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PKIX Working Group                                   R. Housley (SPYRUS)
Internet Draft                                          W. Ford (Nortel)
                                                           D. Solo (BBN)
expires in six months                                          June 1996


                   Internet Public Key Infrastructure

               Part I:  X.509 Certificate and CRL Profile

                  <draft-ietf-pkix-ipki-part1-02.txt>


Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   To learn the current status of any Internet-Draft, please check the
   "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).


Abstract

   This is the second draft of the Internet Public Key Infrastructure
   X.509 Certificate and CRL Profile.  Since the first version was
   distributed, ISO has completed work on X.509 Version 3 Certificates
   and X.509 Version 2 Certificate Revocation Lists (CRLs).  Many of the
   Internet community requirements that were in the previous version of
   this document have been included in the final ISO document.  As a
   result, this document has gotten simpler.  Please send comments on
   this document to the ietf-pkix@tandem.com mail list.


1  Executive Summary

   << Write this last. >>




Housley, Ford, & Solo                                           [Page 1]


INTERNET DRAFT                                                 June 1996


2  Requirements and Assumptions

   Goal is to develop a profile and associated management structure to
   facilitate the adoption/use of X.509 certificates within Internet
   applications for those communities wishing to make use of X.509
   technology. Such applications may include WWW, electronic mail, user
   authentication, electronic payment systems, IPSEC, as well as others.
   In order to relieve some of the obstacles to using X.509
   certificates, this document defines a profile to promote the
   development of certificate management systems; development of
   application tools; and interoperability determined by policy, as
   opposed to syntax.

   Some communities will need to supplement, or possibly replace, this
   profile in order to meet the requirements of specialized application
   domains or environments with additional authorization, assurance, or
   operational requirements.  However, for basic applications, common
   representations of frequently used attributes are defined so that
   application developers can obtain necessary information without
   regard to the issuer of a particular certificate or certificate
   revocation list (CRL).

   As supplemental authorization and attribute management tools emerge,
   such as attribute certificates, it may be appropriate to limit the
   authenticated attributes that are included in a certificate.  These
   other management tools may be more appropriate method of conveying
   many authenticated attributes.

2.1  Communication and Topology

   The users of certificates will operate in a wide range of
   environments with respect to their communication topology, especially
   users of secure electronic mail.  This profile supports users without
   high bandwidth, real-time IP connectivity, or high connection
   availablity.  In addition, the profile allows for the presence of
   firewall or other filtered communication.

2.2  Acceptability Criteria

   The goal of the Internet Public Key Infrstructure (PKI) is to meet
   the needs of deterministic, automated identification, authentication,
   access control, and authorization functions.  Support for these
   services determines the attributes contained in the certificate as
   well as the ancillary control information in the certificate such as
   policy data and certification path constraints.






Housley, Ford, & Solo                                           [Page 2]


INTERNET DRAFT                                                 June 1996


2.3  User Expectations

   Users of the Internet PKI are people and processes who use client
   software and are the subjects named in certificates.  These uses
   include readers and writers of electronic mail, the clients for WWW
   browsers, and the key manager for IPSEC within a router.  This
   profile recognizes the limitations of the platforms these users
   employ and the sophistication/attentiveness of the users themselves.
   This manifests itself in minimal user configuration responsibility
   (e.g., root keys, rules), explicit platform usage constraints within
   the certificate, certification path constraints which shield the user
   from many malicious actions, and applications which sensibly automate
   validation functions.

2.4  Administrator Expectations

   As with users, the Internet PKI profile is structured to support the
   individuals who generally operate Certification Authorities (CAs).
   Providing administrators with unbounded choices increases the chances
   that a subtle CA administrator mistake will result in broad
   compromise.  Also, unbounded choices greatly complicates the software
   that must process and validate the  certificates created by the CA.





























Housley, Ford, & Solo                                           [Page 3]


INTERNET DRAFT                                                 June 1996


3  Overview of Approach

   Following is a simplified view of the architectural model assumed by
   the PKIX specifications.

      +---+
      | C |                       +------------+
      | e | <-------------------->| End entity |
      | r |       Operational     +------------+
      | t |       transactions         ^
      |   |      and management        |  Management
      | / |       transactions         |  transactions
      |   |                            |
      | C |    PKI users               v
      | R |             -------+-------+--------+------
      | L |   PKI management   ^                ^
      |   |      entities      |                |
      |   |                    v                |
      | R |                 +------+            |
      | e | <-------------- | RA   | <-----+    |
      | p |   certificate   |      |       |    |
      | o |       publish   +------+       |    |
      | s |                                |    |
      | i |                                v    v
      | t |                            +------------+
      | o | <--------------------------|     CA     |
      | r |   certificate publish      +------------+
      | y |           CRL publish             ^
      |   |                                   |
      +---+                                   |    Management
                                              |    transactions
                                              v
                                          +------+
                                          |  CA  |
                                          +------+

                          Figure 1 - PKI Entities

   The components in this model are:

   end entity:  user of PKI certificates and/or end user system that
                the PKI certifies;
   CA:          certification authority;
   RA:          registration authority, i.e., an optional system to
                which a CA delegates certain manaagement functions;
   repository:  a system or collection of distributed systems that
                store certificates and CRLs and serves as a means of
                distributing these certificates and CRLs to end



Housley, Ford, & Solo                                           [Page 4]


INTERNET DRAFT                                                 June 1996


                entities.

3.1  X.509 Version 3 Certificate

   Application of public key technology requires the user of a public
   key to be confident that the public key belongs to the correct remote
   subject (person or system) with which an encryption or digital
   signature mechanism will be used.  This confidence is obtained
   through the use of public key certificates, which are data structures
   that bind public key values to subject identities.  The binding is
   achieved by having a trusted certification authority (CA) digitally
   sign each certificate.  A certificate has a limited valid lifetime
   which is indicated in its signed contents.  Because a certificate's
   signature and timeliness can be independently checked by a
   certificate-using client, certificates can be distributed via
   untrusted communications and server systems, and can be cached in
   unsecured storage in certificate-using systems.

   The standard known as ITU-T X.509 (formerly CCITT X.509) or ISO/IEC
   9594-8, which was first published in 1988 as part of the X.500
   Directory recommendations, defines a standard certificate format. The
   certificate format in the 1988 standard is called the version 1 (v1)
   format.  When X.500 was revised in 1993, two more fields were added,
   resulting in the version 2 (v2) format.  These two fields are used to
   support directory access control.

   The Internet Privacy Enhanced Mail (PEM) proposals, published in
   1993, include specifications for a public key infrastructure based on
   X.509 v1 certificates [RFC 1422].  The experience gained in attempts
   to deploy RFC 1422 made it clear that the v1 and v2 certificate
   formats are deficient in several respects.  Most importantly, more
   fields were needed to carry information which PEM design and
   implementation experience has proven necessary.  In response to these
   new requirements, ISO/IEC and ANSI X9 developed the X.509 version 3
   (v3) certificate format.  The v3 format extends the v2 format by
   adding provision for additional extension fields.  Particular
   extension field types may be specified in standards or may be defined
   and registered by any organization or community.  In June 1996,
   standardization of the basic v3 format was completed [X.509-AM].

   ISO/IEC and ANSI X9 have also developed a set of standard extensions
   for use in the v3 extensions field [X.509-AM][X9.55].  These
   extensions can convey such data as additional subject identification
   information, key attribute information, policy information, and
   certification path constraints.

   However, the ISO/IEC and ANSI standard extensions are very broad in
   their applicability.  In order to develop interoperable



Housley, Ford, & Solo                                           [Page 5]


INTERNET DRAFT                                                 June 1996


   implementations of X.509 v3 systems for Internet use, it is necessary
   to specify a profile for use of the X.509 v3 extensions tailored for
   the Internet.  It is one goal of this document to specify a profile
   for Internet WWW, electronic mail, and IPSEC applications.
   Environments with additional requirements may build on this profile
   or may replace it.

3.2  Certification Paths and Trust

   A user of a security service requiring knowledge of a public key
   generally needs to obtain and validate a certificate containing the
   required public key.  If the public-key user does not already hold an
   assured copy of the public key of the CA that signed the certificate,
   then it might need an additional certificate to obtain that public
   key.  In general, a chain of multiple certificates may be needed,
   comprising a certificate of the public key owner (the end entity)
   signed by one CA, and zero or more additional certificates of CAs
   signed by other CAs.  Such chains, called certification paths, are
   required because a public key user is only initialized with a limited
   number (often one) of assured CA public keys.

   There are different ways in which CAs might be configured in order
   for public key users to be able to find certification paths.  For
   PEM, RFC 1422 defined a rigid hierarchical structure of CAs.  There
   are three types of PEM certification authority:

   (a)  Internet Policy Registration Authority (IPRA):  This authority,
   operated under the auspices of the Internet Society, acts as the root
   of the PEM certification hierarchy at level 1.  It issues
   certificates only for the next level of authorities, PCAs.  All
   certification paths start with the IPRA.

   (b)  Policy Certification Authorities (PCAs):  PCAs are at level 2 of
   the hierarchy, each PCA being certified by the IPRA.  A PCA must
   establish and publish a statement of its policy with respect to
   certifying users or subordinate certification authorities.  Distinct
   PCAs aim to satisfy different user needs. For example, one PCA (an
   organizational PCA) might support the general electronic mail needs
   of commercial organizations, and another PCA (a high-assurance PCA)
   might have a more stringent policy designed for satisfying legally
   binding signature requirements.

   (c)  Certification Authorities (CAs):  CAs are at level 3 of the
   hierarchy and can also be at lower levels. Those at level 3 are
   certified by PCAs.  CAs represent, for example, particular
   organizations, particular organizational units (e.g., departments,
   groups, sections), or particular geographical areas.




Housley, Ford, & Solo                                           [Page 6]


INTERNET DRAFT                                                 June 1996


   RFC 1422 furthermore has a name subordination rule which requires
   that a CA can only issue certificates for entities whose names are
   subordinate (in the X.500 naming tree) to the name of the CA itself.
   The trust associated with a PEM certification  path is implied by the
   PCA name.  The name subordination rule ensures that CAs below the PCA
   are sensibly constrained as to the set of subordinate entities they
   can certify (e.g., a CA for an organization can only certify entities
   in that organization's name tree). Certificate user systems are able
   to mechanically check that the name subordination rule has been
   followed.

   The RFC 1422 CA hierarchical model has been found to have several
   deficiencies, including:

   (a)  The pure top-down hierarchy, with all ertification paths
   starting from the root, is too restrictive for many purposes.  For
   some applications, verification of certification paths should start
   with a public key of a CA in a user's own domain, rather than
   mandating that verification commence at the top of a hierarchy. In
   many environments, the local domain is often the most trusted.  Also,
   initialization and key-pair-update operations can be more effectively
   conducted between an end entity and a local management system.

   (b)  The name subordination rule introduces undesirable constraints
   upon the X.500 naming system an organization may use.

   (c)  Use of the PCA concept requires knowledge of individual PCAs to
   be built into certificate chain verification logic.  In the
   particular case of Internet mail, this is not a major problem -- the
   PCA name can always be displayed to the human user who can make a
   decision as to what trust to imply from a particular chain.  However,
   in many commercial applications, such as electronic commerce or EDI,
   operator intervention to make policy decisions is impractical.  The
   process needs to be automated to a much higher degree.  In fact, the
   full process of certificate chain processing needs to be
   implementable in trusted software.

   Because of the above shortcomings, it is proposed that more flexible
   CA structures than the RFC 1422 hierarchy be supported by the PKIX
   specifications.  In fact, the main reason for the structural
   restrictions imposed by RFC 1422 was the restricted certificate
   format provided with X.509 v1.  With X.509 v3, most of the
   requirements addressed by RFC 1422 can be addressed using certificate
   extensions, without a need to restrict the CA structures used.  In
   particular, the certificate extensions relating to certificate
   policies obviate the need for PCAs and the constraint extensions
   obviate the need for the name subordination rule.




Housley, Ford, & Solo                                           [Page 7]


INTERNET DRAFT                                                 June 1996


3.3  Revocation

   When a certificate is issued, it is expected to be in use for its
   entire validity period.  However, various circumstances may cause a
   certificate to become invalid prior to the expiration of the validity
   period. Such circumstances might include change of name, change of
   association between subject and CA (e.g., an employee terminates
   employment with an organization), and compromise or suspected
   compromise of the corresponding private key.  Under such
   circumstances, the CA needs to revoke the certificate.

   X.509 defines one method of certificate revocation.  This method
   involves each CA periodically issuing a signed data structure called
   a certificate revocation list (CRL).  A CRL is a time stamped list
   identifying revoked certificates which is signed by a CA and made
   freely available in a public repository.  Each revoked certificate is
   identified in a CRL by its certificate serial number.  When a
   certificate-using system uses a certificate (e.g., for verifying a
   remote user's digital signature), that system not only checks the
   certificate signature and validity but also acquires a suitably-
   recent CRL and checks that the certificate serial number is not on
   that CRL.  The meaning of "suitably-recent" may vary with local
   policy, but it usually means the most recently-issued CRL.  A CA
   issues a new CRL on a regular periodic basis (e.g., hourly, daily, or
   weekly).  Entries are added to CRLs as revocations occur, and an
   entry may be removed when the certificate expiration date is reached.

   An advantage of this revocation method is that CRLs may be
   distributed by exactly the same means as certificates themselves,
   namely, via untrusted communications and server systems.

   One limitation of the CRL revocation method, using untrusted
   communications and servers, is that the time granularity of
   revocation is limited to the CRL issue period.  For example, if a
   revocation is reported now, that revocation will not be reliably
   notified to certificate-using systems until the next periodic CRL is
   issued -- this may be up to one hour, one day, or one week depending
   on the frequency that the CA issues CRLs.

   Another potential problem with CRLs is the risk of a CRL growing to
   an entirely unacceptable size.  In the 1988 and 1993 versions of
   X.509, the CRL for the end-user certificates needed to cover the
   entire population of end-users for one CA.  It is desirable to allow
   such populations to be in the range of thousands, tens of thousands,
   or possibly even hundreds of thousands of users.  The end-user CRL is
   therefore at risk of growing to such sizes, which present major
   communication and storage overhead problems.  With the version 2 CRL
   format, introduced along with the v3 certificate format, it becomes



Housley, Ford, & Solo                                           [Page 8]


INTERNET DRAFT                                                 June 1996


   possible to arbitrarily divide the population of certificates for one
   CA into a number of partitions, each partition being associated with
   one CRL distribution point (e.g., directory entry or URL) from which
   CRLs are distributed.  Therefore, the maximum CRL size can be
   controlled by a CA.  Separate CRL distribution points can also exist
   for different revocation reasons.  For example, routine revocations
   (e.g., name change) may be placed on a different CRL to revocations
   resulting from suspected key compromises, and policy may specify that
   the latter CRL be updated and issued more frequently than the former.

   As with the X.509 v3 certificate format, in order to facilitate
   interoperable implementations from multiple vendors, the X.509 v2 CRL
   format needs to be profiled for Internet use.  It is one goal of this
   document to specify such profiles.

   Furthermore, it is recognized that on-line methods of revocation
   notification may be applicable in some environments as an alternative
   to the X.509 CRL.  On-line revocation checking eliminates the latency
   between a revocation report and CRL the next issue.  Once the
   revocation is reported, any query to the on- line service will
   correctly reflect the certificate validation impacts of the
   revocation.  Therefore, this document will also consider standard
   approaches to on-line revocation notification.

3.4  Operational Protocols

   Operational protocols are required to deliver certificates and CRLs
   to certificate using client systems. Provision is needed for a
   variety of different means of certificate and CRL delivery, including
   request/delivery procedures based on E-mail, http, X.500, and
   WHOIS++.  These specifications include definitions of, and/or
   references to, message formats and procedures for supporting all of
   the above operational environments, including definitions of or
   references to appropriate MIME content types.

3.5  Management Protocols

   Management protocols are required to support on-line interactions
   between Public Key Infrastructure (PKI) components.  For example,
   management protocol might be used between a CA and a client system
   with which a key pair is associated, or between two CAs which cross-
   certify each other.  The set of functions which potentially need to
   be supported by management protocols include:

   (a)  registration:  This is the process whereby a user first makes
   itself known to a CA, prior to that CA issuing  a certificate or
   certificates for that user.




Housley, Ford, & Solo                                           [Page 9]


INTERNET DRAFT                                                 June 1996


   (b)  initialization:  Before a client system can operate securely it
   is necessary to install in it necessary key materials which have the
   appropriate relationship with keys stored elsewhere in the
   infrastructure.  For example, the client needs to be securely
   initialized with the public key of a CA, to be used in validating
   certificate paths.  Furthermore, a client typically needs to be
   initialized with its own key pair(s).

   (c)  certification:  This  is the process in which a CA issues a
   certificate for a user's public key, and returns that certificate to
   the user's client system and/or posts that certificate in a public
   repository.

   (d)  key pair recovery:  As an option, user client key materials
   (e.g., a user's private key used for encryption purposes) may be
   backed up by a CA or a key backup system associated with a CA.  If a
   user needs to recover these backed up key materials (e.g., as a
   result of a forgotten password or a lost key chain file), an on-line
   protocol exchange may be needed to support such recovery.

   (e)  key pair update:  All key pairs need to be updated regularly,
   i.e., replaced with a new key pair, and new certificates issued.

   (f)  revocation request:  An authorized person advises a CA of an
   abnormal situation requiring certificate revocation.

   (g)  cross-certification:  Two CAs exchange the information necessary
   to establish cross-certificates between those CAs.

   Note that on-line protocols are not the only way of implementing the
   above functions.  For all functions there are off-line methods of
   achieving the same result, and this specification does not mandate
   use of on- line protocols.  For example, when hardware tokens are
   used, many of the functions may be achieved through as part of the
   physical token delivery.  Furthermore, some of the above functions
   may be combined into one protocol exchange.  In particular, two or
   more of the registration, initialization, and certification functions
   can be combined into one protocol exchange.

   Part 3 of the PKIX series of specifications defines a set of standard
   message formats supporting the above functions.  The protocols for
   conveying these messages in different environments (on-line, e-mail,
   and WWW) are also specified.

4  Certificate and Certificate Extensions Profile

   The goal of this document is to create a profile for X.509 v3
   certificates that will foster interoperability and a reusable public



Housley, Ford, & Solo                                          [Page 10]


INTERNET DRAFT                                                 June 1996


   key infrastructure.  Since the publication of earlier versions of
   this draft, substantial changes have been made to the Amendment
   [X.509-AM] to X.509 defining version 3 and certificate extensions.
   Those changes have brought the base document into close alignment
   with the recommendations of earlier versions of this draft.  As a
   result, this document provides a concise profile rather than
   attempting to recreate the Amendment as a standalone document.

   Certificates may be used in a wide range of applications and
   environments covering a broad spectrum of interoperability goals and
   a broader spectrum of operational and assurance requirements.  The
   goal of this document is to establish a common baseline for generic
   applications requiring broad interoperability and limited special
   purpose requirements.  In particular, the emphasis will be on
   supporting the use of X.509 v3 certificates for informal internet
   electronic mail, IPSEC, and WWW applications.  Other efforts are
   looking at certificate profiles for payment systems.

4.1  Basic Certificate Fields

   The X.509 v3 certificate basic syntax is as follows.  For signature
   calculation, the certificate is encoded using the ASN.1 distinguished
   encoding rules (DER) [X.208].  ASN.1 DER encoding is a tag, length,
   value encoding system for each element.

   Certificate  ::=  SEQUENCE  {
        tbsCertificate       TBSCertificate,
        signatureAlgorithm   AlgorithmIdentifier,
        signature            BIT STRING  }

   TBSCertificate  ::=  SEQUENCE  {
        version         [0]  Version DEFAULT v1,
        serialNumber         CertificateSerialNumber,
        signature            AlgorithmIdentifier,
        issuer               Name,
        validity             Validity,
        subject              Name,
        subjectPublicKeyInfo SubjectPublicKeyInfo,
        issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                             -- If present, version must be v2 or v3
        subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                             -- If present, version must be v2 or v3
        extensions      [3]  Extensions OPTIONAL
                             -- If present, version must be v3
        }

   Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }




Housley, Ford, & Solo                                          [Page 11]


INTERNET DRAFT                                                 June 1996


   CertificateSerialNumber  ::=  INTEGER

   Validity  ::=  SEQUENCE  {
        notBefore            UTCTime,
        notAfter             UTCTime  }

   UniqueIdentifier  ::=  BIT STRING

   SubjectPublicKeyInfo  ::=  SEQUENCE  {
        algorithm            AlgorithmIdentifier,
        subjectPublicKey     BIT STRING  }

   Extensions  ::=  SEQUENCE OF Extension

   Extension  ::=  SEQUENCE  {
        extnID      OBJECT IDENTIFIER,
        critical    BOOLEAN DEFAULT FALSE,
        extnValue   OCTET STRING  }

   The following items describe a proposed use of the X.509 v3
   certificate for the Internet.

4.1.1  Version

   This field describes the version of the encoded certificate.  When
   extensions are used, as expected in this profile, use X.509 version 3
   (value is 2).  If no extensions are present, but a UniqueIdentifier
   is present, use version 2 (value is 1).  If only basic fields are
   present, use version 1 (the value is omitted from the certificate as
   the default value).

   Implementations should be prepared to accept any version certificate.
   In particular, at a minimum, implementations should recognize version
   3 certificates; determine whether any critical extensions are
   present; and accept certificates without critical extensions even if
   they don't recognize any extensions.  A certificate with an
   unrecognized critical extension must always be rejected.

   Generation of version 2 certificates is not expected by
   implementations based on this profile.

4.1.2  Serial number

   The serial number is an integer assigned by the certification
   authority to each certificate.  It must be unique for each
   certificate issued by a given CA (i.e., the issuer name and serial
   number identify a unique certificate).




Housley, Ford, & Solo                                          [Page 12]


INTERNET DRAFT                                                 June 1996


4.1.3  Signature

   This field contains the algorithm identifier for the algorithm used
   by the CA to sign the certificate.  Section 7.2 lists the supported
   signature algorithms.

4.1.4  Issuer Name

   The issuer name identifies the entity who has signed (and issued the
   certificate).  The issuer identity may be carried in the issuer name
   field and/or the issuerAltName extension.  If identity information is
   present only in the issuerAltName extension, then the issuer name may
   be an empty sequence and the issuerAltName extension must be
   critical.

   << Should we say anything about name constraints here? >>

4.1.5  Validity

   This field indicates the dates on which the certificate becomes valid
   (notBefore) and on which the certificate ceases to be valid
   (notAfter).  It is strongly recommended that UTCTime values be
   expressed Greenwich Mean Time (Zulu) and not use seconds (i.e., times
   are YYMMDDHHMMZ).  If seconds are used, a value of 00 seconds should
   never be encoded.

4.1.6  Subject Name

   The subject name identifies the entity associated with the public key
   stored in the subject public key field. The subject identity may be
   carried in the subject field and/or the subjectAltName extension.  If
   identity information is present only in the subjectAltName extension
   (e.g., a key bound only to an email address or URI), then the subject
   name may be an empty sequence and the subjectAltName extension must
   be critical.

   << Should we say anything about name constraints here? >>

4.1.7  Subject Public Key Info

   This field is used to carry the public key and identify the algorithm
   with which the key is used.

4.1.8  Unique Identifiers

   The subject and issuer unique identifier are present in the
   certificate to handle the possibility of reuse of subject and/or
   issuer names over time.  This profile recommends that names not be



Housley, Ford, & Solo                                          [Page 13]


INTERNET DRAFT                                                 June 1996


   reused and that Internet certificates not make use of unique
   identifiers.  CA's conforming to this profile should not generate
   certificates with unique identifiers.  Applications conforming to
   this profile should be capable of parsing unique identifiers and
   making comparisons.

4.2  Certificate Extensions

   The extensions defined for X.509 v3 certificates provide methods for
   associating additional attributes with users or public keys, for
   managing the certification hierarchy, and for managing CRL
   distribution.  The X.509 v3 certificate format also allows
   communities to define private extensions to carry information unique
   to those communities.  Each extension in a certificate may be
   designated as critical or non-critical.  A certificate using system
   (an application validating a certificate) must reject the certificate
   if it encounters a critical extension it does not recognize.  A non-
   critical extension may be ignored if it is not recognized.  The
   following presents recommended extensions used within Internet
   certificates and standard locations for information.  Communities may
   elect to use additional extensions; however, caution should be
   exercised in adopting any critical extensions in certificates which
   might be used in a general context.

   The extensions referenced below are defined in detail in the X.509
   Amendment along with the specification of syntax and object
   identifiers.  Because the intent is to align exactly with those
   definitions, the material is not reproduced here.  The following
   sections describe Internet profiling decisions and Internet private
   extensions.

   << Once finalized, the certificate ASN.1 definition will be included
   in an appendix to this document. >>

4.2.1  Standard Extensions

4.2.1.1  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the particular public key used to sign a certificate.
   The identification can be based on either the key identifier (the
   subject key identifier in the issuer's certificate) or on the issuer
   name and serial number.  The key identifier method is recommended in
   this profile.  This extension would be used where an issuer has
   multiple signing keys (either due to multiple concurrent key pairs or
   due to changeover).  In general, this extension should be included in
   certificates.




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4.2.1.2  Subject Key Identifier

   The subject key identifier extension provides a means of identifying
   the particular public key used in an application.  Where a reference
   to a public key identifier is needed (as with an Authority Key
   Identifier) and one is not included in the associated certificate, a
   SHA-1 hash of the subject public key shall be used.  The hash shall
   be calculated over the value (excluding tag and length) of the
   subject public key field in the certificate.  This extension should
   be marked non-critical.

4.2.1.3  Key Usage

   The key usage extension defines the purpose (e.g., encipherment,
   signature, certificate signing) of the key contained in the
   certificate.  The usage restriction might be employed when a
   multipurpose key is to be restricted (e.g., when an RSA key should be
   used only for signing or only for key encipherment).  The profile
   recommends that when used, this be marked as a critical extension.

4.2.1.4  Private Key Usage Period

   This profile recommends against the use of this extension.  CA's
   conforming to this profile should not generate certificates with
   private key usage period extensions.

4.2.1.5  Certificate Policies

   The certificate policies extension contains a sequence of policy
   information terms, each of which consists of an object identifier
   (OID) and optional qualifiers.  These policy information terms
   indicate the policy under which the certificate has been issued and
   the purposes for which the certificate may be used.  This profile
   strongly recommends that a simple OID be present in this field.
   Optional qualifiers which may be present are expected to provide
   information about obtaining CA rules, not change the definition of
   the policy. Applications are expected to have a list of those
   policies which they will accept and to compare the policy OIDs in the
   certificate to that list.

   << Do we want to say anything about criticality? >>

4.2.1.6  Policy Mappings

   This extension may be supported by CAs and/or applications, and it is
   always non-critical.





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4.2.1.7  Subject Alternative Name

   The subject alternative names extension allows additional identities
   to be bound to the subject of the certificate.  Defined options
   include an rfc822 name (electronic mail address), a DNS name, an IP
   address, and a URI.  Other options exist, including completely local
   definitions.  Multiple instances of a name and multiple name forms
   may be included.  Whenever such identities are to be bound into a
   certificate, the subject alternative name (or issuer alternative
   name) extension shall be used.  (Note: a form of such an identifier
   may also be present in the subject distinguished name; however, the
   alternative name extension is the preferred location for finding such
   information.)  Further, if the only subject identity included in the
   certificate is an alternative name form (e.g., an electronic mail
   address), then the subject distinguished name should be empty (an
   empty sequence), the subjectAltName extension should be used, and the
   subjectAltName extension must be marked critical.

   << In the previous version we said: The use of otherName should not
   be used in conjunction with this profile.  Should we put this
   restriction back? >>

   Alternative names may be constrained in the same manner as subject
   distinguished names using the name constraints extension as described
   in section 4.2.1.11.

4.2.1.8  Issuer Alternative Name

   As with 4.2.1.7, this extension is used to associate Internet style
   identities with the certificate issuer.  If the only issuer identity
   included in the certificate is an alternative name form (e.g., an
   electronic mail address), then the issuer distinguished name should
   be empty (an empty sequence), the issuerAltName extension should be
   used, and the issuerAltName extension must be marked critical.

4.2.1.9  Subject Directory Attributes

   The subject directory attributes extension is not recommended as an
   essential part of this profile, but it may be used in local
   environments.  This extension is always non-critical.

4.2.1.10  Basic Constraints

   The basic constraints extension identifies whether the subject of the
   certificate is a CA and how deep a certification path may exist
   through that CA.  This profile requires the use of this extension,
   and it shall critical for all certificates issued to CAs.




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4.2.1.11  Name Constraints

   The name constraints extension provides permitted and excluded
   subtrees that place restrictions on names that may be included within
   a certificate issued by a given CA.  Restrictions may apply to the
   subject distringuished name or subject alternative names.  Any name
   matching a restriction in the excluded subtrees field is invalid
   regardless of information appearing in the permitted subtrees.
   Restrictions for the rfc822, dNSName, and uri name forms are all
   expressed in terms of strings with wild card matching.  An "*" is the
   wildcard character.  The minimum and maximum fields in general
   subtree are not used for these name forms. For uris and rfc822 names,
   the restriction applies to the host part of the name.  Examples would
   be foo.bar.com; www*.bar.com; *.xyz.com.

   << X.208 (1988) defines is IA5String as PrintableString plus
   NumericString plus SPACE and DELETE. Thus, it does not allow the for
   the * character.  What should we use instead? >>

4.2.1.12  Policy Constraints

   The policy constraints extension may be used by CAs.

4.2.1.13  CRL Distribution Points

   The CRL distribution points extension identifies how CRL information
   is obtained.  The profile recommends support for this extension by
   CAs and applications.  Further discussion of CRL management is
   contained in section 5.

4.2.2  Private Internet Extensions

4.2.2.1  Subject Information Access

   The name information in the certificate identifies the entity to
   which the public key is bound.  In some instances, it may also be
   necessary to know where to find additional information about the
   named entity.  In the case of X.500 names, this relationship is
   automatic.  The subject information access extension provides a means
   of identifying where and how to find information about the subject.
   The extension specifies a method of obtaining information and a
   general name form indicating where.  This extension should always be
   non-critical.

   subjectInfoAccess EXTENSION  ::=  {
        SYNTAX                SubjectInfoAccessSyntax
        IDENTIFIED BY         { TBD-OID-1 }  }




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   SubjectInfoAccessSyntax ::= SEQUENCE SIZE (1..MAX) OF AccessDescription

   AccessDescription  ::=  SEQUENCE  {
        accessMethod          OBJECT IDENTIFIER,
        accessLocation        GeneralName  }

   << What upper bound should be assigned for MAX? >>

   << Where is the list of access method OIDs going to be specified? >>

4.2.2.2  Authority Information Access

   The authority information access extension indicates how to access CA
   information and services for the issuer of the certificate in which
   the extension appears.  Information and services include certificate
   status or on-line validation services, certificate retrieval, CA
   policy data, and CA certificates (certificates certifying the target
   CA to aid in certification path navigation).  This extension may be
   included in subject or CA certificates and may be critical or non-
   critical.

   << What does it mean to mark this extension critical? >>

   authorityInfoAccess EXTENSION  ::=  {
        SYNTAX                AuthorityInfoAccessSyntax
        IDENTIFIED BY         { TBD-OID-2 }  }

   AuthorityInfoAccessSyntax  ::=  SEQUENCE  {
        certStatus        [0] SEQUENCE OF AccessDescription,
        certRetrieval     [1] SEQUENCE OF AccessDescription,
        caPolicy          [2] SEQUENCE OF AccessDescription,
        caCerts           [3] SEQUENCE OF AccessDescription  }

4.2.2.3  CA Information Access

   The CA information access extension indicates how to access CA
   information and services for the subject of the certificate in which
   the extension appears.  Information and services include certificate
   status or on-line validation services, certificate retrieval, CA
   policy data, and CA certificates (certificates certifying the target
   CA to aid in cert path navigation).  This extension may be included
   only in CA certificates and may be critical or non-critical.  CA
   certificates may include both an authority and a caInfoAccess
   extension to describe access methods for both the CA and its issuer.

   caInfoAccess EXTENSION  ::=  {
        SYNTAX                CAInfoAccessSyntax
        IDENTIFIED BY         { TBD-OID-2 }  }



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   CAInfoAccessSyntax  ::=  SEQUENCE  {
        certStatus        [0] SEQUENCE OF AccessDescription,
        certRetrieval     [1] SEQUENCE OF AccessDescription,
        caPolicy          [2] SEQUENCE OF AccessDescription,
        caCerts           [3] SEQUENCE OF AccessDescription  }

4.3  Examples

   << Certificate samples including descriptive text and ASN.1 encoded
   blobs will be inserted. >>

5  CRL and CRL Extensions Profile

   As described above, one goal of this X.509 v2 CRL profile is to
   foster the creation of an interoperable and reusable Internet PKI.
   To achieve this goal, guidelines for the use of extensions are
   specified, and some assumptions are made about the nature of
   information included in the CRL.

   CRLs may be used in a wide range of applications and environments
   covering a broad spectrum of interoperability goals and an even
   broader spectrum of operational and assurance requirements.  This
   profile establishes a common baseline for generic applications
   requiring broad interoperability.  Emphasis is placed on support for
   X.509 v2 CRLs.  The profile defines a baseline set of information
   that can be expected in every CRL.  Also, the profile defines common
   locations within the CRL for frequently used attributes, and common
   representations for these attributes.

   This profile does not define any private Internet CRL extensions or
   CRL entry extensions.

   Environments with additional or special purpose requirements may
   build on this profile or may replace it.

5.1  CRL Fields

   The X.509 v2 CRL syntax is as follows.  For signature calculation,
   the data that is to be signed is ASN.1 DER encoded.  ASN.1 DER
   encoding is a tag, length, value encoding system for each element.

   CertificateList  ::=  SEQUENCE  {
        tbsCertList          TBSCertList,
        signatureAlgorithm   AlgorithmIdentifier,
        signature            BIT STRING  }

   TBSCertList  ::=  SEQUENCE  {
        version                 Version OPTIONAL,



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                                     -- if present, must be v2
        signature               AlgorithmIdentifier,
        issuer                  Name,
        thisUpdate              UTCTime,
        nextUpdate              UTCTime,
        revokedCertificates     SEQUENCE OF SEQUENCE  {
             userCertificate         CertificateSerialNumber,
             revocationDate          UTCTime,
             crlEntryExtensions      Extensions OPTIONAL  }  OPTIONAL,
        crlExtensions           [0]  Extensions OPTIONAL  }

   Version  ::= INTEGER  {  v1(0), v2(1), v3(2)  }

   AlgorithmIdentifier  ::=  SEQUENCE  {
        algorithm               OBJECT IDENTIFIER,
        parameters              ANY DEFINED BY algorithm OPTIONAL  }
                                     -- contains a value of the type
                                     -- registered for use with the
                                     -- algorithm object identifier value

   CertificateSerialNumber  ::=  INTEGER

   Extensions  ::=  SEQUENCE OF Extension

   Extension  ::=  SEQUENCE  {
        extnId                  OBJECT IDENTIFIER,
        critical                BOOLEAN DEFAULT FALSE,
        extnValue               OCTET STRING  }
                                     -- contains a DER encoding of a value
                                     -- of the type registered for use with
                                     -- the extnId object identifier value

   The following items describe the proposed use of the X.509 v2 CRL for
   in Internet PKI.

5.1.1  Version

   This field describes the version of the encoded CRL.  When extensions
   are used, as expected in this profile, use version 2 (the integer
   value is 1).  If neither CRL extensions nor CRL entry extensions are
   present, use version 1 (the integer value must be omitted).

5.1.2  Signature

   This field contains the algorithm identifier for the algorithm used
   to sign the CRL.  Section 7.2 lists the signature algorithms used in
   the Internet PKI.




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5.1.3  Issuer Name

   The issuer name identifies the entity who has signed (and issued the
   CRL).  The issuer identity may be carried in the issuer name field
   and/or the issuerAltName extension.  If identity information is
   present only in the issuerAltName extension, then the issuer name may
   be an empty sequence and the issuerAltName extension must be
   critical.

5.1.4  This Update

   This field indicates the issue date of this CRL..  It is strongly
   recommended that UTCTime values be expressed Greenwich Mean Time
   (Zulu) and not use seconds (i.e., times are YYMMDDHHMMZ).  If seconds
   are used, a value of 00 seconds should never be encoded.

5.1.5  Next Update

   This field indicates the date by which the next CRL will be issued.
   The next CRL could be issued before the indicated date, but it will
   not be issued any later than the indicated date.

   As described in the previous section, the UTCTime for Next Update
   should be expressed Greenwich Mean Time (Zulu) and not use seconds.

5.1.6  Revoked Certificates

   Revoked certificates are listed.  The revoked certificates are named
   by their serial numbers.  Certificates are uniquely identified by the
   combination of the issuer name or issuer alternative name along with
   the user certificate serial number.  The date on which the revocation
   occured is specified.  As described in section 5.1.4, the UTCTime for
   revocationDate should be expressed Greenwich Mean Time (Zulu) and not
   use seconds..  CRL entry extensions are discussed in section 5.3.

   When a CA wishes to revoke a certificate that it issued to another
   CA, the revocation shall appear on the CRL.  The revocation should
   also appear on the authority revocation list (ARL).  The CA is
   revoking a certificate that it issued.

5.2  CRL Extensions

   The extensions defined by ANSI X9 and ISO for X.509 v2 CRLs [X.509-
   AM] [X9.55] provide methods for associating additional attributes
   with CRLs.  The X.509 v2 CRL format also allows communities to define
   private extensions to carry information unique to those communities.
   Each extension in a CRL may be designated as critical or non-
   critical.  A CRL validation must fail if it encounters an critical



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   extension which it does not know how to process.  However, an
   unrecognized non-critical extension may be ignored. The following
   presents those extensions used within Internet CRLs.  Communities may
   elect to use additional extensions; however, caution should be
   exercised in adopting any critical extensions in CRLs which might be
   used in a general context.

5.2.1  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the particular public key used to sign a CRL.  The
   identification can be based on either the key identifier (the subject
   key identifier in the CRL signer's certificate) or on the issuer name
   and serial number.  The key identifier method is recommended in this
   profile.  This extension would be used where an issuer has multiple
   signing keys, either due to multiple concurrent key pairs or due to
   changeover.  In general, this non-critical extension should be
   included in certificates.

5.2.2  Issuer Alternative Name

   The issuer alternative names extension allows additional identities
   to be associated with the issuer of the CRL.  Defined options include
   an rfc822 name (electronic mail address), a DNS name, an IP address,
   and a URI.  Multiple instances of a name and multiple name forms may
   be included.  Whenever such identities are used, the issuere
   alternative name extension shall be used.  Further, if the only
   issuer identity included in the CRL is an alternative name form
   (e.g., an electronic mail address), then the issuer distinguished
   name should be empty (an empty sequence), the issuerAltName extension
   should be used, and the issuerAltName extension must be marked
   critical.

5.2.3  CRL Number

   The CRL number is a non-critical CRL extension which conveys a
   monotonically increacing sequence number for each CRL issued by a
   given CA through a specific CA X.500 Directory entry or CRL
   distribution point.  This extension allows users to easily determine
   when a particular CRL superceeds another CRL.  CAs conforming to this
   profile shall include this CRL.
5.2.4  Issuing Distribution Point

   The issuing distribution point is a critical CRL extension that
   identifies the CRL distribution point for a particular CRL, and it
   indicates whether the CRL covers revocation for end entity
   certificates only, CA certificates only, or a limitied set of reason
   codes.  Since this extension is critical, all certificate users must



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   be prepared to receive CRLs with this extension.

   The CRL is signed using the CA's private key.  CRL Distribution
   Points do not have their own key pairs.  If the CRL is stored in the
   X.500 Directory, it is stored in the Directory entry corresponding to
   the CRL distribution point, which may be different that the Directory
   entry of the CA.

   CRL distribution points, if used by a CA, should be partition the CRL
   on the basis of compromise and routine revocation.  That is, the
   revocations with reason code keyCompromise (1) shall appear in one
   distribution point, and the revocations with other reason codes shall
   appear in another distribution point.

5.2.5  Delta CRL Indicator

   The delta CRL indicator is a critical CRL extension that identifies a
   delta-CRL.  The use of delta-CRLs can significantly improve
   processing time for applications which store revocation information
   in a format other than the CRL structure.  This allows changes to be
   added to the local database while ignoring unchanged information that
   is already in the local databse.

   When a delta-CRL is issued, the CAs shall also issue a complete CRL.

   The value of BaseCRLNumber identifies the CRL number of the base CRL
   that was used as the starting point in the generation of this delta-
   CRL.  The delta-CRL contains the changes between the base CRL and the
   current CRL issued along with the delta-CRL.  It is the decision of a
   CA as to whether to provide delta-CRLs.  Again, a delta-CRL shall not
   be issued without a corresponding CRL.  The value of CRLNumber for
   both the delta-CRL and the corresponding CRL shall be identical.

   A CRL user constructing a locally held CRL from delta-CRLs shall
   consider the constructed CRL incomplete and unusable if the CRLNumber
   of the received delta-CRL is more that one greater that the CRLnumber
   of the delta-CRL last processed.
5.3  CRL Entry Extensions

   The CRL entry extensions already defined by ANSI X9 and ISO for X.509
   v2 CRLs [X.509-AM] [X9.55] provide methods for associating additional
   attributes with CRL entries.  The X.509 v2 CRL format also allows
   communities to define private CRL entry extensions to carry
   information unique to those communities.  Each extension in a CRL
   entry may be designated as critical or non-critical.  A CRL
   validation must fail if it encounters an critical CRL entry extension
   which it does not know how to process.  However, an unrecognized
   non-critical CRL entry extension may be ignored.  The following



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   presents recommended extensions used within Internet CRL entries and
   standard locations for information.  Communities may elect to use
   additional CRL entry extensions; however, caution should be exercised
   in adopting any critical extensions in CRL entries which might be
   used in a general context.

5.3.1  Reason Code

   The reasonCode is a non-critical CRL entry extension that identifies
   the reason for the certificate revocation. As are strongly encouraged
   to include reason codes in CRL entries; however, the reason code CRL
   entry extension should be absent instead of using the unspecified (0)
   reasonCode value.

5.3.2  Hold Instruction Code

   The hold instruction code is a non-critical CRL entry extension that
   provides a registered instruction identifier which indicates the
   action to be taken after encountering a certificate that has been
   placed on hold.

   << The Directory Specification does not define any standard hold
   instruction codes.  Where will they be defined?  Are any specific to
   the Internet environment? >>

5.3.3  Invalidity Date

   The invalidity date is a non-critical CRL entry extension that
   provides the date on which it is known or suspected that the private
   key was compromised or that the certificate otherwise became invalid.
   This date may be earlier than the revocation date in the CRL entry,
   but it must be later than the issue date of the previously issued
   CRL.  Remember that the revocation date in the CRL entry specifies
   the date that the CA revoked the certificate.  Whenever this
   information is available, CAs are strongly encouraged to share it
   with CRL users.

   The GeneralizedTime values included in this field shall be expressed
   in Greenwich Mean Time (Zulu) and omit trailing zeros in fractional
   seconds.  Normally, GeneralizedTime will be expressed as
   YYYYMMDDHHMMSSZ.
5.4  Examples

   << CRL samples including descriptive text and ASN.1 encoded blobs
   will be inserted. >>






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6  Certificate Path Validation

   << There used to be long section here that contained the
   certification path validation procedures.  The major deviations from
   the procedures outlined in [X.509-AM] were due to certificate hold
   processing.  These procedures are no longer onerous, so there is no
   reason to prohibit the use of the hold facility.  Does anyone see a
   reason to reatin this section? >>

7  Algorithm Support

7.1  One-way Hash Functions

   One-way hash functions are also called message digest algorithms.
   SHA-1 is be the most popular one-way hash function used in the
   Internet PKI.  However, PEM uses MD2 for certificates [RFC 1422] [RFC
   1423]. For this reason, MD2 is included in this profile.

7.1.1  MD2 One-way Hash Function

   MD2 was also developed by Ron Rivest, but RSA Data Security has not
   placed the MD2 algorithm in the public domain.  Rather, RSA Data
   Security has granted license to use MD2 for non-commerical Internet
   Privacy-Enhanced Mail.  For this reason, MD2 may continue to be used
   with PEM certificates, but SHA-1 is preferred.  MD2 is fully
   described in RFC 1319 [RFC 1319].

   At the Selected Areas in Cryptography '95 conference in May 1995,
   Rogier and Chauvaud presented an attack on MD2 that can nearly find
   collisions [RC95].  Collisions occur when two different messages
   generate the same message digest.  A checksum operation in MD2 is the
   only remaining obstacle to the success of the attack.  For this
   reason, the use of MD2 for new applications is discouraged.  It is
   still reasonable to use MD2 to verify existing signatures, as the
   ability to find collisions in MD2 does not enable an attacker to find
   new messages having a previously computed hash value.

   << More information on the attack and its implications can be
   obtained from a RSA Laboratories security bulletin.  These bulletins
   are available from <http://www.rsa.com/>. >>

7.1.2  SHA-1 One-way Hash Function

   SHA-1 was developed by the U.S. Government.  SHA-1 is fully described
   in FIPS 180-1 [FIPS 180-1].

   SHA-1 is the one-way hash function of choice for use with both RSA
   the DSA signature algorithms.



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7.2  Signature Algorithms

   RSA and DSA are the most popular signature algorithms used in the
   Internet.

   There is some ambiguity in 1988 X.509 document with respect to the
   definition of the SIGNED macro and the representation of a signature
   in a certificate or a CRL.  The interpretation selected for the
   Internet requires that the data to be signed (e.g., the one-way hash
   function output value) is first ASN.1 encoded as an OCTET STRING and
   the result is encrypted (e.g., using RSA Encryption) to form the
   signed quantity.  Asd part of the SIGNED macro, this signature value
   is then ASN.1 encoded as a BIT STRING.

7.2.1  RSA Signature Algorithm

   A patent statement regarding the RSA algorithm can be found at the
   end of this profile.

   The RSA algorithm is named for it's inventors: Rivest, Shamir, and
   Adleman.  The RSA signature algorithm is defined in PKCS #1 [PKCS#1].
   It combines either the MD2 or the SHA-1 one-way hash function with
   the RSA asymmetric encryption algorithm.  As defined in PKCS #1, the
   ASN.1 object identifiers used to identify these signature algorithms
   are:

        md2WithRSAEncryption OBJECT IDENTIFIER  ::=  {
            iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
            pkcs-1(1) 2  }

        sha-1WithRSAEncryption OBJECT IDENTIFIER  ::=  {
            iso(1) identified-organization(3) oiw(14) secsig(3)
            algorithm(2) 29  }

   When either of these object identifiers is used within the ASN.1 type
   AlgorithmIdentifier, the parameters component of that type shall the
   ASN.1 type NULL.

7.2.2  DSA Signature Algorithm

   A patent statement regarding the DSA can be found at the end of this
   profile.

   The Digital Signature Algorithm (DSA) is also called the Digital
   Signature Standard (DSS).  DSA was developed by the U.S. Government,
   and DSA is used in conjunction with the the SHA-1 one-way hash
   function.  DSA is fully described in FIPS 186 [FIPS 186].  The ASN.1
   object identifiers used to identify this signature algorithm is:



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        dsaWithSHA-1 OBJECT IDENTIFIER  ::=  {
            iso(1) identified-organization(3) oiw(14) secsig(3)
            algorithm(2) 27 }

   The DSA algorithm syntax includes optional parameters.  These
   parameters are commonly referred to as p, q, and g.  The
   AlgorithmIdentifier within subjectPublicKeyInfo is the only place
   within a certificate where these parameters shall be present.  If the
   DSA algorithm parameters are absent from the subjectPublicKeyInfo
   AlgorithmIdentifier and the CA signed the subject certificate using
   DSA, then the certificate issuer's DSA parameters apply to the
   subject's DSA key.  If the DSA algorithm parameters are absent from
   the subjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
   subject certificate using a signature algorithm other than DSA, then
   the subject's DSA parameters are distributed by other means.  The
   parameters are included using the following ASN.1 structure:

        Dss-Parms  ::=  SEQUENCE  {
            p             INTEGER,
            q             INTEGER,
            g             INTEGER  }

   When signing, DSA algorithm generates two values.  These values are
   commonly referred to as r and s.  To easily transfer these two values
   as one siganture, they are ASN.1 encoded using the following ASN.1
   structure:

        Dss-Sig-Value  ::=  SEQUENCE  {
            r             INTEGER,
            s             INTEGER  }

7.3  Subject Public Key Algorithms

   << Add a section that lists the public key algorithms that are
   supported by this profile.  Obviously, RSA, DSA, Diffie-Hellman, and
   KEA will be included.  Are there others? >>

   << Should a different algorithm identifier be assigned to RSA
   signature keys and RSA key management keys?  If so, there will be one
   subsection for each within this section.>>
References

   [FIPS 180-1]  Federal Information Processing Standards Publication
              (FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
              [Supersedes FIPS PUB 180 dated 11 May 1993.]

   [FIPS 186] Federal Information Processing Standards Publication
              (FIPS PUB) 186, Digital Signature Standard, 18 May 1994.



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   [PKCS#1]   PKCS #1: RSA Encryption Standard, Version 1.4, RSA Data
              Security, Inc., 3 June 1991.

   [RC95]     Rogier, N. and Chauvaud, P., "The compression function of
              MD2 is not collision free," Presented at Selected Areas in
              Cryptography '95, Carleton University, Ottawa, Canada,
              18-19 May 1995.

   [RFC 1319] Kaliski, B., "The MD2 Message-Digest Algorithm," RFC 1319,
              RSA Laboratories, April 1992.

   [RFC 1422] Kent, S.,  "Privacy Enhancement for Internet Electronic
              Mail: Part II: Certificate-Based Key Management," RFC
   1422,
              BBN Communications, February 1993.

   [RFC 1423] Balenson, D., "Privacy Enhancement for Internet Electronic
              Mail: Part III: Algorithms, Modes, and Identifiers,"
              RFC 1423, Trusted Information Systems, February 1993.

   [X.208]    << Do we want to reference the 1988 or 1993 version? >>

   [X.509-AM] << Need final reference >>

   [X9.55]    << Need final reference >>

Patent Statements

   The Internet PKI relies on the use of patented public key technology.
   The Internet Standards Process as defined in RFC 1310 requires a
   written statement from the Patent holder that a license will be made
   available to applicants under reasonable terms and conditions prior
   to approving a specification as a Proposed, Draft or Internet
   Standard.

   Patent statements for DSA, RSA, and Diffie-Hellman follow.  These
   statements have been supplied by the patent holders, not the authors
   of this profile.

   Digital Signature Algorithm (DSA)

      The U.S. Government holds patent 5,231,668 on the Digital
      Signature Algorithm (DSA), which has been incorporated into
      Federal Information Processing Standard (FIPS) 186.  The patent
      was issued on July 27, 1993.

      The National Institute of Standards and Technology (NIST) has a
      long tradition of supplying U.S. Government-developed techniques



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      to committees and working groups for inclusion into standards on a
      royalty-free basis.  NIST has made the DSA patent available
      royalty-free to users worldwide.

      Regarding patent infringement, FIPS 186 summarizes our position;
      the Department of Commerce is not aware of any patents that would
      be infringed by the DSA.  Questions regarding this matter may be
      directed to the Deputy Chief Counsel for NIST.

   RSA Signature and Encryption

      << Now that PKP has dissolved, a revised patent statement for RSA
      from RSADSI is needed. >>

   Diffie-Hellman Key Agreement

      << Now that PKP has dissolved, a revised patent statement for
      Diffie-Hellman from Cylink is needed. >>

   Obsolete PKP Patent Statement

      << This statement is included here until a replacement from RSADSI
      and Cylink can be obtained. >>

      The Massachusetts Institute of Technology and the Board of
      Trustees of the Leland Stanford Junior University have granted
      Public Key Partners (PKP) exclusive sub-licensing rights to the
      following patents issued in the United States, and all of their
      corresponding foreign patents:

         Cryptographic Apparatus and Method
         ("Diffie-Hellman")......................... No. 4,200,770

         Public Key Cryptographic Apparatus
         and Method ("Hellman-Merkle").............. No. 4,218,582

         Cryptographic Communications System and
         Method ("RSA")............................. No. 4,405,829

         Exponential Cryptographic Apparatus
         and Method ("Hellman-Pohlig").............. No. 4,424,414

      These patents are stated by PKP to cover all known methods of
      practicing the art of Public Key encryption, including the
      variations collectively known as El Gamal.

      Public Key Partners has provided written assurance to the Internet
      Society that parties will be able to obtain, under reasonable,



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      nondiscriminatory terms, the right to use the technology covered
      by these patents.  This assurance is documented in RFC 1170 titled
      "Public Key Standards and Licenses".  A copy of the written
      assurance dated April 20, 1990, may be obtained from the Internet
      Assigned Number Authority (IANA).

      The Internet Society, Internet Architecture Board, Internet
      Engineering Steering Group and the Corporation for National
      Research Initiatives take no position on the validity or scope of
      the patents and patent applications, nor on the appropriateness of
      the terms of the assurance.  The Internet Society and other groups
      mentioned above have not made any determination as to any other
      intellectual property rights which may apply to the practice of
      this standard.  Any further consideration of these matters is the
      user's own responsibility.

Security Considerations

   This entire memo is about security mechanisms.
Author Addresses:

   Russell Housley
   SPYRUS
   PO Box 1198
   Herndon, VA 22070
   USA
   housley@spyrus.com

   Warwick Ford
   Nortel Secure Networks
   PO Box 3511, Station C
   Ottawa, Ontario
   Canada KY 4H7
   wford@bnr.ca

   David Solo
   BBN
   150 CambridgePark Drive
   Cambridge, MA 02140
   USA
   solo@bbn.com










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