (I) Malicious logic that activates when specified conditions are
      met and causes denial of service or damage to system resources.
      (See: Trojan horse, virus, worm.)




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   $ login
      (I) The act of a system entity gaining access to a session of
      using system resources; usually accomplished by providing a user
      name and password to an access control system that authenticates
      the user.

      (C) Derives from "log" file", a security audit trail that records
      security events, such as the beginning of sessions, and who
      initiates them.

   $ LOTOS
      See: Language of Temporal Ordering Specification.

   $ MAC
      See: mandatory access control, Message Authentication Code.

   $ malicious logic
      (I) Hardware, software, or firmware that is intentionally included
      or inserted in a system for a harmful purpose. (See: logic bomb,
      Trojan horse, virus, worm.)

   $ malware
      (I) A contraction of "malicious software". (See: malicious logic.)

      (D) ISPDs SHOULD NOT use this term because it is not listed in
      most dictionaries and could confuse international readers.

   $ man-in-the-middle
      (I) A form of active wiretapping attack in which the attacker
      intercepts and selectively modifies communicated data in order to
      masquerade as one or more of the entities involved in a
      communication association. (See: hijack attack, piggyback attack.)

      (C) For example, suppose Alice and Bob try to establish a session
      key by using the Diffie-Hellman algorithm without data origin
      authentication service. A "man in the middle" could block direct
      communication between Alice and Bob--and then masquerade as Alice
      sending data to Bob, masquerade as Bob sending data to Alice,
      establish separate session keys with each of them, and function as
      a clandestine proxy server between them in order to capture or
      modify sensitive information that Alice and Bob think they are
      sending only to each other.

   $ mandatory access control (MAC)
      (I) An access control service that enforces a security policy
      based on comparing (a) security labels that indicate how sensitive
      or critical system resources are with (b) security clearances that
      authorize system entities to access certain resources. (See:
      discretionary access control, rule-based security policy.)

      (C) This kind of access control is called "mandatory" because an
      entity that has clearance to access a resource may not, just by


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      its own volition, enable another entity to access that resource.

      (O) "A means of restricting access to objects based on the
      sensitivity (as represented by a label) of the information
      contained in the objects and the formal authorization (i.e.,
      clearance) of subjects to access information of such sensitivity."
      [DOD1]

   $ manipulation detection code
      (D) ISPDs SHOULD NOT use this term as a synonym for "checksum"
      because the word "manipulation" implies protection against active
      attacks, which an ordinary checksum might not provide. Instead, if
      such protection is intended, use "protected checksum" or some
      particular type thereof, depending on which is meant. If such
      protection is not intended, use "error detection code" or some
      specific type of checksum that is not protected.

   $ masquerade attack
      (I) A type of attack in which one system entity illegitimately
      poses as (assumes the identity of) another entity. (See: spoofing
      attack.)

   $ MCA
      See: merchant certificate authority.

   $ MD2
      (N) A cryptographic hash [R1319] that produces a 128-bit hash
      result, was designed by Ron Rivest, and is similar to MD4 and MD5
      but slower. (See: message digest.)

   $ MD4
      (N) A cryptographic hash [R1320] that produces a 128-bit hash
      result and was designed by Ron Rivest. (See: message digest and
      SHA-1.)

   $ MD5
      (N) A cryptographic hash [R1321] that produces a 128-bit hash
      result and was designed by Ron Rivest to be an improved version of
      MD4.

   $ merchant
      (O) SET usage: "A seller of goods, services, and/or other
      information who accepts payment for these items electronically."
      [SET2] A merchant may also provide electronic selling services
      and/or electronic delivery of items for sale. With SET, the
      merchant can offer its cardholders secure electronic interactions,
      but a merchant that accepts payment cards is required to have a
      relationship with an acquirer. [SET1, SET2]

   $ merchant certificate
      (O) SET usage: A public-key certificate issued to a merchant.
      Sometimes used to refer to a pair of such certificates where one


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      is for digital signature use and the other is for encryption.

   $ merchant certification authority (MCA)
      (O) SET usage: A CA that issues digital certificates to merchants
      and is operated on behalf of a payment card brand, an acquirer, or
      another party according to brand rules. Acquirers verify and
      approve requests for merchant certificates prior to issuance by
      the MCA. An MCA does not issue a CRL, but does distribute CRLs
      issued by root CAs, brand CAs, geopolitical CAs, and payment
      gateway CAs. [SET2]

   $ mesh PKI
      (I) A non-hierarchical PKI architecture in which there are several
      trusted CAs rather than a single root. Each certificate user bases
      path validations on the public key of one of the trusted CAs,
      usually the one that issued that user's own public-key
      certificate. Rather than having superior-to-subordinate
      relationships between CAs, the relationships are peer-to-peer, and
      CAs issue cross-certificates to each other. (See: hierarchical
      PKI, trust-file PKI.)

   $ message authentication code vs. Message Authentication Code (MAC)
      1. (N) Capitalized: "(The) Message Authentication Code" refers to
      an ANSI standard [A9009] for a checksum that is computed by a
      keyed hash that is based on DES. (Also known as the U.S.
      Government standard Data Authentication Code [FP113].)

      (C) The ANSI standard MAC algorithm is equivalent to cipher block
      chaining with IV = 0. MAC is also known as the U.S. Government
      standard Data Authentication Code [FP113].

      2. (D) Not capitalized: ISPDs SHOULD NOT use "message
      authentication code", because this term mixes concepts in a
      potentially misleading way. Instead, use "checksum", "error
      detection code", "hash", "keyed hash", "Message Authentication
      Code", or "protected checksum", depending on what is meant.

      (C) The uncapitalized form is often misleadingly used as a synonym
      for keyed hash. The word "message" is misleading because it
      implies that the mechanism is particularly suitable for or limited
      to electronic mail (see: Message Handling Systems). The word
      "authentication" is misleading because the mechanism primarily
      serves a data integrity function rather than an authentication
      function. The word "code" is misleading because it implies that
      either encoding or encryption is involved, or that the term refers
      to computer software.

   $ message digest
      (D) ISPDs SHOULD NOT use this term as a synonym for "hash result"
      because it unnecessarily duplicates the meaning of the other, more
      general term and mixes concepts in a potentially misleading way.
      (See: cryptographic hash, Message Handling System.)


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   $ Message Handling Systems `
      (I) A ITU-T/ISO system concept, which encompasses the notion of
      electronic mail but defines more comprehensive OSI systems and
      services that enable users to exchange messages on a store-and-
      forward basis. (The ISO equivalent is "Message Oriented Text
      Interchange System".) (See: X.400.)

   $ message indicator
      (D) ISPDs SHOULD NOT use this term as a synonym for
      "initialization value" because it mixes concepts in a potentially
      misleading way.

   $ message integrity check
   $ message integrity code
      (D) ISPDs SHOULD NOT use these terms because they mix concepts in
      a potentially misleading way. (The word "message" is misleading
      because it suggests that the mechanism is particularly suitable
      for or limited to electronic mail. The word "code" is misleading
      because it suggests that either encoding or encryption is
      involved, or that the term refers to computer software.) Instead,
      use "checksum", "error detection code", "hash", "keyed hash",
      "Message Authentication Code", or "protected checksum", depending
      on what is meant.

   $ Message Security Protocol (MSP)
      (N) A secure message handling protocol [SDNS7] for use with X.400
      and Internet mail protocols. Developed by NSA's SDNS program and
      used in the U.S. Defense Message System.

   $ MHS
      See: message handling system.

   $ MIME
      See: Multipurpose Internet Mail Extensions.

   $ MIME Object Security Services (MOSS)
      (I) An Internet protocol [R1848] that applies end-to-end
      encryption and digital signature to MIME message content, using
      symmetric cryptography for encryption and asymmetric cryptography
      for key distribution and signature. MOSS is based on features and
      specifications of PEM. (See: S/MIME.)

   $ Minimum Interoperability Specification for PKI Components (MISPC)
      (N) A technical description to provide a basis for interoperation
      between PKI components from different vendors; consists primarily
      of a profile of certificate and CRL extensions and a set of
      transactions for PKI operation. [MISPC]

   $ MISPC
      See: Minimum Interoperability Specification for PKI Components.



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   $ MISSI
      (N) Multilevel Information System Security Initiative, an NSA
      program to encourage development of interoperable, modular
      products for constructing secure network information systems in
      support of a wide variety of Government missions. (See: MSP.)

   $ MISSI user
      (O) MISSI usage: A system entity that is the subject of one or
      more MISSI X.509 public-key certificates issued under a MISSI
      certification hierarchy. (See: personality.)

      (C) MISSI users include both end users and the authorities that
      issue certificates. A MISSI user is usually a person but may be a
      machine or other automated process. Some machines are required to
      operate non-stop. To avoid downtime needed to exchange the
      FORTEZZA cards of machine operators at shift changes, the machines
      may be issued their own cards, as if they were persons.

   $ mode
   $ mode of operation
      (I) Encryption usage: A technique for enhancing the effect of a
      cryptographic algorithm or adapting the algorithm for an
      application, such as applying a block cipher to a sequence of data
      blocks or a data stream. (See: electronic codebook, cipher block
      chaining, cipher feedback, output feedback.)

      (I) System operation usage: A type of security policy that states
      the range of classification levels of information that a system is
      permitted to handle and the range of clearances and authorizations
      of users who are permitted to access the system. (See: dedicated
      security mode, multilevel security mode, partitioned security
      mode, system high security mode.)

   $ modulus
      (I) The defining constant in modular arithmetic, and usually a
      part of the public key in asymmetric cryptography that is based on
      modular arithmetic. (See: Diffie-Hellman, Rivest-Shamir-Adleman.)

   $ Morris Worm
      (I) A worm program written by Robert T. Morris, Jr. that flooded
      the ARPANET in November, 1988, causing problems for thousands of
      hosts. (See: worm.)

   $ MOSS
      See: MIME Object Security Services.

   $ MSP
      See: Message Security Protocol.

   $ multilevel secure (MLS)
      (I) A class of system that has system resources (particularly
      stored information) at more than one security level (i.e., has


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      different types of sensitive resources) and that permits
      concurrent access by users who differ in security clearance and
      need-to-know, but is able to prevent the users from accessing
      resources for which they lack authorization.

   $ multilevel security mode
      (I) A mode of operation of an information system, that allows two
      or more classification levels of information to be processed
      concurrently within the same system when not all users have a
      clearance or formal access authorization for all data handled by
      the AIS.

      (C) This mode is defined formally in U.S. Department of Defense
      policy regarding system accreditation [DOD2], but the term is also
      used outside the Defense Department and outside the Government.

   $ Multipurpose Internet Mail Extensions (MIME)
      (I) An Internet protocol [R2045] that enhances the basic format of
      Internet electronic mail messages [R0822] to be able to use
      character sets other than US-ASCII for textual headers and text
      content, and to carry non-textual and multi-part content. (See:
      S/MIME.)

   $ mutual suspicion
      (I) The state that exists between two interacting system entities
      in which neither entity can trust the other to function correction
      with regard to some security requirement.

   $ National Computer Security Center (NCSC)
      (N) A U.S. Department of Defense organization, housed in NSA, that
      has responsibility for encouraging widespread availability of
      trusted computer systems throughout the Federal Government. It has
      established criteria for, and performs evaluations of, computer
      and network systems that have a trusted computing base. (See:
      Evaluated Products List, Rainbow Series, TCSEC.)

   $ National Information Assurance Partnership (NIAP)
      (N) An organization created by NIST and NSA to enhance the quality
      of commercial products for information security and increase
      consumer confidence in those products through objective evaluation
      and testing methods.

      (C) NIAP is registered, through the U.S. Department of Defense, as
      a National Performance Review Reinvention Laboratory. NIAP
      functions include the following:

       - Developing tests, test methods, and other tools that developers
         and testing laboratories may use to improve and evaluate
         security products.
       - Collaborating with industry and others on research and testing
         programs.
       - Using the Common Criteria to develop protection profiles and


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         associated test sets for security products and systems.
       - Cooperating with the NIST National Voluntary Laboratory
         Accreditation Program to develop a program to accredit private-
         sector laboratories for the testing of information security
         products using the Common Criteria.
       - Working to establish a formal, international mutual recognition
         scheme for a Common Criteria-based evaluation.

   $ National Institute of Standards and Technology (NIST)
      (N) A U.S. Department of Commerce agency that promotes U.S.
      economic growth by working with industry to develop and apply
      technology, measurements, and standards. Has primary Government
      responsibility for INFOSEC standards for unclassified but
      sensitive information. (See: ANSI, DES, DSA, DSS, FIPS, NIAP,
      NSA.)

   $ National Security Agency (NSA)
      (N) A U.S. Department of Defense intelligence agency that has
      primary Government responsibility for INFOSEC for classified
      information and for unclassified but sensitive information handled
      by national security systems. (See: FORTEZZA, KEA, MISSI, NIAP,
      NIST, SKIPJACK.)

   $ need-to-know
      (I) The necessity for access to, knowledge of, or possession of
      specific information required to carry out official duties.

      (C) This criterion is used in security procedures that require a
      custodian of sensitive information, prior to disclosing the
      information to someone else, to establish that the intended
      recipient has proper authorization to access the information.

   $ network
      See: computer network.

   $ NIAP
      See: National Information Assurance Partnership.

   $ NIST
      See: National Institute of Standards and Technology.

   $ NLSP
      Network Layer Security Protocol. An OSI protocol (IS0 11577) for
      end-to-end encryption services at the top of OSI layer 3. NLSP is
      derived from an SDNS protocol, SP3, but is much more complex.

   $ no-lone zone
      (I) A room or other space to which no person may have
      unaccompanied access and that, when occupied, is required to be
      occupied by two or more appropriately authorized persons. (See:
      dual control.)



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   $ nonce
      (I) A random or non-repeating value that is included in data
      exchanged by a protocol, usually for the purpose of guaranteeing
      liveness and thus detecting and protecting against replay attacks.

   $ non-critical
      See: critical (extension of certificate).

   $ non-repudiation service
      (I) A security service that provide protection against false
      denial of involvement in a communication. (See: repudiation.)

      (C) Non-repudiation service does not and cannot prevent an entity
      from repudiating a communication. Instead, the service provides
      evidence that can be stored and later presented to a third party
      to resolve disputes that arise if and when a communication is
      repudiated by one of the entities involved. There are two basic
      kinds of non-repudiation service:

       - "Non-repudiation with proof of origin" provides the recipient
         of data with evidence that proves the origin of the data, and
         thus protects the recipient against an attempt by the
         originator to falsely deny sending the data. This service can
         be viewed as a stronger version of an data origin
         authentication service, in that it proves authenticity to a
         third party.

       - "Non-repudiation with proof of receipt" provides the originator
         of data with evidence that proves the data was received as
         addressed, and thus protects the originator against an attempt
         by the recipient to falsely deny receiving the data.

      (C) Phases of a Non-Repudiation Service: Ford [For94, For97] uses
      the term "critical action" to refer to the act of communication
      that is the subject of the service:

      --------   --------   --------   --------   --------   . --------
      Phase 1:   Phase 2:   Phase 3:   Phase 4:   Phase 5:   . Phase 6:
      Request    Generate   Transfer   Verify     Retain     . Resolve
      Service    Evidence   Evidence   Evidence   Evidence   . Dispute
      --------   --------   --------   --------   --------   . --------

      Service    Critical   Evidence   Evidence   Archive    . Evidence
      Request => Action  => Stored =>  Is      => Evidence   . Is
      Is Made    Occurs     For Later  Tested     In Case    . Verified
                 and        Use |          ^      Critical   .     ^
                 Evidence       v          |      Action Is  .     |
                 Is         +-------------------+ Repudiated .     |
                 Generated  |Verifiable Evidence|------> ... . ----+
                            +-------------------+

      1. Before the critical action, the service requester asks, either


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         implicitly or explicitly, to have evidence of the action be
         generated.
      2. When the critical action occurs, evidence is generated by a
         process involving the potential repudiator and possibly also a
         trusted third party.
      3. The evidence is transferred to the requester, or stored by a
         third party, for later use if needed.
      4. The entity that holds the evidence tests to be sure that it
         will suffice if a dispute arises.
      5. The evidence is retained for possible future retrieval and use.

      6. In this phase, which occurs only if the critical action is
         repudiated, the evidence is retrieved from storage, presented,
         and verified to resolve the dispute.

   $ no-PIN ORA (NORA)
      (O) MISSI usage: An organizational RA that operates in a mode in
      which the ORA performs no card management functions and,
      therefore, does not require knowledge of either the SSO PIN or
      user PIN for an end user's FORTEZZA PC card.

   $ NORA
      See: no-PIN ORA.

   $ notarization
      (I) Registration of data under the authority or in the care of a
      trusted third party, thus making it possible to provide subsequent
      assurance of the accuracy of characteristics claimed for the data,
      such as content, origin, time, and delivery. [I7498 Part 2] (See:
      digital notary.)

   $ NULL encryption algorithm
      (I) An algorithm [R2410] that does nothing to alter plaintext
      data. It originated because of IPsec ESP, which always specifies
      the use of an encryption algorithm to provide confidentiality. The
      NULL encryption algorithm is a convenient way to represent the
      option of not applying encryption in ESP (or in any other context
      where this is needed).

   $ OAKLEY
      (I) An key establishment protocol [R2412] (proposed for IPsec but
      superseded by IPsec Key Exchange) that is based on the Diffie-
      Hellman algorithm and designed to be a compatible component of
      ISAKMP. In addition to securely sharing a secret key between two
      entities, OAKLEY provides authentication service to ensure the
      entities of each other's identity, even if the exchange is
      attacked by active wiretapping.

      (C) Establishes a shared key with an assigned identifier and
      associated authenticated identities for two parties. Each key is
      associated with algorithms used for authentication,
      confidentiality, and one-way functions. Related to STS, sharing


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      the similarity of authenticating the Diffie-Hellman exponentials
      and using them for determining a shared session key, and also of
      achieving public-key forward secrecy for the shared key. Supports
      key updates, incorporation of keys distributed by out-of-band
      mechanisms, and user-defined abstract group structures for use
      with Diffie-Hellman.

   $ object
      (I) Trusted computer system modeling usage: A system element that
      contains or receives information. (See: Bell-LaPadula Model,
      trusted computer system.)

   $ object identifier (OID)
      (I) An official, globally unique name for a thing, written as a
      sequence of integers formed and assigned as defined in the ASN.1
      standard and used to reference the thing in abstract
      specifications and during the negotiation of security services in
      a protocol.

      (O) "A value (distinguishable from all other such values) which is
      associated with an object." [X680]

      (C) Objects named by OIDs are leaves of the object identifier tree
      (which is similar to but different from the X.500 Directory
      Information Tree). Each arc (i.e., each branch of the tree) is
      labeled with a non-negative integer. An OID is the sequence of
      integers on the path leading from the root of the tree to a named
      object.

      (C) The OID tree has three arcs immediately below the root: {0}
      for use by ITU-T, {1} for use by ISO, and {2} for use by both
      jointly. Below ITU-T are four arcs, where {0 0} is for ITU-T
      recommendations. Below {0 0} are 26 arcs, one for each series of
      recommendations starting with the letters A to Z, and below these
      are arcs for each recommendation. Thus, the OID for ITU-T
      Recommendation X.509 is {0 0 24 509}. Below ISO are four arcs,
      where {1 0 }is for ISO standards, and below these are arcs for
      each ISO standard. Thus, the OID for ISO/IEC 9594-8 (the ISO
      number for X.509) is {1 0 9594 8}.

      (C) The following are additional examples: ANSI registers
      organization names below the branch {joint-iso-ccitt(2)
      country(16) US(840) organization(1)}. The NIST CSOR records PKI
      objects below the branch {joint-iso-ccitt(2) country(16) us(840)
      gov(101) csor(3) pki(4)}. The U.S. Department of Defense registers
      INFOSEC objects below the branch {joint-iso-ccitt(2) country(16)
      us(840) organization(1) gov(101) dod(2) infosec(1)}. The OID for
      the PKIX private extension is defined in an arc below the arc for
      the PKIX name space, as {iso(1) identified-organization(3) dod(6)
      internet(1) security(5) mechanisms(5) pkix(7) 1 1}.




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   $ object reuse
      (N) "The reassignment and reuse of a storage medium (e.g., page
      frame, disk sector, magnetic tape) that once contained one or more
      [information] objects. To be securely reused and assigned to a new
      subject, storage media must contain no residual data (magnetic
      remanence) from the object(s) previously contained in the media."
      [NCS04]

   $ OCSP
      See: On-line Certificate Status Protocol.

   $ octet
      (I) A data unit of eight bits. (See: byte.)

      (c) This term is used in networking (especially in OSI standards)
      in preference to "byte", because some systems use "byte" for data
      storage units of a size other than eight.

   $ OFB
      See: output feedback.

   ohnosecond
      (C) That minuscule fraction of time in which you realize that your
      private key has been compromised.

   $ OID
      See: object identifier.

   $ On-line Certificate Status Protocol (OCSP)
      (I) An Internet protocol used by a client to obtain from a server
      the validity status and other information concerning a digital
      certificate.

      (C) In some applications, such as those involving high-value
      commercial transactions, it may be necessary to obtain certificate
      revocation status that is more timely than is possible with CRLs
      or to obtain other kinds of status information. OCSP may be used
      to determine the current revocation status of a digital
      certificate, in lieu of or as a supplement to checking against a
      periodic CRL. An OCSP client issues a status request to an OCSP
      server and suspends acceptance of the certificate in question
      until the server provides a response.

   $ one-time pad
      (I) An encryption algorithm in which the key is a random sequence
      of symbols and each symbol is used for encryption only one time--
      to encrypt only one plaintext symbol to produce only one
      ciphertext symbol--and a copy of the key is used similarly for
      decryption.

      (C) To ensure one-time use, the copy of the key used for
      encryption is destroyed after use, as is the copy used for


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      decryption. This is the only encryption algorithm that is truly
      unbreakable, even given unlimited resources for cryptanalysis
      [Schn], but key management costs and synchronization problems make
      it impractical except in special situations.

   $ one-time password
   $ One-Time Password (OTP)
      1. Not capitalized: A "one-time password" is a simple
      authentication technique in which each password is used only once
      as authentication information that verifies an identity. This
      technique counters the threat of a replay attack that uses
      passwords captured by wiretapping.

      2. Capitalized: "One-Time Password" is an Internet protocol that
      is based on S/KEY and uses a cryptographic hash function to
      generate one-time passwords for use as authentication information
      in system login and other processes that need protection against
      replay attacks. [R1938]

   $ one-way encryption
      (I) Irreversible transformation of plaintext to ciphertext, such
      that the plaintext cannot be recovered from the ciphertext by
      other than exhaustive procedures even if the cryptographic key is
      known. (See: encryption.)

   $ one-way function
      (I) "A (mathematical) function, f, which is easy to compute, but
      which for a general value y in the range, it is computationally
      difficult to find a value x in the domain such that f(x) = y.
      There may be a few values of y for which finding x is not
      computationally difficult." [X509]

      (D) ISPDs SHOULD NOT use this term as a synonym for "cryptographic
      hash".

   $ open security environment
      (O) DoD usage: A system environment that meets at least one of the
      following conditions: (a) Application developers (including
      maintainers) do not have sufficient clearance or authorization to
      provide an acceptable presumption that they have not introduced
      malicious logic. (b) Configuration control does not provide
      sufficient assurance that applications and the equipment are
      protected against the introduction of malicious logic prior to and
      during the operation of system applications. [NCS04] (See: closed
      security environment.)

   $ Open Systems Interconnection (OSI) Reference Model (OSIRM)
      (N) A joint ISO/ITU-T standard [I7498 Part 1] for a seven-layer,
      architectural communication framework for interconnection of
      computers in networks.

      (C) OSI-based standards include communication protocols that are


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      mostly incompatible with the Internet Protocol Suite, but also
      include security models, such as X.509, that are used in the
      Internet.

      (C) The OSIRM layers, from highest to lowest, are (7) Application,
      (6) Presentation, (5) Session, (4) Transport, (3) Network, (2)
      Data Link, and (1) Physical. In this Glossary, these layers are
      referred to by number to avoid confusing them with Internet
      Protocol Suite layers, which are referred to by name.

      (C) Some unknown person described how the OSI layers correspond to
      the seven deadly sins:

      7. Wrath: Application is always angry at the mess it sees below
         itself. (Hey! Who is it to be pointing fingers?)
      6. Sloth: Presentation is too lazy to do anything productive by
         itself.
      5. Lust: Session is always craving and demanding what truly
         belongs to Application's functionality.
      4. Avarice: Transport wants all of the end-to-end functionality.
         (Of course, it deserves it, but life isn't fair.)
      3. Gluttony: (Connection-Oriented) Network is overweight and
         overbearing after trying too often to eat Transport's lunch.
      2. Envy: Poor Data Link is always starved for attention. (With
         ATM, maybe now it is feeling less neglected.)
      1. Pride: Physical has managed to avoid much of the controversy,
         and nearly all of the embarrassment, suffered by the others.

      (C) John G. Fletcher described how the OSI layers also correspond
      to Snow White's dwarf friends:

      7. Doc: Application acts as if it is in charge, but sometimes
         muddles its syntax.
      6. Sleepy: Presentation is indolent, being guilty of the sin of
         Sloth.
      5. Dopey: Session is confused because its charter is not very
         clear.
      4. Grumpy: Transport is irritated because Network has encroached
         on Transport's turf.
      3. Happy: Network smiles for the same reason that Transport is
         irritated.
      2. Sneezy: Data Link makes loud noises in the hope of attracting
         attention.
      1. Bashful: Physical quietly does its work, unnoticed by the
         others.

   $ operational integrity
      (I) A synonym for "system integrity"; emphasizes the actual
      performance of system functions rather than just the ability to
      perform them.




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   $ operations security (OPSEC)
      (I) A process to identify, control, and protect evidence of the
      planning and execution of sensitive activities and operations, and
      thereby prevent potential adversaries from gaining knowledge of
      capabilities and intentions.

   $ OPSEC
      See: operations security.

   $ ORA
      See: organizational registration authority.

   $ Orange Book
      (D) ISPDs SHOULD NOT use this term as a synonym for "Trusted
      Computer System Evaluation Criteria" [CSC001, DOD1]. Instead, use
      the full, proper name of the document or, in subsequent
      references, the conventional abbreviation "TCSEC". (See: (usage
      note under) Green Book.)

   $ organizational certificate
      (O) MISSI usage: A type of MISSI X.509 public-key certificate that
      is issued to support organizational message handling for the U.S.
      Government's Defense Message System.

   $ organizational registration authority (ORA)
      (I) General usage: An RA for an organization.

      (O) MISSI usage: The MISSI implementation of RA. A MISSI end
      entity that assists a PCA, CA, or SCA to register other end
      entities, by gathering, verifying, and entering data and
      forwarding it to the signing authority, and may also assist with
      card management functions. An ORA is a local administrative
      authority, and the term refers both to the office or role, and to
      the person who fills that office. An ORA does not sign
      certificates, CRLs, or CKLs. (See: no-PIN ORA, SSO-PIN ORA, user-
      PIN ORA.)

   $ origin authentication
   $ origin authenticity
      (D) ISPDs SHOULD NOT use these terms because they look like
      careless use of an internationally standardized term. Instead, use
      "data origin authentication" or "data origin authentication
      service".

   $ OSI
   $ OSIRM
      See: Open Systems Interconnection Reference Model.

   $ OTP
      See: One-Time Password.




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   $ out of band
      (I) Transfer of information using a channel that is outside (i.e.,
      separate from) the channel that is normally used. (See: covert
      channel.)

      (C) Out-of-band mechanisms are often used to distribute shared
      secrets (e.g., a symmetric key) or other sensitive information
      items (e.g., a root key) that are needed to initialize or
      otherwise enable the operation of cryptography or other security
      mechanisms. (See: key distribution.)

   $ output feedback (OFB)
      (N) A block cipher mode [FP081] that modifies electronic codebook
      mode to operate on plaintext segments of variable length less than
      or equal to the block length.

      (C) This mode operates by directly using the algorithm's
      previously generated output block as the algorithm's next input
      block (i.e., by "feeding back" the output block) and combining
      (exclusive OR-ing) the output block with the next plaintext
      segment (of block length or less) to form the next ciphertext
      segment.

   $ outside attack
   $ outsider attack
      See: (secondary definition in) attack.

   $ P1363
      See: IEEE P1363.

   $ PAA
      See: policy approving authority.

   $ packet filter
      See: (secondary definition in) filtering router.

   $ pagejacking
      (I) A contraction (of Web PAGE hiJACKING); a masquerade attack in
      which the attacker copies (steals) a home page or other material
      from the target server, rehosts the page on a server the attacker
      controls, and causes the rehosted page to be indexed by the major
      Web search services, thereby diverting browsers from the target
      server to the attacker's server.

      (D) ISPDs SHOULD NOT use this term because it is not listed in
      most dictionaries and might confuse international readers.

   $ PAN
      See: primary account number.

   $ PAP
      See: Password Authentication Protocol.


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   $ partitioned security mode
      (N) A mode of operation of an information system, wherein all
      users have the clearance, but not necessarily formal access
      authorization and need-to-know, for all information handled by the
      system. (This mode is defined formally in U.S. Department of
      Defense policy regarding system accreditation [DOD2].)

   $ passive attack
      See: (secondary definition in) attack.

   $ passive wiretapping
      See: (secondary definition in) wiretapping.

   $ password
      (I) A secret data value, usually a character string, that is used
      as authentication information. (See: challenge-response.)

      (C) A password is usually matched with a user identifier that is
      explicitly presented in the authentication process, but in some
      cases the identity may be implicit.

      (C) Using a password as authentication information assumes that
      the password is known only by the system entity whose identity is
      being authenticated. Therefore, in a network environment where
      wiretapping is possible, simple authentication that relies on
      transmission of static (repetitively used) passwords as cleartext
      is inadequate. (See: one-time password, strong authentication.)

   $ Password Authentication Protocol (PAP)
      (I) A simple authentication mechanism in PPP, in which a user
      identifier and password are transmitted in cleartext. [R1334]
      (See: CHAP.)

   $ password sniffing
      (I) Passive wiretapping, usually on local area network, to gain
      knowledge of passwords. (See: (usage note in) sniffing.)

   $ path discovery
      (I) For a given digital certificate, the process of finding a set
      of public-key certificates that comprise a certification path from
      a trusted key to that digital certificate.

   $ path validation
      (I) The process of validating all of the digital certificates in a
      certification path and the required relationships between those
      certificates, thus validating the contents of the last certificate
      on the path. (See: certificate validation.)

   $ payment card
      (N) SET usage: Collectively refers "to credit cards, debit cards,
      charge cards, and bank cards issued by a financial institution and


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      which reflects a relationship between the cardholder and the
      financial institution." [SET2]

   $ payment gateway
      (O) SET usage: A system operated by an acquirer, or a third party
      designated by an acquirer, for the purpose of providing electronic
      commerce services to the merchants in support of the acquirer, and
      which interfaces to the acquirer to support the authorization,
      capture, and processing of merchant payment messages, including
      payment instructions from cardholders. [SET1, SET2]

   $ payment gateway certification authority (SET PCA)
      (O) SET usage: A CA that issues digital certificates to payment
      gateways and is operated on behalf of a payment card brand, an
      acquirer, or another party according to brand rules. A SET PCA
      issues a CRL for compromised payment gateway certificates. [SET2]
      (See: PCA.)

   $ PC card
      (N) A plug-in peripheral device, originally developed for portable
      computers, that provides for functional expansion--such as
      removable storage, modems, device interface adapters, and
      cryptographic modules--in an internationally standardized, non-
      proprietary form factor about the size of a credit card. (See:
      FORTEZZA, PCMCIA.)

      (C) The PC Card Standard defines a 68-pin interface between the
      peripheral and the socket and defines three standard sizes, Types
      I, II and III. All three have the same length and width, roughly
      the size of a credit card, but differ in their thickness from 3.3
      to 10.5 mm.

   $ PCA
      (D) ISPDs SHOULD NOT use this acronym without a qualifying
      adjective because that would be ambiguous. (See: Internet policy
      certification authority, (MISSI) policy creation authority, (SET)
      payment gateway certification authority.)

   $ PCMCIA
      (N) Personal Computer Memory Card International Association, an
      international group of manufacturers, developers, and vendors,
      founded in 1989 to standardize plug-in peripheral memory cards for
      personal computers and now extended to deal with any technology
      that works in the PC Card form factor.

   $ peer entity authentication
      (I) "The corroboration that a peer entity in an association is the
      one claimed." [I7498 Part 2] (See: authentication.)

   $ peer entity authentication service
      (I) A security service that verifies an identity claimed by or for
      a system entity in an association. (See: authentication,


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      authentication service.)

      (C) This service is used at the establishment of, or at times
      during, an association to confirm the identity of one entity to
      another, thus protecting against a masquerade by the first entity.
      However, unlike data origin authentication service, this service
      requires an association to exist between the two entities, and the
      corroboration provided by the service is valid only at the current
      time that the service is provided.

      (C) See: "relationship between data integrity service and
      authentication services" under data integrity service.

   $ PEM
      See: Privacy Enhanced Mail.

   $ penetration
      (I) Successful, repeatable, unauthorized access to a protected
      system resource. (See: attack, violation.)

   $ penetration test
      (I) A system test, often part of system certification, in which
      evaluators attempt to circumvent the security features of the
      system. [NCS04]

      (C) Penetration testing may be performed under various constraints
      and conditions. However, for a TCSEC evaluation, testers are
      assumed to have all system design and implementation
      documentation, including source code, manuals, and circuit
      diagrams, and to work under no greater constraints than those
      applied to ordinary users.

   $ perfect forward secrecy
      See: (discussion under) public-key forward secrecy.

   $ perimeter
      See: security perimeter.

   $ periods processing
      (I) A mode of system operation in which information of different
      sensitivities is processed at distinctly different times by the
      same system, with the system being properly purged or sanitized
      between periods. (See: color change.)

   $ permission
      (I) A synonym for "authorization", but "authorization" is
      preferred in the PKI context.

   $ personal identification number (PIN)
      (I) A character string used as a password to gain access to a
      system resource. (See: authentication information.)



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      (C) Despite the words "identification" and "number", a PIN seldom
      serves as a user identifier, and a PIN's characters are not
      necessarily all numeric. A better name for this concept would have
      been "personal authentication system string (PASS)".

      (C) Retail banking applications commonly use 4-character PINs.
      FORTEZZA PC card's use up to 12 characters for user or SSO PINs.

   $ personality
   $ personality label
      (O) MISSI usage: A set of MISSI X.509 public-key certificates that
      have the same subject DN, together with their associated private
      keys and usage specifications, that is stored on a FORTEZZA PC
      card to support a role played by the card's user.

      (C) When a card's user selects a personality to use in a FORTEZZA-
      aware application, the data determines behavior traits (the
      personality) of the application. A card's user may have multiple
      personalities on the card. Each has a personality label, a user-
      friendly character string that applications can display to the
      user for selecting or changing the personality to be used. For
      example, a military user's card might contain three personalities:
      GENERAL HALFTRACK, COMMANDER FORT SWAMPY, and NEW YEAR'S EVE BALL
      CHAIRMAN. Each personality includes one or more certificates of
      different types (such as DSA versus RSA), for different purposes
      (such as digital signature versus encryption), or with different
      authorizations.

   $ personnel security
      (I) Procedures to ensure that persons who access a system have
      proper authorization, clearance, and need-to-know as required by
      the system's security policy.

   $ PGP(trademark)
      See: Pretty Good Privacy.

   $ Photuris
      (I) A UDP-based, key establishment protocol for session keys,
      designed for use with the IPsec protocols AH and ESP. Superseded
      by IKE.

   $ phreak
   $ phreaking
      (I) A contraction (of "telePHone bREAKing"); penetration of a
      telephone system or, by extension, of any other communication or
      information system [Raym].

      (D) ISPDs SHOULD NOT use this term because it is not listed in
      most dictionaries and might confuse international readers.

   $ physical security
      (I) Fences, walls, locks, vaults, human guards and guard dogs,


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      sensors and alarms, and other tangible means of preventing
      unauthorized physical access to a system. [FP031, R1455]

   $ piggyback attack
      (I) A form of active wiretapping in which the attacker gains
      access to a system via intervals of inactivity in another user's
      legitimate communication connection. Sometimes called a "between-
      the-lines" attack. (See: hijack attack, man-in-the-middle attack.)

   $ PIN
      See: personal identification number.

   $ ping of death
      (I) An attack that sends an improperly large ICMP [R0792] echo
      request packet (a "ping") with the intent of overflowing the input
      buffers of the destination machine and causing it to crash.

   $ ping sweep
      (I) An attack that sends ICMP [R0792] echo requests ("pings") to
      range of IP addresses, with the goal of finding hosts that can be
      probed for vulnerabilities.

   $ PKCS
      See: Public-Key Cryptography Standards.

   $ PKCS #7
      (N) A standard [PKC07, R2315] from the PKCS series; defines a
      syntax for data that may have cryptography applied to it, such as
      for digital signatures and digital envelopes.

   $ PKCS #10
      (N) A standard [PKC10] from the PKCS series; defines a syntax for
      requests for public-key certificates. (See: certification
      request.)

      (C) A PKCS #10 request contains a DN and a public key, and may
      contain other attributes, and is signed by the entity making the
      request. The request is sent to a CA, who converts it to an X.509
      public-key certificate (or some other form), and returns it,
      possibly in PKCS #7 format.

   $ PKCS #11
      (N) A standard [PKC11] from the PKCS series; defines a software
      CAPI called Cryptoki (pronounced "crypto-key"; short for
      "cryptographic token interface") for devices that hold
      cryptographic information and perform cryptographic functions.

   $ PKI
      See: public-key infrastructure.

   $ PKIX
      (I) (1.) A contraction of "Public-Key Infrastructure (X.509)", the


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      name of the IETF working group that is specifying an architecture
      and set of protocols needed to support an X.509-based PKI for the
      Internet. (2.) A collective name for that architecture and set of
      protocols.

      (C) The goal of PKIX is to facilitate the use of X.509 public-key
      certificates in multiple Internet applications and to promote
      interoperability between different implementations that use those
      certificates. The resulting PKI is intended to provide a framework
      that supports a range of trust and hierarchy environments and a
      range of usage environments. PKIX specifies (a) profiles of the v3
      X.509 public-key certificate standards and the v2 X.509 CRL
      standards for the Internet, (b) operational protocols used by
      relying parties to obtain information such as certificates or
      certificate status; (c) management protocols used by system
      entities to exchange information needed for proper management of
      the PKI; and (d) information about certificate policies and CPSs,
      covering the areas of PKI security not directly addressed in the
      rest of PKIX.

   $ PKIX private extension
      (I) PKIX defines a private extension to identify an on-line
      verification service supporting the issuing CA.

   $ plaintext
      (I) Data that is input to and transformed by an encryption
      process, or that is output by a decryption process.

      (C) Usually, the plaintext input to an encryption operation is
      cleartext. But in some cases, the input is ciphertext that was
      output from another encryption operation. (See: superencryption.)

   $ Point-to-Point Protocol (PPP)
      (I) An Internet protocol [R1661] for encapsulation and full-duplex
      transportation of network layer protocol (mainly OSI layer 3) data
      packets over a link between two peers, and for multiplexing
      different network layer protocols over the same link. Includes
      optional negotiation to select and use a peer entity
      authentication protocol to authenticate the peer to each other
      before they exchange network layer data. (See: CHAP, EAP, PAP.)

   $ Point-to-Point Tunneling Protocol (PPTP)
      (I) An Internet client-server protocol (originally developed by
      Ascend and Microsoft) that enables a dial-up user to create a
      virtual extension of the dial-up link across a network by
      tunneling PPP over IP. (See: L2TP.)

      (C) PPP can in turn encapsulate any or IPS network layer protocol
      (or OSI layer 3 protocol). Therefore, PPTP does not specify
      security services; it depends on protocols above and below it to
      provide any needed security. PPTP makes it possible to divorce the
      location of the initial dial-up server (the PPTP Access


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      Concentrator, the client, which runs on a special-purpose host)
      from the location at which the dial-up protocol (PPP) connection
      is terminated and access to the network is provided (the PPTP
      Network Server, which runs on a general-purpose host).

   $ policy
      (D) ISPDs SHOULD NOT this word as an abbreviation for either
      "security policy", "certificate policy", or other kinds of policy.
      Instead, to avoid misunderstanding, use the fully qualified term,
      at least at the point of first usage.

   $ policy approving authority (PAA)
      (O) MISSI usage: The top-level signing authority of a MISSI
      certification hierarchy. The term refers both that authoritative
      office or role, and to the person who fills that office. (See:
      root registry.)

      (C) A PAA registers MISSI PCAs and signs their X.509 public-key
      certificates. A PAA issues CRLs but does not issue a CKL. A PAA
      may issue cross-certificates to other PAAs.

   $ policy certification authority (Internet PCA)
      (I) An X.509-compliant CA at the second level of the Internet
      certification hierarchy, under the Internet Policy Registration
      Authority (IPRA). Each PCA operates in accordance with its
      published security policy (see: certification practice statement)
      and within constraints established by the IPRA for all PCAs.
      [R1422]. (See: policy creation authority.)

   $ policy creation authority (MISSI PCA)
      (O) MISSI usage: The second level of a MISSI certification
      hierarchy; the administrative root of a security policy domain of
      MISSI users and other, subsidiary authorities. The term refers
      both that authoritative office or role, and to the person who
      fills that office. (See: policy certification authority.)

      (C) A MISSI PCA's certificate is issued by a policy approving
      authority. The PCA registers the CAs in its domain, defines their
      configurations, and issues their X.509 public-key certificates.
      (The PCA may also issue certificates for SCAs, ORAs, and other end
      entities, but a PCA does not usually do this.) The PCA
      periodically issues CRLs and CKLs for its domain.

   $ Policy Management Authority
      (N) Canadian usage: An organization responsible for the oversight
      and policy management of the Government of Canada.

   $ policy mapping
      (I) "Recognizing that, when a CA in one domain certifies a CA in
      another domain, a particular certificate policy in the second
      domain may be considered by the authority of the first domain to
      be equivalent (but not necessarily identical in all respects) to a


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      particular certificate policy in the first domain." [X509]

   $ POP3
      See: Post Office Protocol, version 3.

   $ POP3 APOP
      (I) A "command" (better described as a transaction type, or a
      protocol-within-a-protocol) in POP3 [R1939], by which a POP3
      client optionally uses a keyed hash (based on MD5) to authenticate
      itself to a POP3 server and, depending on the server
      implementation, also to protect against replay attacks. (See:
      CRAM, POP3 AUTH, IMAP4 AUTHENTICATE.)

      (C) The server includes a unique timestamp in its greeting to the
      client. The subsequent APOP command sent by the client to the
      server contains the client's name and the hash result of applying
      MD5 to a string formed from the timestamp and a shared secret that
      is known only to the client and the server. APOP was designed as
      an alternative to using POP3's USER and PASS (i.e., password)
      command pair, in which the client sends a cleartext password to
      the server.

   $ POP3 AUTH
      (I) A "command" [R1734] (better described as a transaction type,
      or a protocol-within-a-protocol) in POP3, by which a POP3 client
      optionally proposes a mechanism to a POP3 server to authenticate
      the client to the server and provide other security services.
      (See: POP3 APOP, IMAP4 AUTHENTICATE.)

      (C) If the server accepts the proposal, the command is followed by
      performing a challenge-response authentication protocol and,
      optionally, negotiating a protection mechanism for subsequent POP3
      interactions. The security mechanisms used by POP3 AUTH are those
      used by IMAP4.

   $ port scan
      (I) An attack that sends client requests to a range of server port
      addresses on a host, with the goal of finding an active port and
      exploiting a known vulnerability of that service.

   $ POSIX
      (N) Portable Operating System Interface for Computer Environments,
      a standard [FP151, IS9945-1] (originally IEEE Standard P1003.1)
      that defines an operating system interface and environment to
      support application portability at the source code level. It is
      intended to be used by both application developers and system
      implementers.

      (C) P1003.1 supports security functionality like those on most
      UNIX systems, including discretionary access control and
      privilege. IEEE Draft Standard P1003.6.1 specifies additional
      functionality not provided in the base standard, including (a)


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      discretionary access control, (b) audit trail mechanisms, (c)
      privilege mechanisms, (d) mandatory access control, and (e)
      information label mechanisms.

   $ Post Office Protocol, version 3 (POP3)
      (I) An Internet protocol [R1939] by which a client workstation can
      dynamically access a mailbox on a server host to retrieve mail
      messages that the server has received and is holding for the
      client. (See: IMAP4.)

      (C) POP3 has mechanisms for optionally authenticating a client to
      a server and providing other security services. (See: POP3 APOP,
      POP3 AUTH.)

   $ PPP
      See: Point-to-Point Protocol.

   $ PPTP
      See: Point-to-Point Tunneling Protocol.

   $ pre-authorization
      (I) A capability of a CA that enable certification requests to be
      automatically validated against data provided in advance to the CA
      by an authorizing entity.

   $ Pretty Good Privacy(trademark) (PGP(trademark))
      (O) Trademarks of Network Associates, Inc., referring to a
      computer program and related protocols, that use cryptography to
      provide data security for electronic mail and other applications
      on the Internet. (See: MOSS, PEM, S/MIME.)

      (C) PGP encrypts messages with IDEA in CFB mode, distributes the
      IDEA keys by encrypting them with RSA, and creates digital
      signatures on messages with MD5 and RSA. To establish ownership of
      public keys, PGP depends on the web of trust. (Compare with:
      Privacy Enhanced Mail.)

   $ primary account number (PAN)
      (O) SET usage: "The assigned number that identifies the card
      issuer and cardholder. This account number is composed of an
      issuer identification number (see: bank identification number), an
      individual account number identification, and an accompanying
      check digit as defined by ISO 7812-1985." [SET2, IS7812]

      (C) The PAN is embossed, encoded, or both on a magnetic-strip-
      based credit card. The PAN identifies the issuer to which a
      transaction is to be routed and the account to which it is to be
      applied unless specific instructions indicate otherwise. The
      authority that assigns the bank identification number part of the
      PAN is the American Bankers Association.




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   $ privacy
      (I) The right of an entity (normally a person), acting in its own
      behalf, to determine the degree to which it will interact with its
      environment, including the degree to which the entity is willing
      to share information about itself with others. (See: anonymity.)

      (O) "The right of individuals to control or influence what
      information related to them may be collected and stored and by
      whom and to whom that information may be disclosed." [I7498 Part
      2]

      (D) ISPDs SHOULD NOT use this term as a synonym for "data
      confidentiality" or "data confidentiality service", which are
      different concepts. Privacy is a reason for security rather than a
      kind of security. For example, a system that stores personal data
      needs to protect the data to prevent harm, embarrassment,
      inconvenience, or unfairness to any person about whom data is
      maintained, and to protect the person's privacy. For that reason,
      the system may need to provide data confidentiality service.

   $ Privacy Enhanced Mail (PEM)
      (I) An Internet protocol to provide data confidentiality, data
      integrity, and data origin authentication for electronic mail.
      [R1421, R1422]. (See: MOSS, MSP, PGP, S/MIME.)

      (C) PEM encrypts messages with DES in CBC mode; provides key
      distribution of DES keys by encrypting them with RSA; and signs
      messages with RSA and either MD2 or MD5. To establish ownership of
      public keys, PEM uses a certification hierarchy, with X.509
      public-key certificates and X.509 CRLs that are signed with RSA
      and MD2. (Compare with: Pretty Good Privacy.)

      (C) PEM is designed to be compatible with a wide range of key
      management methods, but is limited by specifying security services
      only for text messages and, like MOSS, has not been widely
      implemented in the Internet.

   $ private component
      (I) A synonym for "private key".

      (D) In most cases, ISPDs SHOULD NOT use this term; to avoid
      confusing readers, use "private key" instead. However, the term
      MAY be used when specifically discussing a key pair; e.g., "A key
      pair has a public component and a private component."

   $ private extension
      See: (secondary definition in) extension.

   $ private key
      (I) The secret component of a pair of cryptographic keys used for
      asymmetric cryptography. (See: key pair, public key.)



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      (O) "(In a public key cryptosystem) that key of a user's key pair
      which is known only by that user." [X509]

   $ privilege
      (I) An authorization or set of authorizations to perform security-
      relevant functions, especially in the context of a computer
      operating system.

   $ privilege management infrastructure
      (N) "The complete set of processes required to provide an
      authorization service" [i.e., processes concerned with attribute
      certificates]. [FPDAM]

      (D) ISPDs SHOULD NOT use this term and its definition because the
      definition is vague, and there is no consensus on an alternate
      definition.

   $ privileged process
      (I) An computer process that is authorized (and, therefore,
      trusted) to perform some security-relevant functions that ordinary
      processes are not. (See: privilege, trusted process.)

   $ procedural security
      (D) ISPDs SHOULD NOT use this term as a synonym for
      "administrative security". Any type of security may involve
      procedures; therefore, the term may be misleading. Instead, use
      "administrative security", "communication security", "computer
      security", "emanations security", "personnel security", "physical
      security", or whatever specific type is meant. (See: security
      architecture.)

   $ proprietary
      (I) Refers to information (or other property) that is owned by an
      individual or organization and for which the use is restricted by
      that entity.

   $ protected checksum
      (I) A checksum that is computed for a data set by means that
      protect against active attacks that would attempt to change the
      checksum to make it match changes made to the data set. (See:
      digital signature, keyed hash, (discussion under) checksum.

   $ protected distribution system
      (I) A wireline or fiber-optic system that includes sufficient
      safeguards (acoustic, electric, electromagnetic, and physical) to
      permit its use for unencrypted transmission of (cleartext) data.

   $ protection authority
      See: (secondary definition in) Internet Protocol Security Option.

   $ protection ring
      (I) One of a hierarchy of privileged operation modes of a system


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      that gives certain access rights to processes authorized to
      operate in that mode.

   $ protocol
      (I) A set of rules (i.e., formats and procedures) to implement and
      control some type of association (e.g., communication) between
      systems. (For example, see: Internet Protocol.)

      (C) In particular, a series of ordered steps involving computing
      and communication that are performed by two or more system
      entities to achieve a joint objective. [A9042]

   $ protocol suite
      (I) A complementary collection of communication protocols used in
      a computer network. (See: Internet, OSI.)

   $ proxy server
      (I) A computer process--often used as, or as part of, a firewall--
      that relays a protocol between client and server computer systems,
      by appearing to the client to be the server and appearing to the
      server to be the client. (See: SOCKS.)

      (C) In a firewall, a proxy server usually runs on a bastion host,
      which may support proxies for several protocols (e.g., FTP, HTTP,
      and TELNET). Instead of a client in the protected enclave
      connecting directly to an external server, the client connects to
      the proxy server which in turn connects to the external server.
      The proxy server waits for a request from inside the firewall,
      forwards the request to the remote server outside the firewall,
      gets the response, then sends the response back to the client. The
      proxy may be transparent to the clients, or they may need to
      connect first to the proxy server, and then use that association
      to also initiate a connection to the real server.

      (C) Proxies are generally preferred over SOCKS for their ability
      to perform caching, high-level logging, and access control. A
      proxy can provide security service beyond that which is normally
      part of the relayed protocol, such as access control based on peer
      entity authentication of clients, or peer entity authentication of
      servers when clients do not have that capability. A proxy at OSI
      layer 7 can also provide finer-grained security service than can a
      filtering router at OSI layer 3. For example, an FTP proxy could
      permit transfers out of, but not into, a protected network, or
      vice versa.

   $ pseudo-random
      (I) A sequence of values that appears to be random (i.e.,
      unpredictable) but is actually generated by a deterministic
      algorithm.

   $ pseudo-random number generator
      (I) A process used to deterministically generate a series of


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      numbers (usually integers) that appear to be random according to
      certain statistical tests, but actually are pseudo-random.

      (C) Pseudo-random number generators are usually implemented in
      software.

   $ public component
      (D) ISPDs SHOULD NOT use this term as a synonym for "public key"
      except when discussing a key pair.

   $ public key
      (I) The publicly-disclosable component of a pair of cryptographic
      keys used for asymmetric cryptography. (See: key pair, private
      key.)

      (O) "(In a public key cryptosystem) that key of a user's key pair
      which is publicly known." [X509]

   $ public-key certificate
      (I) A digital certificate that binds a system entity's identity to
      a public key value, and possibly to additional data items; a
      digitally-signed data structure that attests to the ownership of a
      public key. (See: X.509 public-key certificate.)

      (C) The digital signature on a public-key certificate is
      unforgeable. Thus, the certificate can be published, such as by
      posting it in a directory, without the directory having to protect
      the certificate's data integrity.

      (O) "The public key of a user, together with some other
      information, rendered unforgeable by encipherment with the private
      key of the certification authority which issued it." [X509]

   $ public-key cryptography
      (I) The popular synonym for "asymmetric cryptography".

   $ Public-Key Cryptography Standards (PKCS)
      (I) A series of specifications published by RSA Laboratories for
      data structures and algorithm usage for basic applications of
      asymmetric cryptography. (See: PKCS #7, PKCS #10, PKCS #11.)

      (C) The PKCS were begun in 1991 in cooperation with industry and
      academia, originally including Apple, Digital, Lotus, Microsoft,
      Northern Telecom, Sun, and MIT. Today, these specifications are
      widely used, but they are not sanctioned by an official standards
      organizations, such as ANSI and ITU-T. RSA Laboratories retains
      sole decision-making authority over the PKCS.

   $ public-key forward secrecy (PFS)
      (I) For a key agreement protocol based on asymmetric cryptography,
      the property that ensures that a session key derived from a set of
      long-term public and private keys will not be compromised if one


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      of the private keys is compromised in the future.

      (C) Some existing RFCs use the term "perfect forward secrecy" but
      either do not define it or do not define it precisely. While
      preparing this Glossary, we tried to find a good definition for
      that term, but found this to be a muddled area. Experts did not
      agree. For all practical purposes, the literature defines "perfect
      forward secrecy" by stating the Diffie-Hellman algorithm. The term
      "public-key forward secrecy" (suggested by Hilarie Orman) and the
      "I" definition stated for it here were crafted to be compatible
      with current Internet documents, yet be narrow and leave room for
      improved terminology.

      (C) Challenge to the Internet security community: We need a
      taxonomy--a family of mutually exclusive and collectively
      exhaustive terms and definitions to cover the basic properties
      discussed here--for the full range of cryptographic algorithms and
      protocols used in Internet Standards:

      (C) Involvement of session keys vs. long-term keys: Experts
      disagree about the basic ideas involved.

       - One concept of "forward secrecy" is that, given observations of
      the operation of a key establishment protocol up to time t, and
      given some of the session keys derived from those protocol runs,
      you cannot derive unknown past session keys or future session
      keys.

       - A related property is that, given observations of the protocol
      and knowledge of the derived session keys, you cannot derive one
      or more of the long-term private keys.

       - The "I" definition presented above involves a third concept of
      "forward secrecy" that refers to the effect of the compromise of
      long-term keys.

       - All three concepts involve the idea that a compromise of "this"
      encryption key is not supposed to compromise the "next" one. There
      also is the idea that compromise of a single key will compromise
      only the data protected by the single key. In Internet literature,
      the focus has been on protection against decryption of back
      traffic in the event of a compromise of secret key material held
      by one or both parties to a communication.

      (C) Forward vs. backward: Experts are unhappy with the word
      "forward", because compromise of "this" encryption key also is not
      supposed to compromise the "previous" one. In S/KEY, if the key
      used at time t is compromised, then all keys used prior to that
      are compromised. If the "long-term" key (i.e., the base of the
      hashing scheme) is compromised, then all keys past and future are
      compromised; thus, you could say that S/KEY has neither forward
      nor backward secrecy.


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      (C) Asymmetric cryptography vs. symmetric: Experts disagree about
      forward secrecy in the context of symmetric cryptographic systems.
      In the absence of asymmetric cryptography, compromise of any long-
      term key seems to compromise any session key derived from the
      long-term key. For example, Kerberos isn't forward secret, because
      compromising a client's password (thus compromising the key shared
      by the client and the authentication server) compromises future
      session keys shared by the client and the ticket-granting server.

      (C) Ordinary forward secrecy vs. "perfect" forward secret: Experts
      disagree about the difference between these two. Some say there is
      no difference. Others say that the initial naming was unfortunate
      and suggest dropping the word "perfect". Some suggest using
      "forward secrecy" for the case where one long-term private key is
      compromised, and adding "perfect" for when both private keys (or,
      when the protocol is multi-party, all private keys) are
      compromised.

      (C) Acknowledgements: Bill Burr, Burt Kaliski, Steve Kent, Paul
      Van Oorschot, Michael Wiener, and, especially, Hilarie Orman
      contributed ideas to this discussion.

   $ public-key infrastructure (PKI)
      (I) A system of CAs (and, optionally, RAs and other supporting
      servers and agents) that perform some set of certificate
      management, archive management, key management, and token
      management functions for a community of users in an application of
      asymmetric cryptography. (See: hierarchical PKI, mesh PKI,
      security management infrastructure, trust-file PKI.)

      (O) PKIX usage: The set of hardware, software, people, policies,
      and procedures needed to create, manage, store, distribute, and
      revoke digital certificates based on asymmetric cryptography.

      (C) The core PKI functions are to register users and issue their
      public-key certificates, revoke certificates when required, and
      archive data needed to validate certificates at a much later time.
      Key pairs may be generated by CAs or RAs, but requiring a PKI
      client to generate its own digital signature key pair helps
      maintain system integrity of the cryptographic system, because
      then only the client ever possesses the private key it uses. Also,
      an authority may be established to approve or coordinate CPSs,
      which are security policies under which components of a PKI
      operate.

      (C) A number of other servers and agents may support the core PKI,
      and PKI clients may obtain services from them. The full range of
      such services is not yet fully understood and is evolving, but
      supporting roles may include archive agent, certified delivery
      agent, confirmation agent, digital notary, directory, key escrow
      agent, key generation agent, naming agent who ensures that issuers


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      and subjects have unique identifiers within the PKI, repository,
      ticket-granting agent, and time stamp agent.

   $ RA
      See: registration authority.

   $ RA domains
      (I) A capability of a CAW that allows a CA to divide the
      responsibility for certificate requests among multiple RAs.

      (C) This capability might be used to restrict access to private
      authorization data that is provided with a certificate request;
      and distribute the responsibility to review and approve
      certificate requests in high volume environments among multiple
      RAs. RA domains might segregate certificate requests according to
      an attribute of the certificate subject, such as an organizational
      unit

   $ RADIUS
      See: Remote Authentication Dial-In User Service.

   $ Rainbow Series
      (O) A set of more than 30 technical and policy documents with
      colored covers, issued by the NCSC, that discuss in detail the
      TCSEC and provide guidance for meeting and applying the criteria.
      (See: Green Book, Orange Book, Red Book, Yellow Book.)

   $ random
      (I) In essence, random means unpredictable. A sequence of values
      is called random if each successive value is obtained merely by
      chance and does not depend on the preceding values of the
      sequence, and each individual value is called random if each of
      the values in the total population of possibilities has equal
      probability of being selected. (See: cryptographic key, pseudo-
      random.)

   $ random number generator
      (I) A process used to generate an unpredictable, uniformly
      distributed series of numbers (usually integers). (See: pseudo-
      random, random.)

      (C) True random number generators are hardware-based devices that
      depend on the output of a "noisy diode" or other physical
      phenomena. [R1750]

   $ RBAC
      See: Role-Based Access Control.

   $ RC2
   $ RC4
      See: Rivest Cipher #2, Rivest Cipher #4.



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   $ realm
      (O) Kerberos usage: The domain of authority of a Kerberos server
      (consisting of an authentication server and a ticket-granting
      server), including the Kerberized clients and the Kerberized
      application servers

   $ RED
      (I) Designation for information system equipment or facilities
      that handle (and for data that contains) only plaintext (or,
      depending on the context, classified information), and for such
      data itself. This term derives from U.S. Government COMSEC
      terminology. (Compare with: BLACK. Also see: RED/BLACK
      separation.)

   $ Red Book
      (D) ISPDs SHOULD NOT use this term as a synonym for "Trusted
      Network Interpretation of the Trusted Computer System Evaluation
      Criteria" [NCS05]. Instead, use the full proper name of the
      document or, in subsequent references, a more conventional
      abbreviation. (See: TCSEC, Rainbow Series, (usage note under)
      Green Book.)

   $ RED/BLACK separation
      (I) An architectural concept for cryptographic systems that
      strictly separates the parts of a system that handle plaintext
      (RED information) from the parts that handle ciphertext (BLACK
      information). This term derives from U.S. Government COMSEC
      terminology. (See: BLACK, RED.)

   $ reference monitor
      (I) "An access control concept that refers to an abstract machine
      that mediates all accesses to objects by subjects." [NCS04]

      (C) A reference monitor should be (1) complete (i.e., it mediates
      every access), (2) isolated (i.e., it cannot be modified by other
      system entities), and (3) verifiable. (See: security kernel.)

   $ reflection attack
      (I) A type of replay attack in which transmitted data is sent back
      to its originator.

   $ register
   $ registration
      (I) An administrative act or process whereby an entity's name and
      other attributes are established for the first time at a CA, prior
      to the CA issuing a digital certificate that has the entity's name
      as the subject. (See: registration authority.)

      (C) Registration can be accomplished either directly, by the CA,
      or indirectly, by a separate RA. An entity is presented to the CA
      or RA, and the authority either records the name(s) claimed for
      the entity or assigns the entity's name(s). The authority also


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      determines and records other attributes of the entity that are to
      be bound in a certificate (such as a public key or authorizations)
      or maintained in the authority's database (such as street address
      and telephone number). The authority is responsible, possibly
      assisted by an RA, for authenticating the entity's identity and
      verifying the correctness of the other attributes, in accordance
      with the CA's CPS.

      (C) Among the registration issues that a CPS may address are the
      following [R2527]:

       - How a claimed identity and other attributes are verified.
       - How organization affiliation or representation is verified.
       - What forms of names are permitted, such as X.500 DN, domain
         name, or IP address.
       - Whether names are required to be meaningful or unique, and
         within what domain.
       - How naming disputes are resolved, including the role of
         trademarks.
       - Whether certificates are issued to entities that are not
         persons.
       - Whether a person is required to appear before the CA or RA, or
         can instead be represented by an agent.
       - Whether and how an entity proves possession of the private key
         matching a public key.

   $ registration authority (RA)
      (I) An optional PKI entity (separate from the CAs) that does not
      sign either digital certificates or CRLs but has responsibility
      for recording or verifying some or all of the information
      (particularly the identities of subjects) needed by a CA to issue
      certificates and CRLs and to perform other certificate management
      functions. (See: organizational registration authority,
      registration.)

      (C) Sometimes, a CA may perform all certificate management
      functions for all end users for which the CA signs certificates.
      Other times, such as in a large or geographically dispersed
      community, it may be necessary or desirable to offload secondary
      CA functions and delegate them to an assistant, while the CA
      retains the primary functions (signing certificates and CRLs). The
      talks that are delegated to an RA by a CA may include personal
      authentication, name assignment, token distribution, revocation
      reporting, key generation, and archiving. An RA is an optional PKI
      component, separate from the CA, that is assigned secondary
      functions. The duties assigned to RAs vary from case to case but
      may include the following:

       - Verifying a subject's identity, i.e., performing personal
         authentication functions.
       - Assigning a name to a subject. (See: distinguished name.)
       - Verifying that a subject is entitled to have the attributes


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         requested for a certificate.
       - Verifying that a subject possesses the private key that matches
         the public key requested for a certificate.
       - Performing functions beyond mere registration, such as
         generating key pairs, distributing tokens, and handling
         revocation reports. Such functions may also be assigned to a
         PKI element that is separate from both the CA and the RA.

      (I) PKIX usage: An optional PKI component, separate from the
      CA(s). The functions which the RA may carry out will vary from
      case to case but may include personal authentication, token
      distribution, revocation reporting, name assignment, key
      generation, and archiving of key pairs. [R2510]

      (O) SET usage: "An independent third-party organization that
      processes payment card applications for multiple payment card
      brands and forwards applications to the appropriate financial
      institutions." [SET2]

   $ regrade
      (I) Deliberately change the classification level of information in
      an authorized manner.

   $ rekey
      (I) Change the value of a cryptographic key that is being used in
      an application of a cryptographic system. (See: certificate
      rekey.)

      (C) For example, rekey is required at the end of a cryptoperiod or
      key lifetime.

   $ reliability
      (I) The ability of a system to perform a required function under
      stated conditions for a specified period of time. (See:
      availability, survivability.)

   $ relying party
      (I) A synonym for "certificate user". Used in a legal context
      (see: ABA Guidelines) to mean a recipient of a certificate who
      acts in reliance on that certificate.

   $ Remote Authentication Dial-In User Service (RADIUS)
      (I) An Internet protocol for carrying dial-in users'
      authentication information and configuration information between a
      shared, centralized authentication server (the RADIUS server) and
      a network access server (the RADIUS client) that needs to
      authenticate the users of its network access ports. [R2138] (See:
      TACACS.)

      (C) A user of the RADIUS client presents authentication
      information to the client, and the client passes that information
      to the RADIUS server. The server authenticates the client using a


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      shared secret value, then checks the user's authentication
      information, and finally returns to the client all authorization
      and configuration information needed by the client to deliver
      service to the user.

   $ renew
      See: certificate renewal.

   $ replay attack
      (I) An attack in which a valid data transmission is maliciously or
      fraudulently repeated, either by the originator or by an adversary
      who intercepts the data and retransmits it, possibly as part of a
      masquerade attack. (See: active wiretapping.)

   $ repository
      (I) A system for storing and distributing digital certificates and
      related information (including CRLs, CPSs, and certificate
      policies) to certificate users. (See: directory.)

      (O) "A trustworthy system for storing and retrieving certificates
      or other information relevant to certificates." [ABA]

      (C) A certificate is published to those who might need it by
      putting it in a repository. The repository usually is a publicly
      accessible, on-line server. In the Federal Public-key
      Infrastructure, for example, the expected repository is a
      directory that uses LDAP, but also may be the X.500 Directory that
      uses DAP, or an HTTP server, or an FTP server that permits
      anonymous login.

   $ repudiation
      (I) Denial by a system entity that was involved in an association
      (especially an association that transfers information) of having
      participated in the relationship. (See: accountability, non-
      repudiation service.)

      (O) "Denial by one of the entities involved in a communication of
      having participated in all or part of the communication." [I7498
      Part 2]

   $ Request for Comment (RFC)
      (I) One of the documents in the archival series that is the
      official channel for ISPDs and other publications of the Internet
      Engineering Steering Group, the Internet Architecture Board, and
      the Internet community in general. [R1543]

      (C) This term does not mean the same as "Internet Standard".

   $ residual risk
      (I) The risk that remains after countermeasures have been applied.




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   $ restore
      See: card restore.

   $ revocation
      See: certificate revocation.

   $ revocation date
      (N) In an X.509 CRL entry, a date-time field that states when the
      certificate revocation occurred, i.e., when the CA declared the
      digital certificate to be invalid. (See: invalidity date.)

      (C) The revocation date may not resolve some disputes because, in
      the worst case, all signatures made during the validity period of
      the certificate may have to be considered invalid. However, it may
      be desirable to treat a digital signature as valid even though the
      private key used to sign was compromised after the signing. If
      more is known about when the compromise actually occurred, a
      second date-time, an "invalidity date", can be included in an
      extension of the CRL entry.

   $ revocation list
      See: certificate revocation list.

   $ revoke
      See: certificate revocation.

   $ RFC
      See: Request for Comment.

   $ risk
      (I) An expectation of loss expressed as the probability that a
      particular threat will exploit a particular vulnerability with a
      particular harmful result.

      (O) SET usage: "The possibility of loss because of one or more
      threats to information (not to be confused with financial or
      business risk)." [SET2]

   $ risk analysis
   $ risk assessment
      (I) A process that systematically identifies valuable system
      resources and threats to those resources, quantifies loss
      exposures (i.e., loss potential) based on estimated frequencies
      and costs of occurrence, and (optionally) recommends how to
      allocate resources to countermeasures so as to minimize total
      exposure.

      (C) The analysis lists risks in order of cost and criticality,
      thereby determining where countermeasures should be applied first.
      It is usually financially and technically infeasible to counteract
      all aspects of risk, and so some residual risk will remain, even
      after all available countermeasures have been deployed. [FP031,


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      R2196]

   $ risk management
      (I) The process of identifying, controlling, and eliminating or
      minimizing uncertain events that may affect system resources.
      (See: risk analysis.)

   $ Rivest Cipher #2 (RC2)
      (N) A proprietary, variable-key-length block cipher invented by
      Ron Rivest for RSA Data Security, Inc. (now a wholly-owned
      subsidiary of Security Dynamics, Inc.).

   $ Rivest Cipher #4 (RC4)
      (N) A proprietary, variable-key-length stream cipher invented by
      Ron Rivest for RSA Data Security, Inc. (now a wholly-owned
      subsidiary of Security Dynamics, Inc.).

   $ Rivest-Shamir-Adleman (RSA)
      (N) An algorithm for asymmetric cryptography, invented in 1977 by
      Ron Rivest, Adi Shamir, and Leonard Adleman [RSA78].

      (C) RSA uses exponentiation modulo the product of two large prime
      numbers. The difficulty of breaking RSA is believed to be
      equivalent to the difficulty of factoring integers that are the
      product of two large prime numbers of approximately equal size.

      (C) To create an RSA key pair, randomly choose two large prime
      numbers, p and q, and compute the modulus, n = pq. Randomly choose
      a number e, the public exponent, that is less than n and
      relatively prime to (p-1)(q-1). Choose another number d, the
      private exponent, such that ed-1 evenly divides (p-1)(q-1). The
      public key is the set of numbers (n,e), and the private key is the
      set (n,d).

      (C) It is assumed to be difficult to compute the private key (n,d)
      from the public key (n,e). However, if n can be factored into p
      and q, then the private key d can be computed easily. Thus, RSA
      security depends on the assumption that it is computationally
      difficult to factor a number that is the product of two large
      prime numbers. (Of course, p and q are treated as part of the
      private key, or else destroyed after computing n.)

      (C) For encryption of a message, m, to be sent to Bob, Alice uses
      Bob's public key (n,e) to compute m**e (mod n) = c. She sends c to
      Bob. Bob computes c**d (mod n) = m. Only Bob knows d, so only Bob
      can compute c**d (mod n) = m to recover m.

      (C) To provide data origin authentication of a message, m, to be
      sent to Bob, Alice computes m**d (mod n) = s, where (d,n) is
      Alice's private key. She sends m and s to Bob. To recover the
      message that only Alice could have sent, Bob computes s**e (mod n)
      = m, where (e,n) is Alice's public key.


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      (C) To ensure data integrity in addition to data origin
      authentication requires extra computation steps in which Alice and
      Bob use a cryptographic hash function h (as explained for digital
      signature). Alice computes the hash value h(m) = v, and then
      encrypts v with her private key to get s. She sends m and s. Bob
      receives m' and s', either of which might have been changed from
      the m and s that Alice sent. To test this, he decrypts s' with
      Alice's public key to get v'. He then computes h(m') = v". If v'
      equals v", Bob is assured that m' is the same m that Alice sent.

   $ role-based access control (RBAC)
      (I) A form of identity-based access control where the system
      entities that are identified and controlled are functional
      positions in an organization or process.

   $ root
      (I) A CA that is directly trusted by an end entity. Acquiring the
      value of a root CA's public key requires an out-of-band procedure.

      (I) Hierarchical PKI usage: The CA that is the highest level (most
      trusted) CA in a certification hierarchy; i.e., the authority upon
      whose public key all certificate users base their trust. (See: top
      CA.)

      (C) In a hierarchical PKI, a root issues public-key certificates
      to one or more additional CAs that form the second highest level.
      Each of these CAs may issue certificates to more CAs at the third
      highest level, and so on. To initialize operation of a
      hierarchical PKI, the root's initial public key is securely
      distributed to all certificate users in a way that does not depend
      on the PKI's certification relationships. The root's public key
      may be distributed simply as a numerical value, but typically is
      distributed in a self-signed certificate in which the root is the
      subject. The root's certificate is signed by the root itself
      because there is no higher authority in a certification hierarchy.
      The root's certificate is then the first certificate in every
      certification path.

      (O) MISSI usage: A name previously used for a MISSI Policy
      Creation Authority, which is not a root as defined above for
      general usage, but is a CA at the second level of the MISSI
      hierarchy, immediately subordinate to a MISSI root called a Policy
      Approving Authority.

      (O) UNIX usage: A system user account (also called "superuser")
      that has all privileges (including all security-related
      privileges) and thus can manage the system and its other user
      accounts.

   $ root certificate
      (I) A certificate for which the subject is a root.


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      (I) Hierarchical PKI usage: The self-signed public-key certificate
      at the top of a certification hierarchy.

   $ root key
      (I) A public key for which the matching private key is held by a
      root.

   $ root registry
      (O) MISSI usage: A name previously used for a MISSI policy
      approving authority.

   $ router
      (I) A computer that is a gateway between two networks at OSI layer
      3 and that relays and directs data packets through that
      internetwork. The most common form of router operates on IP
      packets. (See: bridge.)

      (I) Internet usage: In the context of the Internet protocol suite,
      a networked computer that forwards Internet Protocol packets that
      are not addressed to the computer itself. (Compare with: host.)

   $ RSA
      See: Rivest-Shamir-Adleman.

   $ rule-based security policy
      (I) "A security policy based on global rules imposed for all
      users. These rules usually rely on comparison of the sensitivity
      of the resource being accessed and the possession of corresponding
      attributes of users, a group of users, or entities acting on
      behalf of users." [I7498 Part 2] (See: identity-based security
      policy.)

   $ safety
      (I) The property of a system being free from risk of causing harm
      to system entities and outside entities.

   $ SAID
      See: security association identifier.

   $ salt
      (I) A random value that is concatenated with a password before
      applying the one-way encryption function used to protect passwords
      that are stored in the database of an access control system. (See:
      initialization value.)

      (C) Salt protects a password-based access control system against a
      dictionary attack.

   $ sanitize
      (I) Delete sensitive data from a file, a device, or a system; or
      modify data so as to be able to downgrade its classification


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      level.

   $ SASL
      See: Simple Authentication and Security Layer.

   $ SCA
      See: subordinate certification authority.

   $ scavenging
      See: (secondary threat action definition in) threat consequence.

   $ screening router
      (I) A synonym for "filtering router".

   $ SDE
      See: Secure Data Exchange.

   $ SDNS
      See: Secure Data Network System.

   $ seal
      (D) To use cryptography to provide data integrity service for a
      data set. (See: checksum, sign, wrap.)

      (C) ISPDs SHOULD NOT use this definition; instead, use language
      that is more specific with regard to the mechanism(s) used.

   $ secrecy
   $ secret
      (I) The condition of information being protected from being known
      by any system entities except those who are intended to know it;
      an item of information that is so protected.

      (C) This term applies to symmetric keys, private keys, and
      passwords.

   $ secret-key cryptography
      (I) A synonym for "symmetric cryptography".

   $ Secure Data Exchange (SDE)
      (N) A local area network security protocol defined by the IEEE
      802.10 standard.

   $ Secure Data Network System (SDNS)
      (N) An NSA program that developed security a for electronic mail
      (Message Security Protocol), OSI layer 3 (SP3), OSI layer 4 (SP4),
      and key management (KMP).

   $ Secure Hash Standard (SHS)
      (N) The U.S. Government standard [FP180] that specifies the Secure
      Hash Algorithm (SHA-1), a cryptographic hash function that
      produces a 160-bit output (hash result) for input data of any


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      length < 2**64 bits.

   $ Secure Hypertext Transfer Protocol (Secure-HTTP, S-HTTP)
      (I) A Internet protocol for providing client-server security
      services for HTTP communications. (Compare with: https.)

      (C) S-HTTP was originally specified by CommerceNet, a coalition of
      businesses interested in developing the Internet for commercial
      uses. Several message formats may be incorporated into S-HTTP
      clients and servers, particularly CMS and MOSS. S-HTTP supports
      choice of security policies, key management mechanisms, and
      cryptographic algorithms through option negotiation between
      parties for each transaction. S-HTTP supports both asymmetric and
      symmetric key operation modes. S-HTTP attempts to avoid presuming
      a particular trust model, but it attempts to facilitate multiply-
      rooted hierarchical trust and anticipates that principals may have
      many public key certificates.

   $ Secure/MIME (S/MIME)
      (I) Secure/Multipurpose Internet Mail Extensions, an Internet
      protocol developed by an industry consortium led by RSA Data
      Security, Inc. (which is now a subsidiary of Security Dynamics
      Technologies, Inc.). [R2633]

   $ Secure Sockets Layer (SSL)
      (N) An Internet protocol (originally developed by Netscape
      Communications, Inc.) that uses connection-oriented end-to-end
      encryption to provide data confidentiality service and data
      integrity service for traffic between a client (often a web
      browser) and a server, and that can optionally provide peer entity
      authentication between the client and the server. (See: Transport
      Layer Security.)

      (C) SSL is layered below HTTP (other Internet applications, such
      as FTP, would be better served by IPsec) and above a reliable
      transport protocol (TCP). SSL is independent of the application it
      encapsulates, and a higher level protocol can layer on top of SSL
      transparently. SSL itself has two layers: (a) SSL's lower layer,
      the SSL Record Protocol, is layered on top of the transport
      protocol and encapsulates higher level protocols. One such
      encapsulated protocol is SSL Handshake Protocol. (b) SSL's upper
      layer provides asymmetric cryptography for server authentication
      (verifying the server's identity to the client) and optional
      client authentication (verifying the client's identity to the
      server), and also enables them to negotiate a symmetric encryption
      algorithm and secret session key (to use for data confidentiality)
      before the application protocol transmits or receives data. A
      keyed hash provides data integrity service for encapsulated data.

   $ secure state
      (I) A system condition in which no subject can access any object
      in an unauthorized manner. (See: (secondary definition in) Bell-


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      LaPadula Model, clean system.)

   $ security
      (I) (1.) Measures taken to protect a system. (2.) The condition of
      a system that results from the establishment and maintenance of
      measures to protect the system. (3.) The condition of system
      resources being free from unauthorized access and from
      unauthorized or accidental change, destruction, or loss.

   $ security architecture
      (I) A plan and set of principles that describe (a) the security
      services that a system is required to provide to meet the needs of
      its users, (b) the system elements required to implement the
      services, and (c) the performance levels required in the elements
      to deal with the threat environment. (See: (discussion under)
      security policy.)

      (C) A security architecture is the result of applying the system
      engineering process. A complete system security architecture
      includes administrative security, communication security, computer
      security, emanations security, personnel security, and physical
      security (e.g., see: [R2179]). A complete security architecture
      needs to deal with both intentional, intelligent threats and
      accidental kinds of threats.

   $ security association
      (I) A relationship defined between two or more entities to enable
      them to protect data they exchange. The relationship is used to
      negotiate characteristics of protection mechanisms, but does not
      include the mechanisms themselves. (See: association.)

      (C) A security association describes how entities will use
      security services. The relationship is represented by a set of
      information that is shared between the entities and is agreed upon
      and considered a contract between them.

      (O) IPsec usage. A simplex (uni-directional) logical connection
      created for security purposes and implemented with either AH or
      ESP (but not both), which provide security services to data
      carried by a connection. The security services offered by a
      security association depend on the protocol selected, the IPsec
      mode (transport or tunnel), the endpoints, and the election of
      optional services within the protocol. A security association is
      identified by a triple consisting of a destination IP address, a
      protocol (AH or ESP) identifier, and a Security Parameter Index.

   $ security association identifier (SAID)
      (I) A data field in a security protocol (such as NLSP or SDE),
      used to identify the security association to which a protocol data
      unit is bound. The SAID value is usually used to select a key to
      use for decryption or authentication at the destination. (See:
      Security Parameter Index.)


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   $ security audit
      (I) An independent review and examination of a system's records
      and activities to determine the adequacy of system controls,
      ensure compliance with established security policy and procedures,
      detect breaches in security services, and recommend any changes
      that are indicated for countermeasures. [I7498 Part 2, NCS01]

      (C) The basic audit objective is to establish accountability for
      system entities that initiate or participate in security-relevant
      events and actions. Thus, means are needed to generate and record
      a security audit trail and to review and analyze the audit trail
      to discover and investigate attacks and security compromises.

   $ security audit trail
      (I) A chronological record of system activities that is sufficient
      to enable the reconstruction and examination of the sequence of
      environments and activities surrounding or leading to an
      operation, procedure, or event in a security-relevant transaction
      from inception to final results. [NCS04] (See: security audit.)

   $ security class
      (D) A synonym for "security level". In the interest of
      consistency, ISPDs SHOULD use "security level" instead of
      "security class".

   $ security clearance
      (I) A determination that a person is eligible, under the standards
      of a specific security policy, for authorization to access
      sensitive information or other system resources. (See: clearance
      level.)

   $ security compromise
      (I) A security violation in which a system resource is exposed, or
      is potentially exposed, to unauthorized access. (See: data
      compromise, violation.)

   $ security environment
      (I) The set of external entities, procedures, and conditions that
      affect secure development, operation, and maintenance of a system.

   $ security event
      (I) A occurrence in a system that is relevant to the security of
      the system.

      (C) The term includes both events that are security incidents and
      those that are not. In a CA workstation, for example, a list of
      security events might include the following:

       - Performing a cryptographic operation, e.g., signing a digital
         certificate or CRL.
       - Performing a cryptographic card operation: creation, insertion,


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         removal, or backup.
       - Performing a digital certificate lifecycle operation: rekey,
         renewal, revocation, or update.
       - Posting information to an X.500 Directory.
       - Receiving a key compromise notification.
       - Receiving an improper certification request.
       - Detecting an alarm condition reported by a cryptographic
         module.
       - Logging the operator in or out.
       - Failing a built-in hardware self-test or a software system
         integrity check.

   $ security fault analysis
      (I) A security analysis, usually performed on hardware at a logic
      gate level, gate-by-gate, to determine the security properties of
      a device when a hardware fault is encountered.

   $ security gateway
      (I) A gateway that separates trusted (or relatively more trusted)
      hosts on the internal network side from untrusted (or less
      trusted) hosts on the external network side. (See: firewall and
      guard.)

      (O) IPsec usage: "An intermediate system that implements IPsec
      protocols." [R2401] Normally, AH or ESP is implemented to serve a
      set of internal hosts, providing security services for the hosts
      when they communicate with other, external hosts or gateways that
      also implement IPsec.

   $ security incident
      (I) A security event that involves a security violation. (See:
      CERT, GRIP, security event, security violation.)

      (C) In other words, a security-relevant event in a system in which
      the system's security policy is disobeyed or otherwise breached.

      (O) "Any adverse event which compromises some aspect of computer
      or network security." [R2350]

      (D) ISPDs SHOULD NOT use this "O" definition because (a) a
      security incident may occur without actually being harmful (i.e.,
      adverse) and (b) this Glossary defines "compromise" more narrowly
      in relation to unauthorized access.

   $ security intrusion
      (I) A security event, or a combination of multiple security
      events, that constitutes a security incident in which an intruder
      gains, or attempts to gain, access to a system (or system
      resource) without having authorization to do so.

   $ security kernel
      (I) "The hardware, firmware, and software elements of a trusted


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      computing base that implement the reference monitor concept. It
      must mediate all accesses, be protected from modification, and be
      verifiable as correct." [NCS04] (See: reference monitor.)

      (C) That is, a security kernel is an implementation of a reference
      monitor for a given hardware base.

   $ security label
      (I) A marking that is bound to a system resource and that names or
      designates the security-relevant attributes of that resource.
      [I7498 Part 2, R1457]

      (C) The recommended definition is usefully broad, but usually the
      term is understood more narrowly as a marking that represents the
      security level of an information object, i.e., a marking that
      indicates how sensitive an information object is. [NCS04]

      (C) System security mechanisms interpret security labels according
      to applicable security policy to determine how to control access
      to the associated information, otherwise constrain its handling,
      and affix appropriate security markings to visible (printed and
      displayed) images thereof. [FP188]

   $ security level
      (I) The combination of a hierarchical classification level and a
      set of non-hierarchical category designations that represents how
      sensitive information is. (See: dominate, lattice model.)

   $ security management infrastructure (SMI)
      (I) System elements and activities that support security policy by
      monitoring and controlling security services and mechanisms,
      distributing security information, and reporting security events.
      The associated functions are as follows [I7498-4]:

       - Controlling (granting or restricting) access to system
      resources: This includes verifying authorizations and
      identities, controlling access to sensitive security data, and
      modifying access priorities and procedures in the event of
      attacks.

       - Retrieving (gathering) and archiving (storing) security
      information: This includes logging security events and
      analyzing the log, monitoring and profiling usage, and
      reporting security violations.

       - Managing and controlling the encryption process: This includes
      performing the functions of key management and reporting on key
      management problems. (See: public-key infrastructure.)

   $ security mechanism
      (I) A process (or a device incorporating such a process) that can
      be used in a system to implement a security service that is


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      provided by or within the system. (See: (discussion under)
      security policy.)

      (C) Some examples of security mechanisms are encryption, digital
      signature, authentication exchange, and traffic padding.

   $ security model
      (I) A schematic description of a set of entities and relationships
      by which a specified set of security services are provided by or
      within a system. (See: (discussion under) security policy.)

      (C) An example is the Bell-LaPadula Model.
   $ security parameters index (SPI)
      (I) IPsec usage: The type of security association identifier used
      in IPsec protocols. A 32-bit value used to distinguish among
      different security associations terminating at the same
      destination (IP address) and using the same IPsec security
      protocol (AH or ESP). Carried in AH and ESP to enable the
      receiving system to determine under which security association to
      process a received packet.

   $ security perimeter
      (I) The boundary of the domain in which a security policy or
      security architecture applies; i.e., the boundary of the space in
      which security services protect system resources.

   $ security policy
      (I) A set of rules and practices that specify or regulate how a
      system or organization provides security services to protect
      sensitive and critical system resources. (See: identity-based
      security policy, rule-based security policy, security
      architecture, security mechanism, security model.)

      (O) "The set of rules laid down by the security authority
      governing the use and provision of security services and
      facilities." [X509]

      (C) Ravi Sandhu notes (as shown in the following diagram) that
      security policy is one of four layers of the security engineering
      process. Each provides a different view of security, ranging from
      what security services are needed to how services are implemented.













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         What Security Services Should Be Provided?
          ^
          | + - - - - - - - - - - - +
          | | Security Policy       |
          | + - - - - - - - - - - - +    |A "top-level specification"
          | | Security Model        |    |is generally understood to
          | + - - - - - - - - - - - + <- |be at a level below "model"
          | | Security Architecture |    |but above "architecture".
          | + - - - - - - - - - - - +
          | | Security Mechanism    |
          | + - - - - - - - - - - - +
          v
         How Are Security Services Implemented?

   $ Security Protocol 3 (SP3)
      (O) A protocol [SDNS3] developed by SDNS to provide connectionless
      data security at the top of OSI layer 3. (See: NLSP.)

   $ Security Protocol 4 (SP4)
      (O) A protocol [SDNS4] developed by SDNS to provide either
      connectionless or end-to-end connection-oriented data security at
      the bottom of OSI layer 4. (See: TLSP.)

   $ security-relevant event
      See: security event.

   $ security service
      (I) A processing or communication service that is provided by a
      system to give a specific kind of protection to system resources.
      (See: access control service, audit service, availability service,
      data confidentiality service, data integrity service, data origin
      authentication service, non-repudiation service, peer entity
      authentication service, system integrity service.)

      (O) "A service, provided by a layer of communicating open systems,
      which ensures adequate security of the systems or the data
      transfers." [I7498 Part 2]

      (C) Security services implement security policies, and are
      implemented by security mechanisms.

   $ security situation
      (I) ISAKMP usage: The set of all security-relevant information
      (e.g., network addresses, security classifications, manner of
      operation--normal or emergency) that is needed to decide the
      security services that are required to protect the association
      that is being negotiated.

   $ security token
      See: token.




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   $ security violation
      (I) An act or event that disobeys or otherwise breaches security
      policy. (See: compromise, penetration, security incident.)

   $ self-signed certificate
      (I) A public-key certificate for which the public key bound by the
      certificate and the private key used to sign the certificate are
      components of the same key pair, which belongs to the signer.

      (C) In a self-signed X.509 public-key certificate, the issuer's DN
      is the same as the subject's DN.

   $ semantic security
      (I) An attribute of a encryption algorithm that is a formalization
      of the notion that the algorithm not only hides the plaintext but
      also reveals no partial information about the plaintext. Whatever
      is efficiently computable about the plaintext when given the
      ciphertext, is also efficiently computable without the ciphertext.
      (See: indistinguishability.)

   $ sensitive (information)
      (I) Information is sensitive if disclosure, alteration,
      destruction, or loss of the information would adversely affect the
      interests or business of its owner or user. (See: critical.)

   $ separation of duties
      (I) The practice of dividing the steps in a system function among
      different individuals, so as to keep a single individual from
      subverting the process. (See: dual control, administrative
      security.)

   $ serial number
      See: certificate serial number.

   $ server
      (I) A system entity that provides a service in response to
      requests from other system entities called clients.

   $ session key
      (I) In the context of symmetric encryption, a key that is
      temporary or is used for a relatively short period of time. (See:
      key distribution center, master key.)

      (C) Usually, a session key is used for a defined period of
      communication between two computers, such as for the duration of a
      single connection or transaction set, or the key is used in an
      application that protects relatively large amounts of data and,
      therefore, needs to be rekeyed frequently.

   $ SET
      See: SET Secure Electronic Transaction(trademark).



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   $ SET private extension
      (O) One of the private extensions for X.509 that are defined by
      SET to carry information about a hashed root key, certificate
      types, merchant data, cardholder certificate requirements,
      encryption support for tunneling, or message support for payment
      instructions.

   $ SET qualifier
      (O) A certificate policy qualifier that provides information about
      the location and content of a SET certificate policy.

      (C) In addition to the policies and qualifiers inherited from its
      own certificate, each CA in the SET certification hierarchy may
      add one qualifying statement to the root policy when the CA issues
      a certificate. The additional qualifier is a certificate policy
      for that CA. Each policy in a SET certificate may have these
      qualifiers:

       - A URL where a copy of the policy statement may be found.
       - An electronic mail address where a copy of the policy statement
         may be found.
       - A hash result of the policy statement, computed using the
         indicated algorithm.
       - A statement declaring any disclaimers associated with the
         issuing of the certificate.

   $ SET Secure Electronic Transaction(trademark) or SET(trademark)
      (N) A protocol developed jointly by MasterCard International and
      Visa International and published as an open standard to provide
      confidentiality of transaction information, payment integrity, and
      authentication of transaction participants for payment card
      transactions over unsecured networks, such as the Internet. [SET]
      (See: acquirer, brand, cardholder, dual signature, electronic
      commerce, issuer, merchant, payment gateway, third party.)

      (C) This term and acronym are trademarks of SETCo. MasterCard and
      Visa announced the standard on February 1, 1996. On December 19,
      1997, MasterCard and Visa formed SET Secure Electronic Transaction
      LLC (commonly referred to as "SETCo") to implement the SET 1.0
      specification. A memorandum of understanding also has been signed
      that will eventually add American Express and JCB Credit Card
      Company as co-owners of SETCo.

   $ SETCo
      See: (secondary definition in) SET Secure Electronic Transaction.

   $ SHA-1
      See: Secure Hash Standard.

   $ shared secret
      (I) A synonym for "keying material" or "cryptographic key".



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   $ S-HTTP
      See: Secure HTTP.

   $ sign
      (I) Create a digital signature for a data set.

   $ signature
      See: digital signature, electronic signature.

   $ signer
      (N) A human being or an organization entity that creates a digital
      signature for a data set. [ABA]

   $ SILS
      See: Standards for Interoperable LAN/MAN Security.

   $ simple authentication
      (I) An authentication process that uses a password as the
      information that verifies an identity claimed for an entity. (See:
      strong authentication.)

      (O) "Authentication by means of simple password arrangements."
      [X509]

   $ Simple Authentication and Security Layer (SASL)
      (I) A specification [R2222] for adding authentication service to
      connection-based protocols. To use SASL, a protocol includes a
      command for authenticating a user to a server and for optionally
      negotiating protection of subsequent protocol interactions. The
      command names a registered security mechanism. SASL mechanisms
      include Kerberos, GSSAPI, S/KEY, and others. Some protocols that
      use SASL are IMAP4 and POP3.

   $ Simple Key-management for Internet Protocols (SKIP)
      (I) A key distribution protocol that uses hybrid encryption to
      convey session keys that are used to encrypt data in IP packets.

      (C) SKIP uses the Diffie-Hellman algorithm (or could use another
      key agreement algorithm) to generate a key-encrypting key for use
      between two entities. A session key is used with a symmetric
      algorithm to encrypt data in one or more IP packets that are to be
      sent from one of the entities to the other. The KEK is used with a
      symmetric algorithm to encrypt the session key, and the encrypted
      session key is placed in a SKIP header that is added to each IP
      packet that is encrypted with that session key.

   $ Simple Mail Transfer Protocol (SMTP)
      (I) A TCP-based, application-level, Internet Standard protocol for
      moving electronic mail messages from one computer to another.
      [R0821].




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   $ Simple Network Management Protocol (SNMP)
      (I) A TCP-based, application-level, Internet Standard protocol for
      conveying management information between managers and agents.
      [R2570, R2574].

   $ simple security property
      See: (secondary definition in) Bell-LaPadula Model.

   $ single sign-on
      (I) A system that enables a user to access multiple computer
      platforms (usually a set of hosts on the same network) or
      application systems after being authenticated just one time. (See:
      Kerberos.)

   (C) Typically, a user logs in just once, and then is transparently
      granted access to a variety of permitted resources with no further
      login being required until after the user logs out. Such a system
      has the advantages of being user friendly and enabling
      authentication to be managed consistently across an entire
      enterprise, and has the disadvantage of requiring all hosts to
      trust the same authentication mechanism.

   $ signature certificate
      (I) A public-key certificate that contains a public key that is
      intended to be used for verifying digital signatures, rather than
      for encrypting data or performing other cryptographic functions.

      (C) A v3 X.509 public-key certificate may have a "keyUsage"
      extension which indicates the purpose for which the certified
      public key is intended.

   $ situation
      See: security situation.

   $ S/Key
      (I) A system that uses a cryptographic hash function to generate a
      sequence of 64-bit, one-time passwords for remote user login.
      [R1760].

      (C) The client generates a one-time password by applying MD4, a
      cryptographic hash function, to the user's secret key multiple
      times. For each successive authentication of the user, the number
      of hash applications is reduced by one. (Thus, an intruder using
      wiretapping cannot compute a valid password from knowledge of one
      previously used.) The server verifies a password by hashing the
      currently presented password (or initialization value) one time
      and comparing the hash result with the previously presented
      password.

   $ SKIP
      See: Simple Key-management for IP.



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   $ SKIPJACK
      (O) A Type II block cipher with a block size of 64 bits and a key
      size of 80 bits, that was developed by NSA and formerly classified
      at the "Secret" level. (See: CAPSTONE, CLIPPER, FORTEZZA, Key
      Exchange Algorithm.)

      (C) On 23 June 1998, NSA announced that SKIPJACK had been
      declassified.

   $ slot
      (O) MISSI usage: One of the FORTEZZA PC card storage areas that
      are each able to hold an X.509 certificate and additional data
      that is associated with the certificate, such as the matching
      private key.

   $ smart card
      (I) A credit-card sized device containing one or more integrated
      circuit chips, which perform the functions of a computer's
      microprocessor, memory, and input/output interface. (See: PC
      card.)

      (C) Sometimes this term is used rather strictly to mean a card
      that closely conforms to the dimensions and appearance of the kind
      of plastic credit card issued by banks and merchants. At other
      times, the term is used loosely to include cards that are large,
      especially cards that are much thicker, such as PC cards.

      (C) A "smart token" is a device that conforms to the definition of
      smart card, except that it is not have standard credit dimensions,
      but is packaged in some other form convenient to be carried on
      one's person, such as a dog tag or door key shape.

   $ smart token
      See: (secondary definition in) smart card.

   $ SMI
      See: security management infrastructure.

   $ S/MIME
      See: Secure/MIME.

   $ SMTP
      See: Simple Mail Transfer Protocol.

   $ smurf
      (I) Software that mounts a denial-of-service attack ("smurfing")
      by exploiting IP broadcast addressing and ICMP ping packets to
      cause flooding. (See: flood, ICMP flood.)

      (D) ISPDs SHOULD NOT use this term because it is not listed in
      most dictionaries and might confuse international readers.



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      (C) A smurf program builds a network packet that appears to
      originate from another address, that of the "victim", either a
      host or an IP router. The packet contains an ICMP ping message
      that is addressed to an IP broadcast address, i.e., to all IP
      addresses in a given network. The echo responses to the ping
      message return to the victim's address. The goal of smurfing may
      be either to deny service at a particular host or to flood all or
      part of an IP network.

   $ sniffing
      (C) A synonym for "passive wiretapping". (See: password sniffing.)

      (D) ISPDs SHOULD NOT use this term because it unnecessarily
      duplicates the meaning of a term that is better established. (See:
      (usage note under) Green Book.

   $ SNMP
      See: Simple Network Management Protocol.

   $ social engineering
      (I) A euphemism for non-technical or low-technology means--such as
      lies, impersonation, tricks, bribes, blackmail, and threats--used
      to attack information systems. (See: masquerade attack.)

      (D) ISPDs SHOULD NOT use this term because it is vague; instead,
      use a term that is specific with regard to the means of attack.

   $ SOCKS
      (I) A protocol [R1928] that provides a generalized proxy server
      that enables client-server applications--such as TELNET, FTP, and
      HTTP; running over either TCP or UDP--to use the services of a
      firewall.

      (C) SOCKS is layered under the application layer and above the
      transport layer. When a client inside a firewall wishes to
      establish a connection to an object that is reachable only through
      the firewall, it uses TCP to connect to the SOCKS server,
      negotiates with the server for the authentication method to be
      used, authenticates with the chosen method, then sends a relay
      request. The SOCKS server evaluates the request, typically based
      on source and destination addresses, and either establishes the
      appropriate connection or denies it.

   $ soft TEMPEST
      (O) The use of software techniques to reduce the radio frequency
      information leakage from computer displays and keyboards. [Kuhn]
      (See: TEMPEST.)

   $ software
      (I) Computer programs (which are stored in and executed by
      computer hardware) and associated data (which is stored in the
      hardware) that may be dynamically written or modified during


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      execution. (Compare with: firmware, hardware.)

   $ SORA
      See: SSO-PIN ORA.

   $ source integrity
      (I) The degree of confidence that can be placed in information
      based on the trustworthiness of its sources. (See: integrity.)

   $ SP3
      See: Security Protocol 3.

   $ SP4
      See: Security Protocol 4.

   $ spam
      (I) (1.) Verb: To indiscriminately send unsolicited, unwanted,
      irrelevant, or inappropriate messages, especially commercial
      advertising in mass quantities. (2.) Noun: electronic "junk mail".
      [R2635]

      (D) This term SHOULD NOT be written in upper-case letters, because
      SPAM(trademark) is a trademark of Hormel Foods Corporation. Hormel
      says, "We do not object to use of this slang term [spam] to
      describe [unsolicited commercial email (UCE)], although we do
      object to the use of our product image in association with that
      term. Also, if the term is to be used, it should be used in all
      lower-case letters to distinguish it from our trademark SPAM,
      which should be used with all uppercase letters."

      (C) In sufficient volume, spam can cause denial of service. (See:
      flooding.) According to the SPAM Web site, the term was adopted as
      a result of the Monty Python skit in which a group of Vikings sang
      a chorus of 'SPAM, SPAM, SPAM . . .' in an increasing crescendo,
      drowning out other conversation. Hence, the analogy applied
      because UCE was drowning out normal discourse on the Internet.

   $ SPC
      See: software publisher certificate.

   $ SPI
      See: Security Parameters Index.

   $ split key
      (I) A cryptographic key that is divided into two or more separate
      data items that individually convey no knowledge of the whole key
      that results from combining the items. (See: dual control, split
      knowledge.)

   $ split knowledge
      (I) A security technique in which two or more entities separately
      hold data items that individually convey no knowledge of the


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      information that results from combining the items. (See: dual
      control, split key.)

      (O) "A condition under which two or more entities separately have
      key components which individually convey no knowledge of the
      plaintext key which will be produced when the key components are
      combined in the cryptographic module." [FP140]

   $ spoofing attack
      (I) A synonym for "masquerade attack".

   $ SSH
      (I) A protocol for secure remote login and other secure network
      services over an insecure network.

      (C) Consists of three major components:

       - Transport layer protocol provides server authentication,
         confidentiality, and integrity. It may optionally also provide
         compression. The transport layer will typically be run over a
         TCP/IP connection, but might also be used on top of any other
         reliable data stream.

       - User authentication protocol authenticates the client-side user
         to the server. It runs over the transport layer protocol.

       - Connection protocol multiplexes the encrypted tunnel into
         several logical channels. It runs over the user authentication
         protocol.

   $ SSL
      See: Secure Sockets Layer, Standard Security Label.

   $ SSO
      See: system security officer.

   $ SSO PIN
      (O) MISSI usage: One of two personal identification numbers that
      control access to the functions and stored data of a FORTEZZA PC
      card. Knowledge of the SSO PIN enables the card user to perform
      the FORTEZZA functions intended for use by an end user and also
      the functions intended for use by a MISSI certification authority.
      (See: user PIN.)

   $ SSO-PIN ORA (SORA)
      (O) MISSI usage: A MISSI organizational RA that operates in a mode
      in which the ORA performs all card management functions and,
      therefore, requires knowledge of the SSO PIN for an end user's
      FORTEZZA PC card.

   $ Standards for Interoperable LAN/MAN Security (SILS)
      (N) (1.) The IEEE 802.10 standards committee. (2.) A developing


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      set of IEEE standards, which has eight parts: (a) Model, including
      security management, (b) Secure Data Exchange protocol, (c) Key
      Management, (d) [has been incorporated in (a)], (e) SDE Over
      Ethernet 2.0, (f) SDE Sublayer Management, (g) SDE Security
      Labels, and (h) SDE PICS Conformance. Parts b, e, f, g, and h are
      incorporated in IEEE Standard 802.10-1998.

   $ star property
      (I) See: "confinement property" under Bell-LaPadula Model.

   $ Star Trek attack
      (C) An attack that penetrates your system where no attack has ever
      gone before.

   $ steganography
      (I) Methods of hiding the existence of a message or other data.
      This is different than cryptography, which hides the meaning in a
      message but does not hide the message itself. (See: cryptology.)

      (C) An example of a steganographic method is "invisible" ink.
      (See: digital watermark.)

   $ storage channel
      See: (secondary definition in) covert channel.

   $ stream cipher
      (I) An encryption algorithm that breaks plaintext into a stream of
      successive bits (or characters) and encrypts the n-th plaintext
      bit with the n-th element of a parallel key stream, thus
      converting the plaintext bit stream into a ciphertext bit stream.
      [Schn] (Compare with: block cipher.)

   $ strong authentication
      (I) An authentication process that uses cryptography--particularly
      public-key certificates--to verify the identity claimed for an
      entity. (See: X.509.)

      (O) "Authentication by means of cryptographically derived
      credentials." [X509]

   $ subject
      1. (I) In a computer system: A system entity that causes
      information to flow among objects or changes the system state;
      technically, a process-domain pair. (See: Bell-LaPadula Model.)

      2. (I) Of a certificate: The entity name that is bound to the data
      items in a digital certificate, and particularly a name that is
      bound to a key value in a public-key certificate.

   $ subnetwork
      (N) An OSI term for a system of packet relays and connecting links
      that implement the lower three protocol layers of the OSIRM to


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      provide a communication service that interconnects attached end
      systems. Usually the switches operate at OSI layer 3 and are all
      of the same type (e.g., all X.25 packet switches, or all interface
      units in an IEEE 802.3 LAN). (See: gateway, internet, router.)

   $ subordinate certification authority (SCA)
      (I) A CA whose public-key certificate is issued by another
      (superior) CA.

      (O) MISSI usage: The fourth-highest (bottom) level of a MISSI
      certification hierarchy; a MISSI certification authority whose
      public-key certificate is signed by a MISSI CA rather than by a
      MISSI PCA. A MISSI SCA is the administrative authority for a
      subunit of an organization, established when it is desirable to
      organizationally distribute or decentralize the CA service. The
      term refers both to that authoritative office or role, and to the
      person who fills that office A MISSI SCA registers end users and
      issues their certificates and may also register ORAs, but may not
      register other CAs. An SCA periodically issues a CRL.

   $ subordinate distinguished name
      (I) An X.500 DN is subordinate to another if it begins with a set
      of attributes that is the same as the entire second DN except for
      the terminal attribute of the second DN (which is usually the name
      of a CA). For example, the DN <C=FooLand, O=Gov, OU=Treasurer,
      CN=DukePinchpenny> is subordinate to the DN <C=FooLand, O=Gov,
      CN=KingFooCA>.

   $ superencryption
      (I) An encryption operation for which the plaintext input to be
      transformed is the ciphertext output of a previous encryption
      operation.

   $ survivability
      (I) The ability of a system to remain in operation or existence
      despite adverse conditions, including both natural occurrences,
      accidental actions, and attacks on the system. (See: availability,
      reliability.)

   $ symmetric cryptography
      (I) A branch of cryptography involving algorithms that use the
      same key for two different steps of the algorithm (such as
      encryption and decryption, or signature creation and signature
      verification).

      (C) Symmetric cryptography has been used for thousands of years
      [Kahn]. A modern example of is the U.S. Government's Data
      Encryption Standard. Symmetric cryptography is sometimes called
      "secret-key cryptography" (also see: public-key cryptography)
      because the entities that share the key, such as the originator
      and the recipient of a message, need to keep the key secret. For
      example, when Alice wants to ensure confidentiality for data she


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      sends to Bob, she encrypts the data with a secret key, and Bob
      uses the same key to decrypt. Keeping the shared key secret
      entails both cost and risk when the key is distributed to both
      Alice and Bob. Thus, symmetric cryptography has a key management
      disadvantage compared to asymmetric cryptography. (See: key
      agreement.)

   $ symmetric key
      (I) A cryptographic key that is used in a symmetric cryptographic
      algorithm.

   $ SYN flood
      (I) A denial of service attack that sends a host more TCP SYN
      packets (request to synchronize sequence numbers, used when
      opening a connection) than the protocol implementation can handle.
      (See: flooding.)

   $ system
      (C) In this Glossary, the term is mainly used as an abbreviation
      for "automated information system".

   $ system entity
      (I) An active element of a system--an automated process, a
      subsystem, a person or group of persons--that incorporates some
      specific set of capabilities.

   $ system high
      (I) The highest security level supported by a system at a
      particular time or in a particular environment.

   $ system high security mode
      (I) A mode of operation of an information system, wherein all
      users having access to the system possess a security clearance or
      authorization, but not necessarily a need-to-know, for all data
      handled by the system.

      (C) This mode is defined formally in U.S. Department of Defense
      policy regarding system accreditation [DOD2], but the term is
      widely used outside the Defense Department and outside the
      Government.

   $ system integrity
      (I) "The quality that a system has when it can perform its
      intended function in a unimpaired manner, free from deliberate or
      inadvertent unauthorized manipulation." [NCS04] (See: system
      integrity service.)

   $ system integrity service
      (I) A security service that protects system resources in a
      verifiable manner against unauthorized or accidental change, loss,
      or destruction. (See: system integrity.)



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   $ system low
      (I) The lowest security level supported by a system at a
      particular time or in a particular environment.

   $ system resource
      (I) Data contained in an information system; or a service provided
      by a system; or a system capability, such as processing power or
      communication bandwidth; or an item of system equipment (i.e., a
      system component--hardware, firmware, software, or documentation);
      or a facility that houses system operations and equipment.

   $ system verification
      See: (secondary definition in) verification.

   $ TACACS
   $ TACACS+
      See: Terminal Access Controller (TAC) Access Control System.

   $ tamper
      (I) Make an unauthorized modification in a system that alters the
      system's functioning in a way that degrades the security services
      that the system was intended to provide.

   $ TCB
      See: trusted computing base.

   $ TCP
      See: Transmission Control Protocol.

   $ TCP/IP
      (I) A synonym for "Internet Protocol Suite", in which the
      Transmission Control Protocol (TCP) and the Internet Protocol (IP)
      are important parts.

   $ TCSEC
      See: Trusted Computer System Evaluation Criteria.

   $ TELNET
      (I) A TCP-based, application-level, Internet Standard protocol for
      remote login from one host to another. [R0854]

   $ TEMPEST
      (O) A nickname for specifications and standards for limiting the
      strength of electromagnetic emanations from electrical and
      electronic equipment and thus reducing vulnerability to
      eavesdropping. This term originated in the U.S. Department of
      Defense. (See: emanation security, soft tempest.)

      (D) ISPDs SHOULD NOT use this term as a synonym for
      "electromagnetic emanations security".




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   $ Terminal Access Controller (TAC) Access Control System (TACACS)
      (I) A UDP-based authentication and access control protocol [R1492]
      in which a network access server receives an identifier and
      password from a remote terminal and passes them to a separate
      authentication server for verification. Originally developed for
      ARPANET and now evolved for use in commercial equipment:

       - "XTACACS": The name of Cisco Corporation's implementation,
         which enhances and extends the original TACACS.

       - "TACACS+": A TCP-based protocol that improves on TACACS and
         XTACACS by separating the functions of authentication,
         authorization, and accounting and by encrypting all traffic
         between the network access server and authentication server. It
         is extensible to allow any authentication mechanism to be used
         with TACACS+ clients.

      (C) TACACS can provide service not only for network access servers
      but also routers and other networked computing devices via one or
      more centralized authentication servers.

   $ TESS
      See: The Exponential Encryption System.

   $ The Exponential Encryption System (TESS)
      (I) A system of separate by cooperation cryptographic mechanisms
      and functions for the secure authenticated exchange of
      cryptographic keys, the generation of digital signatures, and the
      distribution of public keys. TESS employs asymmetric cryptography,
      based on discrete exponentiation, and a structure of self-
      certified public keys. [R1824]

   $ threat
      (I) A potential for violation of security, which exists when there
      is a circumstance, capability, action, or event that could breach
      security and cause harm. (See: attack, threat action, threat
      consequence.)

      (C) That is, a threat is a possible danger that might exploit a
      vulnerability. A threat can be either "intentional" (i.e.,
      intelligent; e.g., an individual cracker or a criminal
      organization) or "accidental" (e.g., the possibility of a computer
      malfunctioning, or the possibility of an "act of God" such as an
      earthquake, a fire, or a tornado).

      (C) In some contexts, the term is used narrowly to refer only to
      intelligent threats; for example:

      (N) U. S. Government usage: The technical and operational
      capability of a hostile entity to detect, exploit, or subvert
      friendly information systems and the demonstrated, presumed, or
      inferred intent of that entity to conduct such activity.


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   $ threat action
      (I) An assault on system security. (See: attack, threat, threat
      consequence.)

      (C) A complete security architecture deals with both intentional
      acts (i.e. attacks) and accidental events [FIPS31]. Various kinds
      of threat actions are defined as subentries under "threat
      consequence".

   $ threat analysis
      (I) An analysis of the probability of occurrences and consequences
      of damaging actions to a system.

   $ threat consequence
      (I) A security violation that results from a threat action.
      Includes disclosure, deception, disruption, and usurpation. (See:
      attack, threat, threat action.)

      (C) The following subentries describe four kinds of threat
      consequences, and also list and describe the kinds of threat
      actions that cause each consequence. Threat actions that are
      accidental events are marked by "*".

      1. "(Unauthorized) Disclosure" (a threat consequence): A
         circumstance or event whereby an entity gains access to data
         for which the entity is not authorized. (See: data
         confidentiality.) The following threat actions can cause
         unauthorized disclosure:

         A. "Exposure": A threat action whereby sensitive data is
            directly released to an unauthorized entity. This includes:

            a. "Deliberate Exposure: Intentional release of sensitive
               data to an unauthorized entity.

            b. "Scavenging": Searching through data residue in a system
               to gain unauthorized knowledge of sensitive data.

            c* "Human error": Human action or inaction that
               unintentionally results in an entity gaining unauthorized
               knowledge of sensitive data.

            d* "Hardware/software error". System failure that results in
               an entity gaining unauthorized knowledge of sensitive
               data.

         B. "Interception": A threat action whereby an unauthorized
            entity directly accesses sensitive data traveling between
            authorized sources and destinations. This includes:

            a. "Theft": Gaining access to sensitive data by stealing a


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               shipment of a physical medium, such as a magnetic tape or
               disk, that holds the data.

            b. "Wiretapping (passive): Monitoring and recording data
               that is flowing between two points in a communication
               system. (See: wiretapping.)

            c. "Emanations analysis": Gaining direct knowledge of
               communicated data by monitoring and resolving a signal
               that is emitted by a system and that contains the data
               but is not intended to communicate the data. (See:
               emanation.)

         C. "Inference": A threat action whereby an unauthorized entity
            indirectly accesses sensitive data (but not necessarily the
            data contained in the communication) by reasoning from
            characteristics or byproducts of communications. This
            includes:

            a. Traffic analysis: Gaining knowledge of data by observing
               the characteristics of communications that carry the
               data. (See: (main Glossary entry for) traffic analysis.)

            b. "Signals analysis": Gaining indirect knowledge of
               communicated data by monitoring and analyzing a signal
               that is emitted by a system and that contains the data
               but is not intended to communicate the data. (See:
               emanation.)

         D. "Intrusion": A threat action whereby an unauthorized entity
            gains access to sensitive data by circumventing a system's
            security protections. This includes:

            a. "Trespass": Gaining unauthorized physical access to
               sensitive data by circumventing a system's protections.

            b. "Penetration": Gaining unauthorized logical access to
               sensitive data by circumventing a system's protections.

            c. "Reverse engineering": Acquiring sensitive data by
               disassembling, and analyzing the design, of a system
               component.

            d. Cryptanalysis: Transforming encrypted data into plaintext
               without having prior knowledge of variables or algorithms
               used in the encipherment process. (See: (main Glossary
               entry for) cryptanalysis.)

      2. "Deception" (a threat consequence): A circumstance or event
         that may result in an authorized entity receiving false data
         and believing it to be true. The following threat actions can
         cause deception:


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         A. "Masquerade": A threat action whereby an unauthorized entity
            gains access to a system or performs a malicious act by
            posing as an authorized entity.(See: (main Glossary entry
            for) masquerade attack.)

            a. "Spoof": Attempt by an unauthorized entity to gain access
               to a system by posing as an authorized user.

            b. "Malicious logic": In context of masquerade, any
               hardware, firmware, or software (e.g., Trojan horse) that
               appears to perform a useful or desirable function, but
               actually gains unauthorized access to system resources or
               tricks a user into executing other malicious logic. (See:
               (main Glossary entry for) malicious logic.)

         B. "Falsification": A threat action whereby false data deceives
            an authorized entity. (See: active wiretapping.)

            a. "Substitution": Altering or replacing valid data with
               false data that serves to deceive an authorized entity.

            b. "Insertion": Introducing or adding valid data with false
               data that serves to deceive an authorized entity.

         C. "Repudiation": Action whereby an entity deceives another by
            falsely denying responsibility for an act. (See: non-
            repudiation service, (main Glossary entry for) repudiation.)

            a. "False denial of origin": A threat action whereby the
               originator of data denies responsibility for its
               generation.

            b. "False denial of receipt": A threat action whereby the
               recipient of data denies receiving and possessing the
               data.

      3. "Disruption" (a threat consequence): A circumstance or event
         that interrupts or prevents the correct operation of system
         services and functions. (See: denial of service.) The following
         threat actions that can cause disruption:

         A. "Incapacitation": A threat action that prevents or
            interrupts system operation by disabling a system component.

            a. "Malicious logic": In context of incapacitation, any
               hardware, firmware, or software (e.g., logic bomb)
               intentionally introduced into a system to destroy system
               functions or resources. (See: (main Glossary entry for)
               malicious logic.)

            b. "Physical destruction": Deliberate destruction of a


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               system component to interrupt or prevent system
               operation.

            c* "Human error": Action or inaction that disables a system
               component.

            d* "Hardware or software error": Error that causes failure
               of a system component and leads to disruption of system
               operation.

            e* "Natural disaster": Any "act of God" (e.g., fire, flood,
               earthquake, lightning, or wind) that disables a system
               component. [FP031 section 2]

         B. "Corruption": A threat action that undesirably alters system
            operation by adversely modifying system functions or data.

            a. "Tamper": In context of corruption, deliberate alteration
               of a system's logic, data, or control information to
               interrupt or prevent correct operation of system
               functions.

            b. "Malicious logic": In context of corruption, any
               hardware, firmware, or software (e.g., a computer virus)
               intentionally introduced into a system to modify system
               functions or data. (See: (main Glossary entry for)
               malicious logic.)

            c* "Human error": Human action or inaction that results in
               the alteration of system functions or data.

            d* "Hardware or software error": Error that results in the
               alteration of system functions or data.

            e* "Natural disaster": Any "act of God" (e.g., power surge
               caused by lightning) that alters system functions or
               data. [FP031 section 2]

         C. "Obstruction": A threat action that interrupts delivery of
            system services by hindering system operations.

            a. "Interference": Disruption of system operations by
               blocking communications or user data or control
               information.

            b. "Overload": Hindrance of system operation by placing
               excess burden on the performance capabilities of a system
               component. (See: flooding.)

      4. "Usurpation" (a threat consequence): A circumstance or event
         that results in control of system services or functions by an
         unauthorized entity. The following threat actions can cause


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         usurpation:

         A. "Misappropriation": A threat action whereby an entity
            assumes unauthorized logical or physical control of a system
            resource.

            a. "Theft of service": Unauthorized use of service by an
               entity.

            b. "Theft of functionality": Unauthorized acquisition of
               actual hardware, software, or firmware of a system
               component.

            c. "Theft of data": Unauthorized acquisition and use of
               data.

         B. "Misuse": A threat action that causes a system component to
            perform a function or service that is detrimental to system
            security.

            a. "Tamper": In context of misuse, deliberate alteration of
               a system's logic, data, or control information to cause
               the system to perform unauthorized functions or services.

            b. "Malicious logic": In context of misuse, any hardware,
               software, or firmware intentionally introduced into a
               system to perform or control execution of an unauthorized
               function or service.

            c. "Violation of permissions": Action by an entity that
               exceeds the entity's system privileges by executing an
               unauthorized function.

   $ thumbprint
      (I) A pattern of curves formed by the ridges on the tip of a
      thumb. (See: biometric authentication, fingerprint.)

      (D) ISPDs SHOULD NOT use this term as a synonym for "hash result"
      because that meaning concepts in a potentially misleading way.

   $ ticket
      (I) A synonym for "capability".

      (C) A ticket is usually granted by a centralized access control
      server (ticket-granting agent) to authorize access to a system
      resource for a limited time. Tickets have been implemented with
      symmetric cryptography (see: Kerberos), but can also be
      implemented as attribute certificates using asymmetric
      cryptography. In effect, an RA that does not issue digital
      certificates itself, but vouches for the identity of prospective
      certificate holders to a CA, is a ticket-granting agent. [FPKI]



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   $ timing channel
      See: (secondary definition in) covert channel.

   $ TLS
      See: Transport Layer Security. (See: TLSP.)

   $ TLSP
      See: Transport Layer Security Protocol. (See: TLS.)

   $ token
      1. (I) General usage: An object that is used to control access and
      is passed between cooperating entities in a protocol that
      synchronizes use of a shared resource. Usually, the entity that
      currently holds the token has exclusive access to the resource.

      2. (I) Authentication usage: A data object or a portable, user-
      controlled, physical device used to verify an identity in an
      authentication process. (See: authentication information, dongle.)

      3. (I) Cryptographic usage: See: cryptographic token.

   $ token backup
      (I) A token management operation that stores sufficient
      information in a database (e.g., in a CAW) to recreate or restore
      a security token (e.g., a smart card) if it is lost or damaged.

   $ token copy
      (I) A token management operation that copies all the personality
      information from one security token to another. However, unlike in
      card restore, the second card is initialized with its own,
      different local security values such as PINs and card storage
      keys.

   $ token management
      (I) The process of initializing security tokens (e.g., see: smart
      card), loading data into the tokens, and controlling the tokens
      during their life cycle. May include performing key management and
      certificate management functions; generating and installing PINs;
      loading user personality data; performing card backup, card copy,
      and card restore operations; and updating firmware.

   $ token restore
      (I) A token management operation that loads a token with data for
      the purpose of recreating (duplicating) the contents previously
      held by that or another token.

   $ token storage key
      (I) A cryptography key used to protect data that is stored on a
      security token.

   $ top CA
      (I) A CA that is the highest level (i.e., is the most trusted CA)


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      in a certification hierarchy. (See: root.)

   $ top-level specification
      (I) "A non-procedural description of system behavior at the most
      abstract level; typically a functional specification that omits
      all implementation details." [NCS04] (See: (discussion under)
      security policy.)

      (C) A top-level specification may be descriptive or formal:

       - "Descriptive top-level specification": One that is written in a
      natural language like English or an informal design notation.

       - "Formal top-level specification": One that is written in a
      formal mathematical language to allow theorems to be proven
      showing that the specification correctly implements a set of
      formal requirements or a formal security model. (See: correctness
      proof.)

   $ traffic analysis
      (I) Inference of information from observable characteristics of
      data flow(s), even when the data is encrypted or otherwise not
      directly available. Such characteristics include the identities
      and locations of the source(s) and destination(s), and the
      presence, amount, frequency, and duration of occurrence. (See:
      wiretapping.)

      (O) "The inference of information from observation of traffic
      flows (presence, absence, amount, direction, and frequency)."
      [I7498 Part 2]

   $ traffic flow confidentiality
      (I) A data confidentiality service to protect against traffic
      analysis.

      (O) "A confidentiality service to protect against traffic
      analysis." [I7498 Part 2]

   $ traffic padding
      (I) "The generation of spurious instances of communication,
      spurious data units, and/or spurious data within data units."
      [I7498 Part 2]

   $ tranquillity property
      See: (secondary definition in) Bell-LaPadula Model.

   $ Transmission Control Protocol (TCP)
      (I) An Internet Standard protocol [R0793] that reliably delivers a
      sequence of datagrams (discrete sets of bits) from one computer to
      another in a computer network.

      (C) TCP is designed to fit into a layered hierarchy of protocols


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      that support internetwork applications. TCP assumes it can obtain
      a simple, potentially unreliable datagram service (such as the
      Internet Protocol) from the lower level protocols.

   $ Transport Layer Security (TLS)
      (I) TLS Version 1.0 is an Internet protocol based-on and very
      similar to SSL Version 3.0. (Compare with: TLSP.)

      (C) The TLS protocol is misnamed, because it operates well above
      OSI layer 4.

   $ Transport Layer Security Protocol (TLSP)
      (I) An end-to-end encryption (ISO 10736) protocol that provides
      security services at the bottom of OSI layer 4, i.e., directly
      above OSI layer 3. (Compare with: TLS.)

      (C) TLSP evolved directly from the SP4 protocol of SDNS.

   $ transport mode vs. tunnel mode
      (I) IPsec usage: Two ways to apply IPsec protocols (AH and ESP) to
      protect communications:

       - "Transport mode": The protection applies mainly to the packets
         of upper layer protocols, the ones that are carried above IP.

       - "Tunnel mode": The protection applies to tunneled IP packets.

      (C) A transport mode security association is always between two
      hosts. A tunnel mode security association is one that is applied
      to an IP tunnel, but the each end may be either a host or a
      gateway; and, whenever either end of a security association is a
      security gateway, the association is required to be in tunnel
      mode.

   $ trap door
      (I) A hidden computer flaw known to an intruder, or hidden
      computer mechanism (usually software) installed by an intruder,
      who can activate the mechanism to gain access to the computer
      without being blocked by security mechanisms. (See: back door,
      Trojan horse.)

   $ triple DES
      (I) An block cipher, based on DES, that transforms each 64-bit
      plaintext block by applying the Data Encryption Algorithm three
      successive times, using either two or three different keys, for an
      key length of 112 or 168 bits. [A9052] (See: DES.)

      (C) IPsec usage: The algorithm variation proposed for ESP uses a
      168-bit key, consisting of three independent 56-bit quantities
      used by the Data Encryption Algorithm, and a 64-bit initialization
      vector. Each datagram contains an IV to ensure that each received
      datagram can be decrypted, even if other datagrams are dropped or


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      datagrams are reordered in transit. [R1851]

   $ triple-wrapped
      (I) S/MIME usage: Data that has been signed with a digital
      signature, and then encrypted, and then signed again. [R2634]

   $ Trojan horse
      (I) A computer program that appears to have a useful function, but
      also has a hidden and potentially malicious function that evades
      security mechanisms, sometimes by exploiting legitimate
      authorizations of a system entity that invokes the program.

   $ trust
      1. (I) Information system usage: The extent to which someone who
      relies on a system can have confidence that the system meets its
      specifications, i.e., that the system does what it claims to do
      and does not perform unwanted functions. (See: trust level.)

      (C) "trusted vs. trustworthy": In discussing a system or system
      process or object, this Glossary (and industry usage) prefers the
      term "trusted" to describe a system that operates as expected,
      according to design and policy. When the trust can also be
      guaranteed in some convincing way, such as through formal analysis
      or code review, the system is termed "trustworthy"; this differs
      from the ABA Guidelines definition (see: trustworthy system).

      2. (I) PKI usage: A relationship between a certificate user and a
      CA in which the user acts according to the assumption that the CA
      creates only valid digital certificates.

      (O) "Generally, an entity can be said to 'trust' a second entity
      when it (the first entity) makes the assumption that the second
      entity will behave exactly as the first entity expects. This trust
      may apply only for some specific function. The key role of trust
      in [X.509] is to describe the relationship between an entity and a
      [certification] authority; an entity shall be certain that it can
      trust the certification authority to create only valid and
      reliable certificates." [X509]

   $ trust chain
      (D) ISPDs SHOULD NOT use this term as a synonym for "certification
      path" because it mixes concepts (see: trust) in a potentially
      misleading way.

   $ trust-file PKI
      (I) A non-hierarchical PKI in which a each certificate user has a
      local file (used by application software) of public-key
      certificates that the user trusts as starting points (see: root)
      for certification paths. (See: hierarchical PKI, mesh PKI, web of
      trust.)

      (C) For example, popular browsers are distributed with an initial


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      file of trusted certificates, which often are self-signed
      certificates. Users can add certificates to the file or delete
      from it. The file may be directly managed by the user, or the
      user's organization may manage it from a centralized server.

   $ trust hierarchy
      (D) ISPDs SHOULD NOT use this term as a synonym for "certification
      hierarchy" because this term mixes concepts (see: trust) in a
      potentially misleading way and duplicates the meaning of another,
      standardized term. (See: web of trust.)

   $ trust level
      (I) A characterization of a standard of security protection to be
      met by a computer system.

      (C) The TCSEC defines eight trust levels. From the lowest to the
      highest, they are D, C1, C2, B1, B2, B3, and A1. A trust level is
      based not only on the presence of security mechanisms but also on
      the use of systems engineering discipline to properly structure
      the system and on implementation analysis to ensure that the
      system provides the appropriate degree of trust.

   $ trusted
      See: (discussion under) trust.

   $ trusted certificate
      (I) A certificate that is trusted a priori by a certificate user,
      such as a public-key certificate that can be used to provide the
      first public key in a certification path.

      (C) A trusted public-key certificate might be the root certificate
      in a hierarchical PKI, or the certificate of the CA that issued
      the user's own certificate in a mesh PKI, or any certificate
      accepted by the user in a trust-file PKI.

   $ trusted computer system
      (I) "A system that employs sufficient hardware and software
      assurance measures to allow its use for simultaneous processing of
      a range of sensitive or classified information." [NCS04] (See:
      (discussion under) trust.)

   $ Trusted Computer System Evaluation Criteria (TCSEC)
      (N) A standard for evaluating the security provided by operating
      systems [CSC001, DOD1]. Informally called the "Orange Book"
      because of the color of its cover; first document in the Rainbow
      Series. (See: (usage note under) Green Book, Orange Book, trust
      level.)

      (C) To be superseded by the Common Criteria.

   $ trusted computing base (TCB)
      (I) "The totality of protection mechanisms within a computer


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      system, including hardware, firmware, and software, the
      combination of which is responsible for enforcing a security
      policy." [NCS04] (See: (discussion of "trusted" under) trust.)

   $ trusted distribution
      (I) "A trusted method for distributing the TCB hardware, software,
      and firmware components, both originals and updates, that provides
      methods for protecting the TCB for modification during
      distribution and for detection of any changes to the TCB that may
      occur." [NCS04]

   $ trusted key
      (I) A public key that is trusted a priori by a user, such as a key
      that can be used as the first public key in a certification path.

      (C) A trusted public key can be (a) the root key in a hierarchical
      PKI, (b) the key of the CA that issued the user's own certificate
      in a mesh PKI, or (c) any key accepted by the user in a trust-file
      PKI.

   $ trusted path
      (I) COMPUSEC usage: A mechanism by which a computer system user
      can communicate directly and reliably with the trusted computing
      base (TCB) and that can only be activated by the user or the TCB
      and cannot be imitated by untrusted software within the computer.
      [NCS04]

      (I) COMSEC usage: A mechanism by which a person or process can
      communicate directly with a cryptographic module and that can only
      be activated by the person, process, or module, and cannot be
      imitated by untrusted software within the module. [FP140]

   $ trusted process
      (I) A system process that has privileges that enable it to affect
      the state of system security and that can, therefore, through
      incorrect or malicious execution, violate the system's security
      policy. (See: privileged process, (discussion of "trusted" under)
      trust.)

   $ trusted subnetwork
      (I) A subnetwork containing hosts and routers that trust each
      other not to engage in active or passive attacks. (There also is
      an assumption that the underlying communication channel--for
      example, a LAN--is not being attacked by other means.)

   $ trusted system
      See: (discussion under) trust, trusted computer system,
      trustworthy system.

   $ Trusted Systems Interoperability Group (TSIG)
      (N) A forum of computer vendors, system integrators, and users
      devoted to promoting interoperability of trusted computer systems.


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      TSIG meetings are open to all persons who are working in the
      INFOSEC area.

   $ trustworthy system
      (O) ABA usage: "Computer hardware, software, and procedures that:
      (a) are reasonably secure from intrusion and misuse; (b) provide a
      reasonably reliable level of availability, reliability, and
      correct operation; (c) are reasonably suited to performing their
      intended functions; and (d) adhere to generally accepted security
      principles." [ABA] This differs somewhat from other industry usage
      (see: (discussion of "trusted vs. trustworthy" under) trust).

   $ TSIG
      See: Trusted System Interoperability Group.

   $ tunnel
      (I) A communication channel created in a computer network by
      encapsulating (carrying, layering; i.e., "tunneling") a
      communication protocol's data packets in (on top of) a second
      protocol that normally would be carried above, or at the same
      layer as, the first one. (See: L2TP, VPN.)

      (C) Tunneling can involve almost any OSI or TCP/IP protocol
      layers; for example, a TCP connection between two hosts could
      conceivably be tunneled through email messages across the
      Internet. Usually, a tunnel is a logical point-to-point link--
      i.e., an OSI layer 2 connection--created by encapsulating the
      layer 2 protocol in a n protocol (such as TCP), or in a OSI layer
      3 internetwork protocol (such as IP), or in another layer 2
      protocol. Often, encapsulation is accomplished with an
      intermediate protocol (a tunneling protocol), such as L2TP,
      layered between the tunneled layer 2 protocol and the
      encapsulating protocol.

      (C) Tunneling can move data between computers that use a protocol
      not supported by the network connecting them. Tunneling also can
      enable a computer network to use the services of a second network
      as though the second network were a set of point-to-point links
      between the first network's nodes. (See: virtual private network.)

      (O) SET usage: The name of a SET private extension that indicates
      whether the CA or the payment gateway supports passing encrypted
      messages to the cardholder through the merchant. If so, the
      extension lists OIDs of symmetric encryption algorithms that are
      supported.

   $ tunnel mode
      (I) IPsec usage: See: transport mode vs. tunnel mode.

   $ two-person control
      (I) The close surveillance and control of a system, process, or
      materials (especially with regard to cryptography) at all times by


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      a minimum of two appropriately authorized persons, each capable of
      detecting incorrect and unauthorized procedures with respect to
      the tasks to be performed and each familiar with established
      security requirements. (See: dual control, no-lone zone.)

   $ Type I cryptography
      (O) A cryptographic algorithm or device approved by the U.S.
      National Security Agency for protecting classified information.

   $ Type II cryptography
      (O) A cryptographic algorithm or device approved by the U.S.
      National Security Agency for protecting sensitive unclassified
      information in systems (as specified in section 2315 of Title 10
      United States Code, or section 3502(2) of Title 44, United States
      Code.)

   $ Type III cryptography
      (O) A cryptographic algorithm or device approved as a Federal
      Information Processing Standard.

   $ UDP
      See: User Datagram Protocol.

   $ unclassified
      (I) Not classified.

   $ unencrypted
      (I) Not encrypted.

   $ unforgeable
      (I) Cryptographic usage: The property of a cryptographic data
      structure (i.e., a data structure that is computed using one more
      cryptographic functions) that makes it computationally infeasible
      to construct (i.e., compute) an unauthorized but correct value of
      the structure without having knowledge of one of more keys. (E.g.,
      see: digital certificate.)

      (C) This definition is narrower than general English usage, in
      which "unforgeable" means unable to be fraudulently created or
      duplicated. In that broader sense, anyone can forge a digital
      certificate containing any set of data items whatsoever by
      generating the to-be-signed certificate and signing it with any
      private key whatsoever. But for PKI purposes, the forged data
      structure is invalid if it is not signed with the true private key
      of the claimed issuer; thus, the forgery will be detected when a
      certificate user uses the true public key of the claimed issuer to
      verify the signature.

   $ uniform resource identifier (URI)
      (I) A type of formatted identifier that encapsulates the name of
      an Internet object, and labels it with an identification of the
      name space, thus producing a member of the universal set of names


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      in registered name spaces and of addresses referring to registered
      protocols or name spaces. [R1630]

      (C) URIs are used in HTML to identify the target of hyperlinks. in
      common practice, URIs include uniform resource locators [R2368]
      and relative URLs. [R1808].

   $ uniform resource locator (URL)
      (I) A type of formatted identifier that describes the access
      method and location of an information resource object on the
      Internet. [R1738]

      (C) A URL is a URI that provides explicit instructions on how to
      access the named object. For example,
      "ftp://bbnarchive.bbn.com/foo/bar/picture/cambridge.zip" is a URL.
      The part before the colon specifies the access scheme or protocol,
      and the part after the colon is interpreted according to that
      access method. Usually, two slashes after the colon indicate the
      host name of a server (written as a domain name). In an FTP or
      HTTP URL, the host name is followed by a path name of a file on
      the server. The last (optional) part of a URL may be either a
      fragment identifier that indicates a position in the file, or a
      query string.

   $ uniform resource name (URN)
      (I) A URI that has an institutional commitment to persistence and
      availability.

   $ untrusted process
      (I) A system process that is not able to affect the state of
      system security through incorrect or malicious operation, usually
      because its operation is confined by a security kernel. (See:
      trusted process.)

   $ UORA
      See: user-PIN ORA.

   $ update
      See: certificate update and key update.

   $ URI
      See: uniform resource identifier.

   $ URL
      See: uniform resource locator.

   $ URN
      See: uniform resource name.

   $ user
      (I) A person (or organization entity) or an automated process
      (usually acting on behalf of a person) that accesses a system,


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      whether authorized to do so or not.

      (C) Because this term can be understood in many ways, any ISPD
      that uses it SHOULD provide an explicit definition. [R2504]

   $ User Datagram Protocol (UDP)
      (I) An Internet Standard [R0768] protocol that provides a datagram
      mode of packet-switched computer communication in an internetwork.

      (C) UDP assumes that IP is the underlying protocol. UDP enables
      application programs to send transaction-oriented data to other
      programs with minimal protocol mechanism. UDP does not provide
      reliable delivery, flow control, sequencing, or other end-to-end
      services that TCP provides.

   $ user identifier
      (I) A character string or symbol that is used in a system to
      uniquely name a specific user or group of users.

      (C) Often verified by a password in an authentication process.

   $ user PIN
      (O) MISSI usage: One of two personal identification numbers that
      control access to the functions and stored data of a FORTEZZA PC
      card. Knowledge of the user PIN enables the card user to perform
      the FORTEZZA functions that are intended for use by an end user.
      (See: SSO PIN.)

   $ user-PIN ORA (UORA)
      (O) A MISSI organizational RA that operates in a mode in which the
      ORA performs only the subset of card management functions that are
      possible with knowledge of the user PIN for a FORTEZZA PC card.
      (See: no-PIN ORA, SSO-PIN ORA.)

   $ usurpation
      See: (secondary definition in) threat consequence.

   $ UTCTime
      (N) The ASN.1 data type "UTCTime" contains a calendar date
      (YYMMDD) and a time to a precision of either one minute (HHMM) or
      one second (HHMMSS), where the time is either (a) Coordinated
      Universal Time or (b) the local time followed by an offset that
      enables Coordinated Universal Time to be calculated. Note: UTCTime
      has the Year 2000 problem. (See: Coordinated Universal Time,
      GeneralizedTime.)

   $ v1 certificate
      (C) Ambiguously refers to either an X.509 public-key certificate
      in its version 1 format, or an X.509 attribute certificate in its
      version 1 format. However, many people who use this term are not
      aware that X.509 specifies attribute certificates that do not
      contain a public key. ISPDs MAY use this term as an abbreviation


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      for "version 1 X.509 public-key certificate", but only after using
      the full term at the first instance.

      (D) ISPDs SHOULD NOT use this term as an abbreviation to mean
      "version 1 X.509 attribute certificate".

   $ v1 CRL
      (I) A synonym for and "X.509 CRL" in version 1 format.

   $ v2 certificate
      (I) A synonym for an "X.509 public-key certificate" in version 2
      format.

   $ v2 CRL
      (I) A synonym for an "X.509 CRL" in version 2 format.

   $ v3 certificate
      (I) A synonym for an "X.509 public-key certificate" in version 3
      format.

   $ valid certificate
      (I) A digital certificate for which the binding of the data items
      can be trusted; one that can be validated successfully. (See:
      validate vs. verify.)

   $ valid signature
      (D) ISPDs SHOULD NOT use this term; instead, use "authentic
      signature". This Glossary recommends saying "validate the
      certificate" and "verify the signature" (see: validate vs.
      verify); therefore, it would be inconsistent to say that a
      signature is "valid".

   $ validate vs. verify
      (C) The PKI community uses words inconsistently when describing
      what a certificate user does to make certain that a digital
      certificate can be trusted. Usually, we say "verify the signature"
      but say "validate the certificate"; i.e., we "verify" atomic
      truths but "validate" data structures, relationships, and systems
      that are composed of or depend on verified items. Too often,
      however, verify and validate are used interchangeably.

      ISPDs SHOULD follow the following two rules to ensure consistency
      and align Internet security terminology with ordinary English:

       - Rule 1: Use "validate" when referring to a process intended to
         establish the soundness or correctness of a construct, like a
         public-key certificate or a certification path.

       - Rule 2: Use "verify" when referring to a process intended to
         test or prove the truth or accuracy of a fact or value.

      The rationale for Rule 1 is that "valid" derives from a word that


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      means "strong" in Latin. Thus, to validate means to make sure that
      a construction is sound. A certificate user validates a public-key
      certificate to establish trust in the binding that the certificate
      asserts between an identity and a key. (To validate can also mean
      to officially approve something; thus NIST validates cryptographic
      modules for conformance with FIPS PUB 140-1.)

      The rationale for Rule 2 is that "verify" derives from a word that
      means "true" in Latin. Thus, to verify means to prove the truth of
      an assertion by examining evidence or performing tests. To verify
      an identity, an authentication process examines identification
      information that is presented or generated. To validate a
      certificate, a certificate user verifies the digital signature on
      the certificate by performing calculations; verifies that the
      current time is within the certificate's validity period; and may
      need to validate a certification path involving additional
      certificates.

   $ validation
      See: validate vs. verify.

   $ validity period
      (I) A data item in a digital certificate that specifies the time
      period for which the binding between data items (especially
      between the subject name and the public key value in a public-key
      certificate) is valid, except if the certificate appears on a CRL
      or the key appears on a CKL.

   $ value-added network (VAN)
      (I) A computer network or subnetwork (which is usually a
      commercial enterprise) that transmits, receives, and stores EDI
      transactions on behalf of its customers.

      (C) A VAN may also provide additional services, ranging from EDI
      format translation, to EDI-to-FAX conversion, to integrated
      business systems.

   $ VAN
      See: value-added network.

   $ verification
      1. System verification: The process of comparing two levels of
      system specification for proper correspondence, such as comparing
      a security policy with a top-level specification, a top-level
      specification with source code, or source code with object code.
      [NCS04]

      2. Identification verification: Presenting information to
      establish the truth of a claimed identity.

   $ verify
      See: validate vs. verify.


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   $ violation
      See: security violation.

   $ virtual private network (VPN)
      (I) A restricted-use, logical (i.e., artificial or simulated)
      computer network that is constructed from the system resources of
      a relatively public, physical (i.e., real) network (such as the
      Internet), often by using encryption (located at hosts or
      gateways), and often by tunneling links of the virtual network
      across the real network.

      (C) For example, if a corporation has LANs at several different
      sites, each connected to the Internet by a firewall, the
      corporation could create a VPN by using encrypted tunnels to
      connect from firewall to firewall across the Internet and not
      allowing any other traffic through the firewalls. A VPN is
      generally less expensive to build and operate than a dedicated
      real network, because the virtual network shares the cost of
      system resources with other users of the real network.

   $ virus
      (I) A hidden, self-replicating section of computer software,
      usually malicious logic, that propagates by infecting--i.e.,
      inserting a copy of itself into and becoming part of--another
      program. A virus cannot run by itself; it requires that its host
      program be run to make it active.

   $ VPN
      See: virtual private network.

   $ vulnerability
      (I) A flaw or weakness in a system's design, implementation, or
      operation and management that could be exploited to violate the
      system's security policy.

      (C) Most systems have vulnerabilities of some sort, but this does
      not mean that the systems are too flawed to use. Not every threat
      results in an attack, and not every attack succeeds. Success
      depends on the degree of vulnerability, the strength of attacks,
      and the effectiveness of any countermeasures in use. If the
      attacks needed to exploit a vulnerability are very difficult to
      carry out, then the vulnerability may be tolerable. If the
      perceived benefit to an attacker is small, then even an easily
      exploited vulnerability may be tolerable. However, if the attacks
      are well understood and easily made, and if the vulnerable system
      is employed by a wide range of users, then it is likely that there
      will be enough benefit for someone to make an attack.

   $ W3
      See: World Wide Web.



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   $ war dialer
      (I) A computer program that automatically dials a series of
      telephone numbers to find lines connected to computer systems, and
      catalogs those numbers so that a cracker can try to break into the
      systems.

   $ Wassenaar Arrangement
      (N) The Wassenaar Arrangement on Export Controls for Conventional
      Arms and Dual-Use Goods and Technologies is a global, multilateral
      agreement approved by 33 countries in July 1996 to contribute to
      regional and international security and stability, by promoting
      information exchange concerning, and greater responsibility in
      transfers, thus preventing destabilizing accumulations. (See:
      International Traffic in Arms Regulations.)

      (C) The Arrangement began operations in September 1996. The
      participating countries are Argentina, Australia, Austria,
      Belgium, Bulgaria, Canada, Czech Republic, Denmark, Finland,
      France, Germany, Greece, Hungary, Ireland, Italy, Japan,
      Luxembourg, Netherlands, New Zealand, Norway, Poland, Portugal,
      Republic of Korea, Romania, Russian Federation, Slovak Republic,
      Spain, Sweden, Switzerland, Turkey, Ukraine, United Kingdom, and
      United States. Participants meet on a regular basis in Vienna,
      where the Arrangement has its headquarters.

      Participating countries seek through their national policies to
      ensure that transfers do not contribute to the development or
      enhancement of military capabilities that undermine the goals of
      the arrangement, and are not diverted to support such
      capabilities. The countries maintain effective export controls for
      items on the agreed lists, which are reviewed periodically to
      account for technological developments and experience gained.
      Through transparency and exchange of views and information,
      suppliers of arms and dual-use items can develop common
      understandings of the risks associated with their transfer and
      assess the scope for coordinating national control policies to
      combat these risks. Members provide semi-annual notification of
      arms transfers, covering seven categories derived from the UN
      Register of Conventional Arms. Members also report transfers or
      denials of transfers of certain controlled dual-use items.
      However, the decision to transfer or deny transfer of any item is
      the sole responsibility of each participating country. All
      measures undertaken with respect to the arrangement will be in
      accordance with national legislation and policies and will be
      implemented on the basis of national discretion.

   $ watermarking
      See: digital watermarking.

   $ web vs. Web
      1. (I) Capitalized: ISPDs SHOULD capitalize "the Web" when using
      the term (usually as a noun) to refer specifically to the World


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      Wide Web. (Similarly, see: internet vs. Internet.)

      2. (C) Not capitalized: ISPD SHOULD NOT capitalize "web" when
      using the term (usually as an adjective) to refer generically to
      technology--such as web browsers, web servers, HTTP, and HTML--
      that is used in the Web or similar networks.

      (C) IETF documents SHOULD spell out "World Wide Web" fully at the
      first instance of usage and SHOULD Use "Web" and "web" especially
      carefully where confusion with the PGP web of trust is possible.

   $ web of trust
      (O) PGP usage: A trust-file PKI technique used in PGP for building
      a file of validated public keys by making personal judgments about
      being able to trust certain people to be holding properly
      certified keys of other people. (Compare with: certification
      hierarchy, mesh PKI.)

   $ web server
      (I) A software process that runs on a host computer connected to
      the Internet to respond to HTTP requests for documents from client
      web browsers.

   $ wiretapping
      (I) An attack that intercepts and accesses data flowing between
      two points in a communication system.

      (C) Although the term originally referred to making a mechanical
      connection to an electrical conductor, it is now used to refer to
      reading information from any sort of medium used for a link, or
      even from a gateway or a subnetwork switch.)

      (C) "Active wiretapping" (see: active attack) attempts to alter
      the data or otherwise affect the flow; "passive wiretapping" (see:
      passive attack) only attempts to observe and gain knowledge of the
      data. (See: end-to-end encryption.)

   $ work factor
      (I) General security usage: The estimated amount of effort or time
      that can be expected to be expended by a potential intruder to
      penetrate a system, or defeat a particular countermeasure, when
      using specified amounts of expertise and resources.

      (I) Cryptography usage: The estimated amount of computing time and
      power needed to break a cryptographic system.

   $ World Wide Web ("the Web", WWW, W3)
      (N) The global, hypermedia-based collection of information and
      services that is available on Internet servers and is accessed by
      browsers using Hypertext Transfer Protocol and other information
      retrieval mechanisms. (See: web vs. Web, [R2084].)



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   $ worm
      (I) A computer program that can run independently, can propagate a
      complete working version of itself onto other hosts on a network,
      and may consume computer resources destructively. (See: Morris
      Worm, virus.)

   $ wrap
      (I) To use cryptography to provide data confidentiality service
      for a data set. (See: encrypt, seal.)

      (D) ISPDs SHOULD NOT use this term with this definition because it
      duplicates the meaning of other, standard terms. Instead, use
      "encrypt" or use a term that is specific with regard to the
      mechanism used.

   $ WWW
      See: World Wide Web.

   $ X.400
      (N) An ITU-T Recommendation [X400] that is one part of a joint
      ITU-T/ISO multi-part standard (X.400-X.421) that defines the
      Message Handling Systems. (The ISO equivalent is IS 10021, parts
      1-7.) (See: Message Handling Systems.)

   $ X.500
   $ X.500 Directory
      (N) An ITU-T Recommendation [X500] that is one part of a joint
      ITU-T/ISO multi-part standard that defines the X.500 Directory, a
      conceptual collection of systems that provide distributed
      directory capabilities for OSI entities, processes, applications,
      and services. (The ISO equivalent is IS 9594-1 and related
      standards, IS 9594-x.) (See: directory vs. Directory, X.509.)

      (C) The X.500 Directory is structured as a tree (the Directory
      Information Tree), and information is stored in directory entries.
      Each entry is a collection of information about one object, and
      each object has a unique DN. An entry is composed of attributes,
      each with a type and one or more values. For example, if a PKI
      uses the Directory to distribute certificates, then an X.509
      public-key certificate of an end user is normally stored as a
      value of an attribute of type "userCertificate" in the Directory
      entry that has the DN that is the subject of the certificate.

   $ X.509
      (N) An ITU-T Recommendation [X509] that is one part of a joint
      ITU-T/ISO multi-part standard (see: X.500). X.509 defines a
      framework to provide and support data origin authentication and
      peer entity authentication, including formats for X.509 public-key
      certificates, X.509 attribute certificates, and X.509 CRLs. (The
      ISO equivalent is IS 9498-4.) (See: X.500.)

      (C) X.509 describes two levels of authentication: simple


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      authentication based on a password, and strong authentication
      based on a public-key certificate. (See: X.509 public-key
      certificate.)

   $ X.509 attribute certificate
      (N) An attribute certificate in the version 1 (v1) format defined
      by X.509. (The v1 designation for an X.509 attribute certificate
      is disjoint from the v1 designation for an X.509 public-key
      certificate, and from the v1 designation for an X.509 CRL.)

      (C) An X.509 attribute certificate has a subject field, but the
      attribute certificate is a separate data structure from that
      subject's public-key certificate. A subject may have multiple
      attribute certificates associated with each of its public-key
      certificates, and an attribute certificate may be issued by a
      different CA than the one that issued the associated public-key
      certificate.

      (C) An X.509 attribute certificate contains a sequence of data
      items and has a digital signature is computed on that sequence. In
      addition to the signature, an attribute certificate contains items
      1 through 9 listed below:

      1. version                Identifies v1.
      2. subject                Is one of the following:
         2a. baseCertificateID   - Issuer and serial number of an
                                   X.509 public-key certificate.
         2b. subjectName         - DN of the subject.
      3. issuer                 DN of the issuer (the CA who signed).
      4. signature              OID of algorithm that signed the cert.
      5. serialNumber           Certificate serial number;
                                an integer assigned by the issuer.
      6. attCertValidityPeriod  Validity period; a pair of UTCTime
                                values: "not before" and "not after".
      7. attributes             Sequence of attributes describing the
                                subject.
      8. issuerUniqueId         Optional, when a DN is not sufficient.
      9. extensions             Optional.

   $ X.509 authority revocation list
      (N) An ARL in one of the formats defined by X.509--version 1 (v1)
      or version 2 (v2). A specialized kind of certificate revocation
      list.

   $ X.509 certificate
      (N) Either an X.509 public-key certificate or an X.509 attribute
      certificate.

      (C) This Glossary uses the term with the precise meaning
      recommended here. However, some who use the term may not be aware
      that X.509 specifies attribute certificates that do not contain a
      public key. Even among those who are aware, this term is commonly


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      used as an abbreviation to mean "X.509 public-key certificate".
      ISPDs MAY use the term as an abbreviation for "X.509 public-key
      certificate", but only after using the full term at the first
      instance.

      (D) ISPDs SHOULD NOT use this term as an abbreviation to mean
      "X.509 attribute certificate".

   $ X.509 certificate revocation list (CRL)
      (N) A CRL in one of the formats defined by X.509--version 1 (v1)
      or version 2 (v2). (The v1 and v2 designations for an X.509 CRL
      are disjoint from the v1 and v2 designations for an X.509 public-
      key certificate, and from the v1 designation for an X.509
      attribute certificate.)

      (C) ISPDs SHOULD NOT refer to an X.509 CRL as a digital
      certificate, but note that an X.509 CRL does meet this Glossary's
      definition of "digital certificate". Like a digital certificate,
      an X.509 CRL makes an assertion and is signed by a CA. But instead
      of binding a key or other attributes to a subject, an X.509 CRL
      asserts that certain previously-issued X.509 certificates have
      been revoked (see: certificate revocation).

      (R) An X.509 CRL contains a sequence of data items and has a
      digital signature computed on that sequence. In addition to the
      signature, both v1 and v2 contain items 2 through 6b listed below.
      Version 2 may optionally contain items 1, 6b, and 7.

      1. version                Optional. If present, identifies v2.
      2. signature              OID of the algorithm that signed CRL.
      3. issuer                 DN of the issuer (the CA who signed).
      4. thisUpdate             A UTCTime value.
      5. nextUpdate             A UTCTime value..br
      6. revokedCertificates    3-tuples of 6a, 6b, and (optional) 6c:
         6a. userCertificate    A certificate's serial number.
         6b. revocationDate     UTCTime value for the revocation date.
         6c. crlEntryExtensions Optional.
      7. crlExtensions          Optional.

   $ X.509 public-key certificate
      (N) A public-key certificate in one of the formats defined by
      X.509--version 1 (v1), version 2 (v2), or version 3 (v3). (The v1
      and v2 designations for an X.509 public-key certificate are
      disjoint from the v1 and v2 designations for an X.509 CRL, and
      from the v1 designation for an X.509 attribute certificate.)

      (C) An X.509 public-key certificate contains a sequence of data
      items and has a digital signature computed on that sequence. In
      addition to the signature, all three versions contain items 1
      through 7 listed below. Only v2 and v3 certificates may also
      contain items 8 and 9, and only v3 may contain item 10.



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      1. version                 Identifies v1, v2, or v3.
      2. serialNumber            Certificate serial number;
                                 an integer assigned by the issuer.
      3. signature               OID of algorithm that was used to
                                 sign the certificate.
      4. issuer                  DN of the issuer (the CA who signed).
      5. validity                Validity period; a pair of UTCTime
                                 values: "not before" and "not after".
      6. subject                 DN of entity who owns the public key.
      7. subjectPublicKeyInfo    Public key value and algorithm OID.
      8. issuerUniqueIdentifier  Defined for v2, v3; optional.
      9. subjectUniqueIdentifier Defined for v2, v2; optional.
      10. extensions             Defined only for v3; optional.

   $ XTACACS
      See: (secondary definition in) Terminal Access Controller (TAC)
      Access Control System.

   $ Yellow Book
      (D) ISPDs SHOULD NOT use this term as a synonym for "Computer
      Security Requirements: Guidance for Applying the Department of
      Defense Trusted Computer System Evaluation Criteria in Specific
      Environments" [CSC3]. Instead, use the full proper name of the
      document or, in subsequent references, a conventional
      abbreviation. (See: (usage note under) Green Book, Rainbow
      Series.)

   $ zeroize
      (I) Use erasure or other means to render stored data--particularly
      a key stored in a cryptographic module or other device--unusable
      and unrecoverable.

      (O) Erase electronically stored data by altering the contents of
      the data storage so as to prevent the recovery of the data.
      [FP140]



















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4. References

   [ABA]   American Bar Association, "Digital Signature Guidelines:
           Legal Infrastructure for Certification Authorities and
           Secure Electronic Commerce", Chicago, IL, 1 Aug 1996.

   [ACM]   Association for Computing Machinery, "Communications of the
           ACM", Jul 1998 issue with: Minerva M. Yeung, "Digital
           Watermarking"; Nasir Memom and Ping Wah Wong, "Protecting
           Digital Media Content"; and Scott Craver, Boon-Lock Yeo, and
           Minerva Yeung, "Technical Trials and Legal Tribulations".

   [A3092] American National Standards Institute, "American National
           Standard Data Encryption Algorithm", ANSI X3.92-1981, 30 Dec
           1980.

   [A9009] ---, "Financial Institution Message Authentication
           (Wholesale)", ANSI X9.9-1986, 15 Aug 1986.

   [A9017] ---, "Financial Institution Key Management (Wholesale)",
           X9.17, 4 Apr 1985. [Defines procedures for the manual and
           automated management of keying material and uses DES to
           provide key management for a variety of operational
           environments.]

   [A9042] ---, "Public key Cryptography for the Financial Service
           Industry: Agreement of Symmetric Keys Using Diffie-Hellman
           and MQV Algorithms", X9.42, 29 Jan 1999.

   [A9052] ---, "Triple Data Encryption Algorithm Modes of Operation",
           X9.52-1998, ANSI approval 9 Nov 1998.

   [A9062] ---, "Public Key Cryptography for the Financial Services
           Industry: The Elliptic Curve Digital Signature Algorithm
           (ECDSA)", X9.62-1998, ANSI approval 7 Jan 1999.

   [B7799] British Standards Institution, "Information Security
           Management, Part 1: Code of Practice for Information
           Security Management", BS 7799-1:1999.
           ---, ---, "Part 2: Specification for Information Security
           Management Systems", BS 7799-2:1999.

   [CCIB]  Common Criteria Implementation Board, "Common Criteria for
           Information Technology Security Evaluation, Part 1:
           Introduction and General Model", ver. 2.0, CCIB-98-026, May
           1998.

   [CIPSO] Trusted Systems Interoperability Working Group, "Common IP
           Security Option", ver. 2.3, 9 Mar 1993.

   [CSC1]  [U.S.]Department of Defense Computer Security Center,
           "Department of Defense Trusted Computer System Evaluation


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           Criteria", CSC-STD-001-83, 15 Aug 1983. (Superseded by
           [DOD1].)

   [CSC2]  ---, "Department of Defense Password Management Guideline",
           CSC-STD-002-85, 12 Apr 1985.

   [CSC3]  ---, "Computer Security Requirements: Guidance for Applying
           the Department of Defense Trusted Computer System Evaluation
           Criteria in Specific Environments", CSC-STD-003-85, 25 Jun
           1985.

   [CSOR]  U.S. Department of Commerce, "General Procedures for
           Registering Computer Security Objects", National Institute
           of Standards Interagency Report 5308, Dec 1993.

   [Denn]  D. E. Denning, "A Lattice Model of Secure Information Flow",
           in "Communications of the ACM", vol. 19, no. 5, May 1976,
           pp. 236-243.

   [DH76]  W. Diffie and M. H. Hellman, "New Directions in Cryptography"
           in "IEEE Transactions on Information Theory", vol. IT-22,
           no. 6, Nov 1976, pp. 644-654.

   [DOD1]  U.S. Department of Defense, "Department of Defense Trusted
           Computer System Evaluation Criteria", DoD 5200.28-STD, 26
           Dec 1985. (Supersedes [CSC1].)

   [DOD2]  ---, Directive 5200.28, "Security Requirements for Automated
           Information Systems (AISs)", 21 Mar 1988.

   [DOD3]  ---, "X.509 Certificate Policy", ver. 2, Mar 1999.

   [DOD98] ---, "NSA Key Recovery Assessment Criteria", 8 Jun 1998.

   [EMV1]  Europay International S.A., MasterCard International
           Incorporated, and Visa International Service Association,
           "EMV '96 Integrated Circuit Card Specification for Payment
           Systems", ver. 3.1.1, 31 May 1998.

   [EMV2]  ---, "EMV '96 Integrated Circuit Card Terminal Specification
           for Payment Systems", ver. 3.1.1, 31 May 1998.

   [EMV3]  ---, EMV '96 Integrated Circuit Card Application
           Specification for Payment Systems", ver. 3.1.1, 31 May 1998.

   [For94] W. Ford, "Computer Communications Security: Principles,
           Standard Protocols and Techniques", ISBN 0-13-799453-2,
           1994.

   [For97] W. Ford and M. Baum, "Secure Electronic Commerce: Building
           the Infrastructure for Digital Signatures and Encryption",
           ISBN 0-13-476342-4, 1994.


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   [FP031] U.S. Department of Commerce, "Guidelines for Automatic Data
           Processing Physical Security and Risk Management", Federal
           Information Processing Standards Publication (FIPS PUB) 31,
           Jun 1974.


   [FP039] ---, "Glossary for Computer Systems Security", Federal
           Information Processing Standards Publication (FIPS PUB) 39,
           15 Feb 1976.

   [FP046] ---, "Data Encryption Standard (DES)", FIPS PUB 46-2, 30 Dec
           1993.

   [FP081] ---, "DES Modes of Operation", FIPS PUB 81, 2 Dec 1980.

   [FP102] ---, "Guideline for Computer Security Certification and
           Accreditation", FIPS PUB 102, 27 Sep 1983.

   [FP113] ---, "Computer Data Authentication", FIPS PUB 113, 30 May
           1985.

   [FP140] ---, "Security Requirements for Cryptographic Modules", FIPS
           PUB 140-1, 11 Jan 1994.

   [FP151] ---, "Portable Operating System Interface (POSIX)--System
           Application Program Interface [C Language]", FIPS PUB 151-2,
           12 May 1993

   [FP180] ---, "Secure Hash Standard", FIPS PUB 180-1, 17 Apr 1995.

   [FP185] ---, "Escrowed Encryption Standard", FIPS PUB 185, 9 Feb
           1994.

   [FP186] ---, "Digital Signature Standard (DSS)", FIPS PUB 186, 19 May
           1994.

   [FP188] ---, "Standard Security Label for Information Transfer", FIPS
           PUB 188, 6 Sep 1994.

   [FPDAM] Collaborative ITU and ISO/IEC meeting on the Directory,
           "Final Proposed Draft Amendment on Certificate Extensions",
           April 1999. (This draft proposes changes to [X.509].)
   [FPKI]  U.S. Department of Commerce, "Public Key Infrastructure (PKI)
           Technical Specifications: Part A--Technical Concept of
           Operations", National Institute of Standards, 4 Sep 1998.

   [I3166] International Standards Organization, "Codes for the
           Representation of Names of countries and Their Subdivisions
           --Part 1: Country Codes", ISO 3166-1:1997.




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           ---, --- "Part 2: Country Subdivision Codes", ISO/DIS 3166-2.

           ---, --- "Part 3: Codes for formerly Used Names of
           Countries", ISO/DIS 3166-3.

   [I7498] ---, "Information Processing Systems--Open Systems
           Interconnection Reference Model--[Part 1:] Basic Reference
           Model", ISO/IEC 7498-1. (Equivalent to ITU-T Recommendation
           X.200.)

           ---, --- "Part 2: Security Architecture", ISO/IEC 7499-2.

           ---, --- "Part 4: Management Framework", ISO/IEC 7498-4.

   [I7812] ---, "Identification cards--Identification of issuers--Part
           1: Numbering system, ISO/IEC 7812-1:1993, and Identification
           cards--Identification of issuers--Part 2: Application and
           registration procedures", ISO/IEC 7812-2:1993.

   [I9945] "Portable Operating System Interface for Computer
           Environments", ISO/IEC 9945-1: 1990.

   [ITSEC] "Information Technology Security Evaluation Criteria (ITSEC):
           Harmonised Criteria of France, Germany, the Netherlands, and
           the United Kingdom", ver. 1.2, U.K. Department of Trade and
           Industry, Jun 1991.

   [Kahn]  David Kahn, "The Codebreakers: The Story of Secret Writing",
           The Macmillan Company, New York, 1967.

   [Kuhn]  Markus G. Kuhn and Ross J. Anderson, "Soft Tempest: Hidden
           Data Transmission Using Electromagnetic Emanations", in
           David Aucsmith, ed., "Information Hiding, Second
           International Workshop, IH'98", Portland, Oregon, USA, 15-17
           Apr 1998, LNCS 1525, Springer-Verlag, ISBN 3-540-65386-4,
           pp. 124-142.

   [MISPC] U.S. Department of Commerce, "Minimum Interoperability
           Specification for PKI Components (MISPC), Version 1",
           National Institute of Standards Special Publication 800-15,
           Sep 1997.

   [NCS01] National Computer Security Center, "A Guide to Understanding
           Audit in Trusted Systems", NCSC-TG-001, 1 Jun 1988. (Part of
           the Rainbow Series.)

   [NCS04] ---, "Glossary of Computer Security Terms", NCSC-TG-004, ver.
           1, 21 Oct 1988. (Part of the Rainbow Series.)

   [NCS05] ---, "Trusted Network Interpretation of the Trusted Computer
           System Evaluation Criteria", NCSC-TG-005, ver. 1, 31 Jul
           1987. (Part of the Rainbow Series.)


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   [NCS25] ---, "A Guide to Understanding Data Remanence in Automated
           Information Systems", NCSC-TG-025, ver. 2, Sep 1991. (Part
           of the Rainbow Series.)

   [PGP]   Simson Garfinkel, "PGP: Pretty Good Privacy", O'Reilly &
           Associates, Inc., Sebastopol, California, 1995.

   [PKCS]  Burton S. Kaliski, Jr., "An Overview of the PKCS Standards",
           RSA Data Security, Inc., 3 Jun 1991.

   [PKC07] RSA Laboratories, "PKCS #7: Cryptographic Message Syntax
           Standard", ver. 1.5, RSA Laboratories Technical Note, 1 Nov
           1993.

   [PKC10] ---, "PKCS #10: Certification Request Syntax Standard", ver.
           1.0, RSA Laboratories Technical Note, 1 Nov 1993

   [PKC11] ---, "PKCS #11: Cryptographic Token Interface Standard", ver.
           1.0, 28 Apr 1995.

   [R0768] J. Postel, "User Datagram Protocol", STD 6, RFC 768, 28 Aug
           1980.

   [R0791] ---, "Internet Protocol", STD 5, RFC 791, 1 Sep 1981.

   [R0792] ---, "Internet Control Message Protocol", STD 5, RFC 792, Sep
           1981. [See: RFC 1885.]

   [R0793] ---, ed., "Transmission Control Protocol", STD 7, RFC 793,
           Sep 1981.

   [R0821] ---, "Simple Mail Transfer Protocol", STD 10, RFC 821, Aug
           1982.

   [R0822] D. H. Crocker, "Standard for the Format of ARPA Internet Text
           Messages", STD 11, RFC 822, 13 Aug 1982.

   [R0854] J. Postel and J. Reynolds, "TELNET Protocol Specification",
           STD 8, RFC 854, May 1983.

   [R0959] ---, "File Transfer Protocol (FTP)", STD 9, RFC 959, Oct
           1985.

   [R1034] P. Mockapetris, "Domain Names--Concepts and Facilities", STD
           13, RFC 1034, Nov 1987.

   [R1157] J. Case, M. Fedor, M. Schoffstall, and J. Davin, "A Simple
           Network Management Protocol (SNMP)", STD 15, RFC 1157, May
           1990.




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   [R1208] O. Jacobsen and D. Lynch, "A Glossary of Networking Terms",
           RFC 1208, Mar 1991.

   [R1319] B. Kaliski, "The MD2 Message-Digest Algorithm", RFC 1319, Apr
           1992.

   [R1320] R. Rivest, "The MD4 Message-Digest Algorithm", RFC 1320, Apr
           1992.

   [R1321] ---, "The MD5 Message-Digest Algorithm", RFC 1321, Apr 1992.

   [R1334] B. Lloyd, W. Simpson, "PPP Authentication Protocols", RFC
           1334, Oct 1992.

   [R1413] M. St. Johns, "Identification Protocol", RFC 1413, Feb 1993.

   [R1421] J. Linn, "Privacy Enhancement for Internet Electronic Mail,
           Part I: Message Encryption and Authentication Procedures",
           RFC 1421, Feb 1993.

   [R1422] S. Kent, "Privacy Enhancement for Internet Electronic Mail,
           Part II: Certificate-Based Key Management", RFC 1422, Feb
           1993.

   [R1455] D. Eastlake, III, "Physical Link Security Type of Service",
           RFC 1455, May 1993.

   [R1457] R. Housley, "Security Label Framework for the Internet", RFC
           1457, May 1993.

   [R1492] C. Finseth, "An Access Control Protocol, Sometimes Called
           TACACS", RFC 1492, Jul 1993.

   [R1507] C. Kaufman, "DASS: Distributed Authentication Security
           Service", RFC 1507, Sep 1993.

   [R1510] J. Kohl and C. Neuman, "The Kerberos Network Authentication
           Service (V5)", RFC 1510, Sep 1993

   [R1591] ---, "Domain Name System Structure and Delegation", Mar 1994.

   [R1630] T. Berners-Lee, "Universal Resource Identifiers in WWW", RFC
           1630, Jun 1994.

   [R1731] J. Myers, "IMAP4 Authentication Mechanisms", RFC 1731, Dec
           1994.

   [R1734] ---, "POP3 AUTHentication Command", RFC 1734, Dec, 1994.

   [R1738] ---, L. Masinter, and M. McCahill, ed's., "Uniform Resource
           Locators (URL)", RFC 1738, Dec 1994.



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   [R1750] D. Eastlake, 3rd, S. Crocker, and J. Schiller, "Randomness
           Recommendations for Security", Dec 1994.

   [R1777] W. Yeong, T. Howes, and S. Kille, "Lightweight Directory
           Access Protocol", Mar 1995

   [R1808] R. Fielding, "Relative Uniform Resource Locators", RFC 1808,
           Jun 1995

   [R1824] H. Danisch, "The Exponential Security System TESS: An
           Identity-Based Cryptographic Protocol for Authenticated Key-
           Exchange (E.I.S.S.-Report 1995/4)", RFC 1824, Aug 1995.

   [R1828] P. Metzger and W. Simpson, "IP Authentication using Keyed
           MD5", RFC 1828, Aug 1995.

   [R1829] P. Karn, P. Metzger, and W. Simpson, "The ESP DES-CBC
           Transform", RFC 1829, Aug 1995.

   [R1848] S. Crocker, N. Freed, J. Galvin, and S. Murphy, "MIME Object
           Security Services", RFC 1848, Oct 1995.

   [R1851] P. Karn, P. Metzger, and W. Simpson, "The ESP Triple DES
           Transform", RFC 1851, Sep 1995.

   [R1866] T. Berners-Lee, "Hypertext Markup Language--2.0", RFC 1866,
           Nov 1995.

   [R1885] A. Conta and S. Deering, "Internet Control Message Protocol
           (ICMPv6) for the Internet Protocol Version 6 (IPv6)
           Specification", RFC 1885, Dec 1995.

   [R1928] M. Leech, M. Ganis, Y. Lee, R. Kuris, D. Koblas, and L.
           Jones, "SOCKS Protocol Version 5", RFC 1928, Mar 1996.

   [R1938] N. Haller and C. Metzion, "A One-Time Password System", RFC
           1938, May 1996.

   [R1939] J. Myers and M. Rose, "Post Office Protocol - Version 3", RFC
           1939, May 1996.

   [R1958] B. Carpenter, ed., "Architectural Principles of the
           Internet", RFC 1958, Jun 1996.

   [R1983] G. Malkin, ed., "Internet Users' Glossary", RFC 1983, FYI 18,
           Aug 1996.

   [R1994] W. Simpson, "PPP Challenge Handshake Authentication Protocol
           (CHAP)", RFC 1994, Aug 1996.





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   [R2023] J. Postel and J. Reynolds, "Instructions to RFC Authors", RFC
           2023, Oct 1997.

   [R2026] S. Bradner, "The Internet Standards Process--Revision 3",
           BCP009, RFC 2026, Mar 1994.

   [R2045] N. Freed and N. Borenstein, "Multipurpose Internet Mail
           Extensions (MIME) Part One: Format of Internet Message
           Bodies", RFC 2045, Nov 1996.

   [R2060] M. Crispin, "Internet Message Access Protocol--Version 4
           Revision 1", RFC 2060, Dec 1996.

   [R2065] D. Eastlake, 3rd, "Domain Name System Security Extensions",
           RFC 2065, Jan 1997.

   [R2068] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-Lee,
           "Hypertext Transfer Protocol--HTTP/1.1", RFC 2068, Jan 1997.

   [R2078] J. Linn, "Generic Security Service Application Program
           Interface, Version 2", RFC 2078, Jan 1997.

   [R2084] G. Bossert, S. Cooper, and W. Drummond, "Considerations for
           Web Transaction Security", RFC 2084, Jan 1997.

   [R2104] H. Krawczyk, M. Bellare, and R. Canetti, "HMAC: Keyed-Hashing
           for Message Authentication", RFC 2104, Feb 1997.

   [R2137] D. Eastlake, 3rd, "Secure Domain Name System Dynamic Update",
           RFC 2137, Apr 1997.

   [R2179] A. Gwinn, "Network Security For Trade Shows", RFC 2179, Jul
           1997.

   [R2195] J. Klensin, R. Catoe, and P. Krumviede, "IMAP/POP AUTHorize
           Extension for Simple Challenge/Response", RFC 2195, Sep
           1997.

   [R2196] B. Fraser, "Site Security Handbook", RFC 2196, Sep 1997.

   [R2202] P. Cheng and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
           SHA-1", RFC 2202, Sep. 1997.

   [R2222] J. Myers, "Simple Authentication and Security Layer (SASL)",
           RFC 2222, Oct 1997.

   [R2284] L. Blunk and J. Vollbrecht, "PPP Extensible Authentication
           Protocol (EAP)", RFC 2284, Mar 1998.

   [R2315] B. Kaliski, "PKCS #7: Cryptographic Message Syntax, Version
           1.5", RFC 2315, Mar 1998.



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   [R2323] A. Ramos, "IETF Identification and Security Guidelines", RFC
           2323, 1 Apr 1998. [Intended for humorous entertainment
           ("please laugh loud and hard"); does not contain serious
           security information.]

   [R2350] N. Brownlee and E. Guttman, "Expectations for Computer
           Security Incident Response", RFC 2350, Jun 1998.

   [R2373] R. Hinden and S. Deering, "IP Version 6 Addressing
           Architecture", RFC 2373.

   [R2401] S. Kent and R. Atkinson, "Security Architecture for the
           Internet Protocol", RFC 2401, Nov 1998.

   [R2402] S. Kent and R. Atkinson, "IP Authentication Header", RFC
           2402, Nov 1998.

   [R2403] C. Madson and R. Glenn, "The Use of HMAC-MD5-96 within ESP
           and AH", RFC 2403, Nov 1998.

   [R2404] C. Madson and R. Glenn, "The Use of HMAC-SHA-1-96 within ESP
           and AH", RFC 2404, Nov 1998.

   [R2405] C. Madson and N. Doraswamy, "The ESP DES-CBC Cipher Algorithm
           With Explicit IV", RFC 2405, Nov 1998.

   [R2406] S. Kent and R. Atkinson, "IP Encapsulating Security Payload
           (ESP)", RFC 2406, Nov 1998.

   [R2407] D. Piper, "The Internet IP Security Domain of Interpretation
           for ISAKMP", RFC 2407, Nov 1998.

   [R2408] D. Maughan, M. Schertler, M. Schneider, and J. Turner,
           "Internet Security Association and Key Management Protocol
           (ISAKMP)", RFC 2408, Nov 1998.

   [R2409] D. Harkins and D. Carrel, "The Internet Key Exchange (IKE)",
           RFC 2409, Nov 1998.

   [R2410] R. Glenn and S. Kent, "The NULL Encryption Algorithm and Its
           Use With IPsec", RFC 2410, Nov 1998.

   [R2412] H. Orman, "The OAKLEY Key Determination Protocol", RFC 2412,
           Nov 1998.

   [R2451] R. Pereira and R. Adams, "The ESP CBC-Mode Cipher
           Algorithms", RFC 2451, Nov 1998.

   [R2460] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6)
           Specification", RFC 2460, Dec 1998.




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   [R2504] E. Guttman, L. Leong, and G. Malkin, "Users' Security
           Handbook", RFC 2504, Feb 1999.

   [R2510] C. Adams and S. Farrell, "Internet X.509 Public Key
           Infrastructure Certificate Management Protocols", RFC 2510,
           Mar 1999.

   [R2527] S. Chokhani and W. Ford, "Internet X.509 Public Key
           Infrastructure, Certificate Policy and Certification
           Practices Framework", RFC 2527, Mar 1999.

   [R2570] J. Case, R. Mundy, D. Partain, B. Stewart, "Introduction to
           Version 3 of the Internet-Standard Network Management
           Framework", RFC 2570, Apr 1999.

   [R2574] U. Blumenthal and B. Wijnen, "User-based Security Model (USM)
           for Version 3 of the Simple Network Management Protocol
           (SNMPv3)", RFC 2574, Apr 1999.

   [R2612] C. Adams and J. Gilchrist, "The CAST-256 Encryption
           Algorithm", RFC 2612, Jun 1999.

   [R2628] V. Smyslov, "Simple Cryptographic Program Interface", RFC
           2628, Jun 1999.

   [R2630] R. Housley, "Cryptographic Message Syntax", RFC 2630, Jun
           1999.

   [R2631] E. Rescorla, "Diffie-Hellman Key Agreement Method", RFC 2631,
           Jun 1999

   [R2633] B. Ramsdell, ed., "S/MIME Version 3 Message Specification",
           RFC 2633, Jun 1999

   [R2634] P. Hoffman, ed., "Enhanced Security Services for S/MIME", RFC
           2634, Jun 1999

   [R2635] S. Hambridge and A. Lunde, "Don't Spew: A Set of Guidelines
           for Mass Unsolicited Mailings and Postings", RFC 2635, Jun
           1999.

   [Raym]  E. S. Raymond, ed., "The On-Line Hacker Jargon File", ver.
           4.0.0, 24 JUL 1996. (See: http://www.tuxedo.org/jargon/ for
           the latest version. Also, ver. 3.0.0 is available as "The
           New Hacker's Dictionary", 2nd edition, MIT Press, Sep 1993,
           ISBN 0-262-18154-1.)

   [Schn]  B. Schneier, "Applied Cryptography", John Wiley & Sons, Inc.,
           New York, 1994.





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   [SDNS3] National Security Agency, "Secure Data Network Systems,
           Security Protocol 3 (SP3)", document SDN.301, Revision 1.5,
           15 May 1989.

   [SDNS4] ---, ---, "Security Protocol 4 (SP4)", document SDN.401,
           Revision 1.2, 12 Jul 1988.

   [SDNS7] ---, ---, "Secure data Network System, Message Security
           Protocol (MSP)", document SDN.701, Revision 4.0, 7 Jun 1996,
           with Corrections to Message Security Protocol, SDN.701, Rev
           4.0", 96-06-07, 30 Aug, 1996.

   [SET1]  MasterCard and Visa, "SET Secure Electronic Transaction
           Specification, Book 1: Business Description", ver. 1.0, 31
           May 1997.

   [SET2]  ---, "SET Secure Electronic Transaction Specification, Book
           2: Programmer's Guide", ver. 1.0, 31 May 1997.

   [Stei]  J. Steiner, C. Neuman, and J. Schiller, "Kerberos: An
           Authentication Service for Open Network Systems" in "Usenix
           Conference Proceedings", Feb 1988.

   [X400]  International Telecommunications Union--Telecommunication
           Standardization Sector (formerly "CCITT"), Recommendation
           X.400, "Message Handling Services: Message Handling System
           and Service Overview".

   [X500]  ---, Recommendation X.500, "Information Technology--Open
           Systems Interconnection--The Directory: Overview of
           Concepts, Models, and Services". (Equivalent to ISO 9594-1.)

   [X501]  ---, Recommendation X.501, "Information Technology--Open
           Systems Interconnection--The Directory: Models".

   [X509]  ---, Recommendation X.509, "Information Technology--Open
           Systems Interconnection--The Directory: Authentication
           Framework". (AKA ISO 9594-8.)

   [X519]  ---, Recommendation X.519, "Information Technology--Open
           Systems Interconnection--The Directory: Protocol
           Specifications".

   [X520]  ---, Recommendation X.520, "Information Technology--Open
           Systems Interconnection--The Directory: Selected Attribute
           Types".

   [X680]  ---, Recommendation X.680, "Information Technology--Abstract
           Syntax Notation One (ASN.1)--Specification of Basic
           Notation", 15 Nov 1994. (Equivalent to ISO/IEC 8824-1.)

   [X690]  ---, Recommendation X.690, "Information Technology--ASN.1


Shirey             (C) GTE / BBN Technologies (1999)          [Page 189]

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           Encoding Rules--Specification of Basic Encoding Rules (BER),
           Canonical Encoding Rules (CER) and Distinguished Encoding
           Rules (DER)", 15 Nov 1994. (Equivalent to ISO/IEC 8825-1.)



















































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5. Security Considerations

   The focus of this document is security terminology, but this document
   does not discuss security issues in the sense of describing or
   analyzing threats to, vulnerabilities of, or countermeasures to
   protect, any specific Internet Standard protocol.

6. Acknowledgments

   Pat Cain, Mike Kong, and Charles Lynn provided meticulous comments on
   an initial version of this document.

7. Author's Address

   Please address all comments to:

   Robert W. Shirey
   GTE / BBN Technologies
   Suite 1200, Mail Stop 30/12B2
   1300 Seventeenth Street North,
   Arlington, VA  22209-3801 USA

   Phone: +1 (703) 284-4641
   Fax:   +1 (703) 284-2766
   Email: rshirey@bbn.com

8. Expiration Date

   This Internet Draft expires on 17 April 2000.

























Shirey             (C) GTE / BBN Technologies (1999)          [Page 191]


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