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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 2459

PKIX Working Group                                   R. Housley (SPYRUS)
Internet Draft                                        W. Ford (Verisign)
                                                          W. Polk (NIST)
                                                           D. Solo (BBN)
expires in six months                                      December 1996


                   Internet Public Key Infrastructure

               Part I:  X.509 Certificate and CRL Profile

                  <draft-ietf-pkix-ipki-part1-03.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.








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1  Executive Summary

   This specification is Part 1 of a four part standard for development
   of a Public Key Infrastructure for the Internet.  This specification
   is a standalone document; implementations of this standard may
   proceed before completion of parts two through four.

   This specification profiles the format and semantics of certificates
   and certificate revocation lists for the Internet PKI.  Procedures
   are described for processing of certification paths in the Internet
   environment.  Encoding rules are provided for popular cryptographic
   algorithms.  Finally, a comprehensive ASN.1 module is provided in the
   appendices for all data structure defined or referenced.

   The specification presents profiles of the X.509 version 3
   certificate and version 2 certificate revocation lists. The profiles
   include the identification of ISO and ANSI extensions which may be
   useful in the Internet PKI and definition of new extensions to meet
   the Internet's requirements. The profiles are presented in the 1988
   Abstract Syntax Notation One (ASN.1) rather than the 1993 syntax used
   in the ISO standards.

   This specification also includes path validation procedures.  These
   procedures are based upon the ISO definition, but incorporate the
   Internet defined extensions.  Implementations are required to derive
   the same results but are not required to use the specified
   procedures.

   Finally, the specification describes procedures for identification
   and encoding of public key materials and digital signatures.
   Implementations are not required to use any particular cryptographic
   algorithms.  However, conforming implementations which use the
   identified algorithms are required to identify and encode the public
   key materials and digital signatures as described.

   An Appendix is provided containing all ASN.1 structures defined or
   referenced within this specification.  As above, the material is
   presented in the 1988 Abstract Syntax Notation One (ASN.1) rather
   than the 1993 syntax.

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, and IPSEC, as well as others.  In order to relieve
   some of the obstacles to using X.509 certificates, this document



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   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.

   This profile does not assume the deployment of an X.500 Directory
   system.  The profile does not prohibit the use of an X.500 Directory,
   but other means of distributing certificates and certificate
   revocation lists (CRLs) are supported.

2.2  Acceptability Criteria

   The goal of the Internet Public Key Infrastructure (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.

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, WWW servers, and the key manager for IPSEC within a router.



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   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.

3  Overview of Approach

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






























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      +---+
      | 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 management 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
                entities.







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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
   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



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   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.

   RFC 1422 furthermore has a name subordination rule which requires
   that a CA can only issue certificates for entities whose names are



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   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 certification 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.






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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



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   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 profile 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.




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   (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

   This section presents a profile for public key certificates that will
   foster interoperability and a reusable public key infrastructure.



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   This section is based upon the X.509 V3 certificate format and the
   standard certificate extensions defined in the Amendment [X.509-AM].
   The ISO definitions use the 1993 version of ASN.1; while this
   document uses the older ASN.1 syntax, the encoded certificate and
   standard extensions are equivalent.  This section also defines
   private extensions required to support a public key infrastructure
   for the Internet community.

   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)  }




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   CertificateSerialNumber  ::=  INTEGER

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

   CertificateValidityDate ::= CHOICE {
        utcTime        UTCTime,
        generalTime    GeneralizedTime }

   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  Certificate Fields

   The Certificate is a SEQUENCE of three required fields. The fields
   are are described in detail in the following subsections

4.1.1.1  tbsCertificate

   The first field in the sequence is the tbsCertificate.  This is a
   itself a sequence, and contains the names of the subject and issuer,
   a public key associated with the subject an expiration date, and
   other associated information.  The fields of the basic tbsCertificate
   are described in detail in section 4.1.2; the tbscertificate may also
   include extensions which are described in section 4.2.

4.1.1.2  signatureAlgorithm

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

   This field should contain the same algorithm identifier as the field
   signature in the sequence tbsCertificate (see section 4.1.2.3)



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4.1.1.3  signature

   The signature field contains a digital signature computed upon the
   ASN.1 DER encoded TBSCertificate.  The ASN.1 DER encoded
   TBSCertificate is used as the input to a one-way hash function.  The
   one-way hash function output value is ASN.1 encoded as an OCTET
   STRING and the result is encrypted (e.g., using RSA Encryption) to
   form the signed quantity.  This signature value is then ASN.1 encoded
   as a BIT STRING and included in the Certificate's signature field.

   By generating this signature, a CA certifies the validity of the
   information in tbscertificate.  In particular, the CA certifies the
   binding between the public key material and the subject of the
   certificate.

4.1.2  TBSCertificate

   The sequence TBSCertificate is a sequence which contains information
   associated with the subject of the certificate and the CA who issued
   it.  Every TBSCertificate contains the names of the subject and
   issuer, a public key associated with the subject, an expiration date,
   a version number and a serial number; some will contain optional
   unique identifier fields.  The remainder of this section describes
   the syntax and semantics of these fields.  A TBSCertificate may also
   include extensions.  Extensions for the Internet PKI are described in
   Section 4.2.

4.1.2.1  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 must 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.






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4.1.2.2  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).

4.1.2.3  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.

4.1.2.4  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.

4.1.2.5  Validity

   This field indicates the dates on which the certificate becomes valid
   (notBefore) and on which the certificate ceases to be valid
   (notAfter).  Both notBefore and notAfter may be encoded as UTCTime or
   GeneralizedTime.

   CAs conforming to this profile shall not issue certificates where
   notAfter or notBefore is encoded as GeneralizedTime before the year
   2005. CAs conforming to this profile shall not issue certificates
   where notAfter or notBefore is encoded as UTCTime after the year
   2015.

4.1.2.5.1  UTCTime

   The universal time type, UTCTime, is a standard ASN.1 type intended
   for international applications where local time alone is not
   adequate. UTCTime specifies the year through the two low order digits
   and time is specified to the precision of one minute or one second.
   UTCTime includes either Z (for Zulu, or Greenwich Mean Time) or a
   time differential.

   For the purposes of this profile, UTCTime values shall be expressed
   Greenwich Mean Time (Zulu) and shall include< seconds (i.e., times
   are YYMMDDHHMMSSZ), even where the number of seconds is zero.
   Conforming systems shall interpret the year field (YY) as follows:



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      Where YY is greater than 50, the year shall be interpreted as
      19YY; and

      Where YY is less than or equal to 50, the year shall be
      interpreted as 20YY.

4.1.2.6  GeneralizedTime

   The generalized time type, GeneralizedTime, is a standard ASN.1 type
   for variable precision representation of time.  Optionally, the
   GeneralizedTime field can include a representation of the time
   differential between local and Greenwich Mean Time.

   For the purposes of this profile, GeneralizedTime values shall be
   expressed Greenwich Mean Time (Zulu) and shall include seconds (i.e.,
   times are YYYYMMDDHHMMSSZ), even where the number of seconds is zero.
   GeneralizedTime values shall not include fractional seconds.

4.1.2.6  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.

4.1.2.7  Subject Public Key Info

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

4.1.2.8  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
   reused and that Internet certificates not make use of unique
   identifiers.  CAs 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



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   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.

   Each extension includes an object identifier and an ASN.1 structure.
   When an extension appears in a certificate, the object identifier
   appears as the field extnID and the corresponding ASN.1 encoded
   structure is the value of the bit string extnValue.  Only one
   instance of a particular extension may appear in a particular
   certificate. For example, a certificate may contain only one
   authority key identifier extension (4.2.1.1).  An extension may also
   include the optional boolean critical; critical's default value is
   FALSE.  The text for each extension specifies the acceptable values
   for the critical field.

   Conforming CAs are required to support the Basic Constraints
   extension (Section 4.2.1.10).  If the CA issues certificates with an
   empty sequence for the subject field, the CA must support the
   altSubjectName extension.  If the CA issues certificates with an
   empty sequence for the issuer field, the CA must support the
   altIssuerName extension.  Support for the remaining extensions is
   optional. Conforming CAs may support extensions that are not
   identified within this specification; certificate issuers are
   cautioned that marking such extensions as critical may inhibit
   interoperability.

   At a minimum, applications conforming to this profile shall recognize
   extensions which shall or may be critical. These extensions are:  key
   usage (4.2.1.3), certificate policies (4.2.1.5), the alternative
   subject name (4.2.1.7), issuer alternative name (4.2.1.8), basic
   constraints (4.2.1.10), name constraints (4.2.1.11), policy
   constraints (4.2.1.12), authority information access (4.2.2.2), and
   CA information access (4.2.2.3).

   In addition, this profile recommends support for key identifiers
   (4.2.1.2 and 4.2.1.3) and CRL distribution points (4.2.1.13).





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4.2.1  Standard Extensions

   This section identifies standard certificate extensions defined in
   [X.509-AM] for use in the Internet Public Key Infrastructure.  Each
   extension is associated with an object identifier defined in [X.509-
   AM].  These object identifiers are members of the
   certificateExtension arc, which is defined by the following:

   certificateExtension  OBJECT IDENTIFIER ::=  {joint-iso-ccitt(2) ds(5) 29}
   id-ce                 OBJECT IDENTIFIER ::=  certificateExtension

   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.
   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.

   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. Conforming CAs that generate this extension shall
   include or omit both authorityCertIssuer and
   authorityCertSerialNumber. If authorityCertIssuer and
   authorityCertSerialNumber are omitted, the keyIdentifier field shall
   be present.

   This extension shall not be marked critical.

   id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 35 }

   AuthorityKeyIdentifier ::= SEQUENCE {
        keyIdentifier                   [0] KeyIdentifier               OPTIONAL,
        authorityCertIssuer             [1] GeneralNames                OPTIONAL,
        authorityCertSerialNumber       [2] CertificateSerialNumber     OPTIONAL
    }

   KeyIdentifier ::= OCTET STRING

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



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   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.

   id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }

   SubjectKeyIdentifier ::= KeyIdentifier

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.

   id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

   KeyUsage ::= BIT STRING {
        digitalSignature        (0),
        nonRepudiation          (1),
        keyEncipherment         (2),
        dataEncipherment        (3),
        keyAgreement            (4),
        keyCertSign             (5),
        cRLSign                 (6) }

4.2.1.4  Private Key Usage Period

   The private key usage period extension allows the certificate issuer
   to specify a different validty period for the private key than the
   certificate. This extension is intended for use with digital
   signature keys.  This extension consists of two optional components
   notBefore and notAfter.  The private key associated with the
   certificate should not be used to sign objects before or after the
   times specified by the two components, respectively. CAs conforming
   to this profile shall not generate certificates with private key
   usage period extensions unless at least one of the two components is
   present.

   This profile recommends against the use of this extension.  CAs
   conforming to this profile shall not generate certificates with
   critical private key usage period extensions.

   id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::=  { id-ce 16 }

   PrivateKeyUsagePeriod ::= SEQUENCE {



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        notBefore       [0]     GeneralizedTime OPTIONAL,
        notAfter        [1]     GeneralizedTime OPTIONAL }

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 with specific policy requirements 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.  If this extension is
   critical, the path validation software must be able to interpret this
   extension, or must reject the certificate.  (Applications are free to
   ignore the policy field, even if the extension is marked critical.)

   This specification defines two policy qualifiers types for use by
   certificate policy writers and certificate issuers at their own
   discretion. The quailfier types are the CPS Pointer qualifier, and
   the User Notice qualifier.

   The CPS Pointer qualifier contains a pointer to a Certification
   Practice Statement (CPS) published by the CA.  The pointer is in the
   form of a URI.

   The User Notice qualifier contains a text string that is to be
   displayed to a certificate user (including subscribers and relying
   parties) prior to the use of the certificate.  The text string may be
   an IA5String or a BMPString - a subset of the ISO 100646-1 multiple
   octet coded character set.  A CA may invoke a procedure that requires
   that the certficate user acknowledge that the applicable terms and
   conditions have been disclosed or accepted.

   id-ce-certificatePolicies OBJECT IDENTIFIER ::=  { id-ce 32 }

   certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

   PolicyInformation ::= SEQUENCE {
        policyIdentifier   CertPolicyId,
        policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                PolicyQualifierInfo OPTIONAL }




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   CertPolicyId ::= OBJECT IDENTIFIER

   PolicyQualifierInfo ::= SEQUENCE {
        policyQualifierId   PolicyQualifierId,
        qualifier           ANY DEFINED BY policyQualifierId }

   -- policyQualifierIds for Internet policy qualifiers

   id-pkix-cps      OBJECT IDENTIFIER ::=  { pkix 4 }
   id-pkix-unotice  OBJECT IDENTIFIER ::=  { pkix 5 }

   PolicyQualifierId ::= ENUMERATED { id-pkix-cps, id-pkix-unotice }

   Qualifier ::= CHOICE {
        cPSuri    CPSuri,
        userNotice     UserNotice }

   CPSuri ::= IA5String

   UserNotice ::= CHOICE {
     ia5String     IA5String,
     bmpString     ANY }

4.2.1.6  Policy Mappings

   This extension is used in CA certificates.  It lists pairs of
   obbjectidentifiers; each pair includes an issuerDomainPolicy and a
   subjectDomainPolicy. The pairing indicates the issuing CA considers
   its issuerDomainPolicy equivalent to the subject CA's
   subjectDomainPolicy.

   The issuing CA's users may accept an issuerDomainPolicy for certain
   applications. The policy mapping tells the issuing CA's users which
   policies associated with the subject CA are comparable to the policy
   they accept.

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

   id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }

   PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
        issuerDomainPolicy      CertPolicyId,
        subjectDomainPolicy     CertPolicyId }







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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. If the subject field
   contains an empty squence, the subjectAltName extension shall be
   marked critical.

   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.

   id-ce-subjectAltName OBJECT IDENTIFIER ::=  { id-ce 17 }

   SubjectAltName ::= GeneralNames

   GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

   GeneralName ::= CHOICE {
        otherName                       [0]     ANY,
        rfc822Name                      [1]     IA5String,
        dNSName                         [2]     IA5String,
        x400Address                     [3]     ORAddress,
        directoryName                   [4]     Name,
        ediPartyName                    [5]     EDIPartyName,
        uniformResourceIdentifier       [6]     IA5String,
        iPAddress                       [7]     OCTET STRING,
        registeredID                    [8]     OBJECT IDENTIFIER }

   EDIPartyName ::= SEQUENCE {
        nameAssigner            [0]     DirectoryString OPTIONAL,
        partyName               [1]     DirectoryString }






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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. If the issuer field is empty and more than one issuerAltName
   extension is included in the certificate, the issuerAltName extension
   shall be marked critical.

   id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }

   IssuerAltName ::= GeneralNames

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.

   id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }

   SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

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 be critical for all certificates issued to CAs.

   id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }

   BasicConstraints ::= SEQUENCE {
        cA                      BOOLEAN DEFAULT FALSE,
        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

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. This
   extension may be critical or non-critical.




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   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.

   Restrictions of the form directoryName shall be applied to the
   subject field in the certificate and to the subjectAltName extensions
   of type directoryName.  Restrictions of the form x400Address shall be
   applied to subjectAltName extensions of type x400Address.

   The syntax and semantics for name constraints for otherName,
   ediPartyName, and registeredID are not defined by this specification.

   id-ce-nameConstraints OBJECT IDENTIFIER ::=  { id-ce 30 }

   NameConstraints ::= SEQUENCE {
        permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
        excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

   GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

   GeneralSubtree ::= SEQUENCE {
        base                    GeneralName,
        minimum         [0]     BaseDistance DEFAULT 0,
        maximum         [1]     BaseDistance OPTIONAL }

   BaseDistance ::= INTEGER (0..MAX)

4.2.1.12  Policy Constraints

   The policy constraints extension can be used in certificates issued
   to CAs.  The policy constraints extension constrains path validation
   in two ways. It can be used to prohibit policy mapping or limit the
   set of poicies that can in subsequent certificates. This extension
   may be critical or non-critical.

   id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 34 }

   PolicyConstraints ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
        policySet                       [0] CertPolicySet OPTIONAL,
        requireExplicitPolicy           [1] SkipCerts OPTIONAL,
        inhibitPolicyMapping            [2] SkipCerts OPTIONAL }

   SkipCerts ::= INTEGER (0..MAX)

   CertPolicySet ::= SEQUENCE SIZE (1..MAX) OF CertPolicyId



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4.2.1.13  CRL Distribution Points

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

   id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::=  { id-ce 31 }

   cRLDistributionPoints ::= {
        CRLDistPointsSyntax }

   CRLDistPointsSyntax ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

   DistributionPoint ::= SEQUENCE {
        distributionPoint       [0]     DistributionPointName OPTIONAL,
        reasons                 [1]     ReasonFlags OPTIONAL,
        cRLIssuer               [2]     GeneralNames OPTIONAL }

   DistributionPointName ::= CHOICE {
        fullName                [0]     GeneralNames,
        nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

   ReasonFlags ::= BIT STRING {
        unused                  (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6) }

4.2.2  Private Internet Extensions

   This section defines new extensions for use in the Internet Public
   Key Infrastructure.  These extensions may be used to direct
   applications to additional information about the certificate's
   subject or issuer. This extension includes the type of information,
   where it is located, and a method for obtaining the information. The
   types of information include certificate status, CA policy
   information, and related certificates.

   The object identifiers associated with the private extensions are
   defined under the iso (1), org (3), dod (6), internet (1),
   security(5) or 1.3.6.1.5, branch of the name space.  These extensions
   make use of OIDs of the form {applTCPProtoID port}, which identify
   TCP-based protocols that don't have OIDs assigned by other means, to
   identify common methods for retrieving information.



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   The following ASN.1 defines object identifiers which may be used by
   applications that implement the private extensions; additional access
   methods may be used, but the semantics are undefined by this
   document.

   pkix  OBJECT IDENTIFIER ::= { iso(1) org(3) dod (6) internet (1)
                  security(5) pkix(?) }

   -- Object identifiers for ftp, http, smtp and ldap protocols

   applTCPProto OBJECT IDENTIFIER ::= { 1 3 6 1 2 1 27 4 }

   ftpID    OBJECT-IDENTIFIER ::= {applTCPProtoID 21}
   httpID   OBJECT-IDENTIFIER ::= {applTCPProtoID 80}
   smtpID   OBJECT-IDENTIFIER ::= {applTCPProtoID 25}
   ldapID   OBJECT-IDENTIFIER ::= {applTCPProtoID 389}

   -- Object identifier for the X.500 directory access protocol

   dap OBJECT-IDENTIFIER ::= { 2 5 3 1 }

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 shall always be
   non-critical.

   id-pkix-subjectInfoAccess OBJECT-IDENTIFIER ::= { pkix 1}

   -- subjectInfoAccess ::=  { SubjectInfoAccessSyntax }

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

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

   This specification defines the following values for accessMethod:
   ftpID, httpID, smtpID, ldapID, and dap. The accessMethod value
   indicates the protocol required to obtain the information. If
   accessMethod is ftpID, then the information must available through
   anonymous ftp.  If accessMethod is ftpID, httpID, smtpID, or ldapID,



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   then the accessLocation shall be a uniformResourceIndicator (i.e., a
   URI). The URI shall specify all information required to retrieve the
   information.  If accessMethod is dap, then the accessLocation shall
   be a directoryName.

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.

   id-pkix-authorityInfoAccess OBJECT-IDENTIFIER ::= { pkix 2}

   -- authorityInfoAccess ::=  { AuthorityInfoAccessSyntax  }

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

   If certStatus is present, each entry in that sequence describes a
   mechanism and location for

      on-line verification of the status of this certificate, or

      the CRL on which this certificate would appear if revoked.

   If certRetrieval is present, each entry in the sequence describes how
   to retrieve all current certificates whose subject is the issuer of
   the certificate in which this extension appears.

   If caPolicy is present, each entry in the sequence describes how to
   retrieve the policy that was in effect when this certificate was
   issued.

   If caCerts is present, each entry in the sequence describes a
   mechanism and location for retrieval of certificates the issuer has
   issued to other CAs.

   If the certStatus, certRetrieval, caPolicy, or caCerts sequence has
   more than one value, conforming applications are not required to
   process all the values. Successful processing of any one



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   AccessDescritpion shall be sufficient.  It is the responsibility of
   the certificate issuer to ensure all mechanisms provide the same
   information.

   The expected values for AccessDescription are the values defined in
   4.2.2.1. Processing rules for other values for accessMethod are not
   defined.

   If this extension is critical, applications are required to use the
   information in the certStatus field (if present) to check the
   revocation status of this certificate, the certRetrieval field (if
   present) to obtain the issuer's current certificates, and the caCerts
   field (if present) to obtain certificates issued by the subject to
   other CAs.

   There are no additional processing requirements for cAPolicy if the
   extension is marked as critical.

4.2.2.3  CA Information Access

   Where the subject of a certificate is a CA, the subjectInfoAccess
   extension may be insufficient.  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 is syntactically identical to
   authorityInfoAccess, but is identified by a different OID.  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.

   id-pkix-caInfoAccess OBJECT-IDENTIFIER ::= { pkix 3 }

   -- caInfoAccess ::=  { AuthorityInfoAccessSyntax  }

   If certStatus is present, each entry in that sequence describes a
   mechanism and location for

      on-line verification of the status of this certificate, or

      CRL issued by the subject of this certificate.

   If certRetrieval is present, each entry in the sequence describes how
   to retrieve all current certificates whose subject is the subject of
   the certificate in which this extension appears.



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   If caPolicy is present, each entry in the sequence describes how to
   retrieve the current policy tssociated with the subject of this
   certificate.

   If caCerts is present, each entry in the sequence describes a
   mechanism and location for retrieval of certificates the subject has
   issued to other CAs.

   If the certStatus, certRetrieval, caPolicy, or caCerts sequence has
   more than one value, conforming applications are not required to
   process all the values. Successful processing of any one
   AccessDescritpion shall be sufficient.  It is the responsibility of
   the certificate issuer to ensure all mechanisms provide the same
   information.

   The legal values for AccessDescription shall be as defined in
   4.2.2.1.

   If this extension is critical, applications are required to use the
   information in the certStatus field (if present) to check the
   revocation status of this certificate, the certRetrieval field (if
   present) to obtain the subject's other current certificates, and the
   caCerts field (if present) to obtain certificates issued by the
   subject to other CAs.

   There are no additional processing requirements for cAPolicy if the
   extension is marked as critical.

4.3  Examples

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

   4.3.1 Simple certificate, no extensions

   <<TBD>>

   4.3.2 Certificate with Private extensions

   <<TBD>>

   4.3.3 certificate with no subject DN

   <<TBD>>







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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.

   Conforming CAs are not required to issue CRLs if other revocation or
   status mechanisms are provided.  Conforming CAs that issue CRLs are
   required to issue version 2 CRLs.  Conforming applications are
   required to process version 1 and 2 certificates.

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,
                                     -- if present, must be v2
        signature               AlgorithmIdentifier,
        issuer                  Name,
        thisUpdate              ChoiceOfTime,
        nextUpdate              ChoiceOfTime,
        revokedCertificates     SEQUENCE OF SEQUENCE  {



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             userCertificate         CertificateSerialNumber,
             revocationDate          ChoiceOfTime,
             crlEntryExtensions      Extensions OPTIONAL
                                                 -- if present, must be v2
                                  }  OPTIONAL,
        crlExtensions           [0]  Extensions OPTIONAL
                                                 -- if present, must be v2
                                  }

   ChoiceOfTime ::= CHOICE {
        utcTime        UTCTime,
        generalTime    GeneralizedTime }

   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 in
   the Internet PKI.

5.1.1  CertificateList Fields

   The CertificateList is a SEQUENCE of three required fields. The
   fields are are described in detail in the following subsections

5.1.1.1  tbsCertList

   The first field in the sequence is the tbsCertList.  This is a itself
   a sequence, and is generally thought of as the X.509 CRL. It contains
   the names of the subject and issuer, a public key associated with the
   subject an expiration date, and other associated information.  The



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   fields of the basic tbsCertificate are described in detail in section
   4.1.2; the tbscertificate may also include extensions which are
   described in section 4.2.

5.1.1.2  signatureAlgorithm

   The signatureAlgorithm field contains the algorithm identifier for
   the algorithm used by the CA to sign the CertificateList.  Section
   7.2 lists the supported signature algorithms.

5.1.1.3  signature

   The signature field contains a digital signature computed upon the
   ASN.1 DER encoded TBSCertList.  The ASN.1 DER encoded  TBSCertificate
   is used as the input to a one-way hash function.  The one-way hash
   function output value is ASN.1 encoded as an OCTET STRING and the
   result is encrypted (e.g., using RSA Encryption) to form the signed
   quantity.  This signature value is then ASN.1 encoded as a BIT STRING
   and included in the Certificate's signature field.

5.1.2  Certificate List "To Be Signed"

   The certificate list to be signed, or tBSCertList, is a SEQUENCE of
   required and optional fields.  The required fields identify the CRL
   issuer, the algorithm used to sign the CRL, the date and time the CRL
   was issued, and the date and time by which the CA will issue the next
   CRL.

   Optional fields include lists of revoked certificates and CRL
   extensions.  The revoked certificate list is optional to support the
   special case where a CA has not revoked any unexpired certificates it
   has issued.  It is expected that nearly all CRLs issued in the
   Internet PKI will contain one or more lists of revoked certificates.
   Similarly, the profile requires conforming CAs to use of one CRL
   extension (CRL number) in all CRLs issued.

5.1.2.1  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, version 1 CRLs are recommended (e.g., the integer value
   should be omitted).

5.1.2.2  Signature

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



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   the Internet PKI.

5.1.2.3  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.

5.1.2.4  This Update

   This field indicates the issue date of this CRL. ThisUpdate may be
   encoded as UTCTime or GeneralizedTime.

   CAs conforming to this profile shall not issue CRLs where thisUpdate
   is encoded as GeneralizedTime before the year 2005. CAs conforming to
   this profile shall not issue CRLs where thisUpdate is encoded as
   UTCTime after the year 2015.

   Where encoded as UTCTime, thisUpdate shall be specified and
   interpreted as defined in Section 4.1.2.5.1.  Where encoded as
   GeneralizedTime, thisUpdate shall be specified and interpreted as
   defined in Section 4.1.2.5.2.

5.1.2.5  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. nextUpdate may be
   encoded as UTCTime or GeneralizedTime.

   CAs conforming to this profile shall not issue CRLs where nextUpdate
   is encoded as GeneralizedTime before the year 2005. CAs conforming to
   this profile shall not issue CRLs where nextUpdate is encoded as
   UTCTime after the year 2015.

   Where encoded as UTCTime, nextUpdate shall be specified and
   interpreted as defined in Section 4.1.2.5.1.  Where encoded as
   GeneralizedTime, nextUpdate shall be specified and interpreted as
   defined in Section 4.1.2.5.2.

5.1.2.6  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



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   the user certificate serial number.  The date on which the revocation
   occured is specified.  The time for revocationDate shall be expressed
   as described in section 5.1.2.4. Additional information may be
   supplied in CRL entry extensions; CRL entry extensions are discussed
   in section 5.3.

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
   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 include extensions in CRLs which are not defined in this
   specification. However, caution should be exercised in adopting any
   critical extensions in CRLs which might be used in a general context.

   Conforming CAs that issue CRLs are required to support the CRL number
   extension (5.2.3), and include it in all CRLs issued. Conforming
   applications are required to support the critical and optionally
   critical CRL extensions issuer alternative name (5.2.2), issuing
   distribution point (5.2.4) and delta CRL indicator (5.2.5).

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.

   The syntax for this CRL extension is defined in Section 4.2.1.1.

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 issuer



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   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. If more than one issuerAltName
   extension appears in the CRL and the issuer distinguished name is
   empty, exactly one issuerAltName extension must be marked critical.

   The object identifier and syntax for this CRL extension are defined
   in Section 4.2.1.8.

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 supercedes another CRL.  CAs conforming to this
   profile shall include this extension in all CRLs.

   id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

   cRLNumber ::= INTEGER (0..MAX)

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
   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.

   id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }



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   issuingDistributionPoint ::= SEQUENCE {
        distributionPoint       [0] DistributionPointName OPTIONAL,
        onlyContainsUserCerts   [1] BOOLEAN DEFAULT FALSE,
        onlyContainsCACerts     [2] BOOLEAN DEFAULT FALSE,
        onlySomeReasons         [3] ReasonFlags OPTIONAL,
        indirectCRL             [4] BOOLEAN DEFAULT FALSE }

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.

   id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

   deltaCRLIndicator ::= BaseCRLNumber

   BaseCRLNumber ::= CRLNumber

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 a 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.

   All CRL entry extensions are non-critical; support for these
   extensions is optional for conforming CAs and applications.  However,
   CAs that issue CRLs are strongly encouraged to include reason codes
   (5.3.1) whenever this information is available.

5.3.1  Reason Code

   The reasonCode is a non-critical CRL entry extension that identifies
   the reason for the certificate revocation. CAs 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.

   id-ce-cRLReason OBJECT IDENTIFIER ::= { id-ce 21 }

   -- reasonCode ::= { CRLReason }

   CRLReason ::= ENUMERATED {
        unspecified             (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6),
        removeFromCRL           (8) }

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.

   id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

   holdInstructionCode ::= OBJECT IDENTIFIER

   The following instruction codes have been defined.  Conforming applications
   that process this extension shall recognize the following instruction codes.

   holdInstruction    OBJECT IDENTIFIER ::=



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                          { iso(1) member-body(2) us(840) x9-57(10040) 2 }

   id-holdinstruction-none       OBJECT IDENTIFIER ::= {holdInstruction 1}
   id-holdinstruction-callissuer OBJECT IDENTIFIER ::= {holdInstruction 2}
   id-holdinstruction-reject     OBJECT IDENTIFIER ::= {holdInstruction 3}

   Conforming applications which encounter a id-holdinstruction-
   callissuer must call the certificate issuer or reject the
   certificate.  Conforming applications which encounter a id-
   holdinstruction-reject ID shall reject the transaction. id-
   holdinstruction-none is semantically equivalent to the absence of a
   holdInstructionCode.  Its use is strongly deprecated for the Internet
   PKI.

   <<Note: I didn't think id-holdinstruction-pickupToken was appropriate
   for the Internet PKI>>

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.  GeneralizedTime shall be expressed as YYYYMMDDHHMMSSZ.

   id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

   invalidityDate ::=  GeneralizedTime

5.4  Examples

   5.4.1 Empty CRL

   <<TBD>>

   5.4.2 CRL with entries, no extensions

   <<TBD>>

   5.4.3 CRL with extensions



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   <<TBD>>

6  Certificate Path Validation

   Certification path validation procedures for the Internet PKI are
   based on Section 12.4.3 of [X.509-AM].

   Certification path processing verifies the binding between the
   subject distinguished name and subject public key.  The basic
   constraints and policy constraints extensions facilitate automated,
   self-contained implementation of certification path processing logic.

   The following is an outline of a procedure for validating
   certification paths.  An implementation shall be functionally
   equivalent to the external behaviour resulting from this procedure.
   Any algorithm may be used by a particular implementation so long as
   it derives the correct result.

   The inputs to the certification path processing procedure are:

      (a)  a set of certificates comprising a certification path;

      (b)  a CA name and trusted public key value (or an identifier of
      such a key if the key is stored internally to the certification
      path processing module) for use in verifying the first certificate
      in the certification path;


      (c)  a set of initial-policy identifiers (each comprising a
      sequence of policy element identifiers), which identifies one or
      more certificate policies, any one of which would be acceptable
      for the purposes of certification path processing; and

      (d)  the current date/time (if not available internally to the
      certification path processing module).

   The outputs of the procedure are:

      (a)  an indication of success or failure of certification path
      validation;

      (b)  if validation failed, a reason for failure; and

      (c)  if validation was successful, a (possibly empty) set of
      policy qualifiers obtained from CAs on the path.

   The procedure makes use of the following set of state variables:




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      (a)  acceptable policy set:  A set of certificate policy
      identifiers comprising the policy or policies recognized by the
      public key user together with policies deemed equivalent through
      policy mapping;

      (b)  constrained subtrees:  A set of root names defining a set of
      subtrees within which all subject names in subsequent certificates
      in the certification path shall fall; if no restriction is in
      force this state variable takes the special value unbounded; and

      (c)  excluded subtrees:  A set of root names defining a set of
      subtrees within which no subject name in subsequent certificates
      in the certification path may fall; if no restriction is in force
      this state variable takes the special value empty.

      The procedure involves an initialization step, followed by a
      series of certificate-processing steps.  The initialization step
      comprises:

      (a)  Initialize the constrained subtress to unbounded;

      (b)  Initialize the excluded subtrees indicator to empty; and

      (c)  Initialize the acceptable policy set to the set of initial-
      policy identifiers.

   Each certificate is then processed in turn, starting with the
   certificate signed using the trusted CA public key which was input to
   this procedure.  The last certificate is processed as an end-entity
   certificate; all other certificates (if any) are processed as CA-
   certificates.

   The following checks are applied to all certificates:

      (a)  Check that the signature verifies, that dates are valid, that
      the subject and issuer names chain correctly, and that the
      certificate has not been revoked;

      If the certificate has an empty sequence in the name field, name
      chaining will use the critical altSubjectNames and altIssuerNames
      fields. If the certificate has a critical authorityInfoAccess or
      caInfoAccess extension, the information in that extension must be
      used to determine the status of the certificates.

      (b)  If a key usage restriction extension is present in the
      certificate and contains a certPolicySet component, check that at
      least one member of the acceptable policy set appears in the
      field;



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      (c)  Check that the subject name or critical AltSubjectName
      extension is consistent with the constrained subtrees state
      variables; and

      (d)  Check that the subject name or critical AltSubjectName
      extension is consistent with the excluded subtrees state
      variables.

   If any one of the above checks fails, the procedure terminates,
   returning a failure indication and an appropriate reason.  If none of
   the above checks fail on the end-entity certificate, the procedure
   terminates, returning a success indication together with the set of
   all policy qualifier values encountered in the set of certificates.

   For a CA-certificate, the following constraint recording actions are
   then performed, in order to correctly set up the state variables for
   the processing of the next certificate:

      (a)  If permittedSubtrees is present in the certificate, set the
      constrained subtrees state variable to the intersection of its
      previous value and the value indicated in the extension field.

      (b)  If excludedSubtrees is present in the certificate, set the
      excluded subtrees state variable to the union of its previous
      value and the value indicated in the extension field.

      Note:  It is possible to specify an extended version of the above
      certification path processing procedure which results in default
      behaviour identical to the rules of Privacy Enhanced Mail [RFC
      1422].  In this extended version, additional inputs to the
      procedure are a list of one or more Policy Certification Authority
      (PCA) names and an indicator of the position in the certification
      path where the PCA is expected.  At the nominated PCA position,
      the CA name is compared against this list.  If a recognized PCA
      name is found, then a constraint of SubordinateToCA is implicitly
      assumed for the remainder of the certification path and processing
      continues.  If no valid PCA name is found, and if the
      certification path cannot be validated on the basis of identified
      policies, then the certification path is considered invalid.

7  Algorithm Support

   This section describes cryptographic alogrithms which may be used
   with this standard.  The section describes one-way hash functions and
   digital signature algorithms which may be used to sign certificates
   and CRLs, and identifies object identifiers for public keys contained
   in a certificate.




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   Conforming CAs and applications are not required to support the
   algorithms or algorithm identifiers described in this section.
   However, this profile requires conforming CAs and applications to
   conform when they use the algorithms identified here.

7.1  One-way Hash Functions

   This section identifies one-way hash functions for use in the
   Internet PKI.  One-way hash functions are also called message digest
   algorithms. SHA-1 is the preferred one-way hash function for 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 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 the
   RSA and DSA signature algorithms.

7.2  Signature Algorithms

   Certificates and CRLs described by this standard may be signed with
   any public key signature algorithm.  The certificate or CRL indicates



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   the algorithm through an algorithmidentifier which appears in the
   signatureAlgorithm field in a Certificate or CertificateList.  This
   algorithmidentfier is an OID and has optionally associated
   parameters.  This section identifies algorithm identifiers and
   parameters that shall be used in the signatureAlgorithm field in a
   Certificate or CertificateList.

   RSA and DSA are the most popular signature algorithms used in the
   Internet.  Signature algorithms are always used in conjunction with a
   one-way hash function identified in Section 7.1.

   The signature algorithm (and one-way hash function) used to sign a
   certificate or CRL is indicated by use of an algorithm identifier.
   An algorithm identifier is an object identifier, and may include
   associated parameters.  This section identifies OIDS for RSA and DSA
   and the corresponding parameters.

   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.  This
   signature value is then ASN.1 encoded as a BIT STRING and included in
   the Certificate or CertificateList (in the signature field).

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 combines either the MD2 or the
   SHA-1 one-way hash function with the RSA asymmetric encryption
   algorithm.  The RSA signature algorithm with MD2 and the RSA
   encryption algorithm is defined in PKCS #1 [PKCS#1].  As defined in
   PKCS #1, the ASN.1 object identifier used to identify this signature
   algorithm is:

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

   The RSA signature algorithm with SHA-1 and the RSA encryption
   algorithm is defined in by the OSI Ineroperability Workshop in []. As
   defined in [OIW], the ASN.1 object identifier used to identify this
   signature algorithm is:

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



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

   When signing, the RSA algorithm generates an integer y.  This value
   is converted to a bit string such that the most significant bit in y
   is the first bit in the bit string and the least significant bit in y
   is the last bit in the bit string.

   (In general this occurs in two steps.  The integer y is converted to
   an octect string such that the first octect has the most significance
   and the last octect has the least significance. The octet string is
   converted into a bit string such that the most significant bit of the
   first octect shall become the first bit in the bit string, and the
   least significant bit of the last octect is the last bit in the BIT
   STRING.

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 are:

           id-dsa-with-sha1 ID  ::=  {
                   iso(1) member-body(2) us(840) x9-57 (10040) secsig(2)
                   x9algorithm(4) 3 }

   The id-dsa-with-sha1 algorithm syntax has NULL parameters. The DSA
   parameters in the subjectPublicKeyInfo field of the certificate of
   the issuer shall apply to the verification of the signature.

   If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
   parameters and the CA signed the subject certificate using DSA, then
   the certificate issuer's parameters apply to the subject's DSA key.
   If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
   parameters and the CA signed the subject with a signature algorithm
   other than DSA, then clients shall not validate the certificate.

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




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

7.3  Subject Public Key Algorithms

   Certificates described by this standard may convey a public key for
   any public key algorithm. The certificate indicates the algorithm
   through an algorithmidentifier.  This algorithmidentfieier is an OID
   and optionally associated parameters.

   This section identifies preferred OIDs and parameters for the RSA,
   DSA, KEA, and Diffie-Hellman algorithms.  Conforming CAs shall use
   the identified OIDs when issuing certificates containing public keys
   for these algorithms. Conforming applications supporting any of these
   algorithms shall, at a minimum, recognize the OID identified in this
   section.

7.3.1 RSA  Keys

   The object identifier rsaEncryption identifies RSA public keys.

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

        rsaEncryption OBJECT IDENTIFIER ::=  { pkcs-1 1}

   The rsaEncryption object identifier is intended to be used in the
   algorithm field of a value of type AlgorithmIdentifier. The
   parameters field shall have ASN.1 type NULL for this algorithm
   identifier.

   The rsa public key shall be encoded using the ASN.1 type
   RSAPublicKey:

      RSAPublicKey ::= SEQUENCE {
         modulus       INTEGER, -- n
         publicExponent     INTEGER  -- e
                             }

   where modulus is the modulus n, and publicExponent is the public
   exponent e.  The DER encoded RSAPublicKey is  the value of the BIT
   STRING subjectPubliKey.

   This object identifier is used in public key certificates for both
   RSA signature keys and RSA encryption keys. The intended application
   for the key may be indicated in the key usage field (see Section
   4.2.1.3).  The use of a single key for both signature and encryption



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   purposes is not recommended, but is not forbidden.

7.3.2 Diffie-Hellman Key Exchange Key

   This diffie-hellman object identifier supported by this standard is
   defined by ANSI X9.42.

        dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) member-body(2)
                  US(840) ansi-x942(10046) number-type(2) 1 }

        DHParameter ::= SEQUENCE {
             prime INTEGER, -- p
             base INTEGER, -- g }

   The dhpublicnumber object identifier is intended to be used in the
   algorithm field of a value of type AlgorithmIdentifier. The
   parameters field of that type, which has the algorithm-specific
   syntax ANY DEFINED BY algorithm, would have ASN.1 type DHParameter
   for this algorithm.

        DHParameter ::= SEQUENCE {
          prime INTEGER, -- p
          base INTEGER, -- g }

   The fields of type DHParameter have the following meanings:

      prime is the prime p.

      base is the base g.

   The Diffie-Hellman public key (an INTEGER) is mapped to a
   subjectPublicKey (a BIT STRING) as follows: the most significant bit
   (MSB) of the INTEGER becomes the MSB of the BIT STRING; the least
   significant bit (LSB) of the INTEGER becomes the LSB of the BIT
   STRING.

7.3.3 DSA Signature Keys

   The object identifier supported by this standard is

        id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040)
                  secsig(2) x9algorithm(4) 1 }

   The id-dsa algorithm syntax includes optional parameters.  These
   parameters are commonly referred to as p, q, and g.  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



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   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  }

   If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
   parameters and the CA signed the subject certificate using DSA, then
   the certificate issuer's parameters apply to the subject's DSA key.
   If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
   parameters and the CA signed the subject with a signature algorithm
   other than DSA, then clients shall not validate the certificate.

   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 signature, they are ASN.1 encoded using the following ASN.1
   structure:

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

   The encoded signature is conveyed as the value of the BIT STRING
   signature in a Certificate or CertificateList.

   The DSA public key shall be ASN.1 encoded as an INTEGER; this
   encoding shall be used as the contents (i.e., the value) of the
   subjectPublicKey component (a BIT STRING) of the SubjectPublicKeyInfo
   data element.

        DSAPublicKey ::= INTEGER -- public key Y

7.3.4 Key Exchange Algorithm (KEA)

   The Key Exchange Algorithm (KEA) is a classified algorithm for
   exchanging keys.  A KEA "pairwise key" may be generated between two
   users if their KEA public keys were generated with the same KEA
   parameters.  The KEA parameters are not included in a certificate;
   instead a "domain identifier" is supplied in the parameters field.

   When the subjectPublicKeyInfo field contains a KEA key, the algorithm
   identifier and parameters shall be as defined in [sdn.701r]:




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      id-keyEncryptionAlgorithm  OBJECT IDENTIFIER   ::=
             { 2 16 840 1 101 2 1 1 22 }

      KEA-Parms-Id     ::= OCTET STRING


   The Kea-Parms-Id shall always appear when the subjectPublicKeyInfo
   field algorithm identifier is id-keyEncryptionAlgorithm. Kea-Parms-Id
   is the "domain identifier" and is ten octets in length. If the Kea-
   Parms-Id of two KEA keys are equivalent, the subjects possess the
   same KEA parameter values and may exchange keys.

   <<Need encoding of KEA key>>


8. ASN.1 Structures and OIDs


   PKIX1 DEFINITIONS ::=

   BEGIN


   -- need ASN.1 for:
   -- AlgorithmIdentifier
   -- ORAddress


   -- attribute data types --

   Attribute       ::=     SEQUENCE {
           type    AttributeValue,
           values  SET OF AttributeValue
                   -- at least one value is required -- }

   AttributeType           ::=     OBJECT IDENTIFIER

   AttributeValue          ::=     ANY

   AttributeTypeAndValue           ::=     SEQUENCE {
           type    AttributeValue,
           value   AttributeValue }

   AttributeValueAssertion ::=     SEQUENCE {AttributeType, AttributeValue}

   -- naming data types --

   Name            ::=     CHOICE { -- only one possibility for now --



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                                                   rdnSequence  RDNSequence }

   RDNSequence     ::=     SEQUENCE OF RelativeDistinguishedName

   DistinguishedName       ::=     RDNSequence

   RelativeDistinguishedName  ::=  SET SIZE (1 .. MAX) OF AttributeTypeAndValue

   -- Directory string type --

   DirectoryString ::= CHOICE {
           teletexString           TeletexString (SIZE (1..maxSize)),
           printableString         PrintableString (SIZE (1..maxSize)),
           universalString         ANY -- the '93 ASN.1 type UniversalString
                                                }

   -- basic stuff starts here

   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)  }

   CertificateSerialNumber  ::=  INTEGER

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

   CertificateValidityDate ::= CHOICE {



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        utcTime        UTCTime,
        generalTime    GeneralizedTime }

   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  }

   -- Extension ::= { {id-ce 15}, ... , keyUsage }

   ID                  ::=  OBJECT IDENTIFIER
   joint-iso-ccitt     ID   ::=  { 2 }
   ds             ID   ::=  {joint-iso-ccitt 5}
   certificateExtension  ID ::=  {ds 29}
   -- id-ce          ID   ::=  certificateExtension
   id-ce          ID   ::= {ds 29}

   AuthorityKeyIdentifier ::= SEQUENCE {
         keyIdentifier                   [0] KeyIdentifier               OPTIONAL,
         authorityCertIssuer             [1] GeneralNames                OPTIONAL,
         authorityCertSerialNumber       [2] CertificateSerialNumber     OPTIONAL
     }
          ( WITH COMPONENTS       {..., authorityCertIssuer PRESENT,
                                          authorityCertSerialNumber PRESENT} |
           WITH COMPONENTS        {..., authorityCertIssuer ABSENT,
                                          authorityCertSerialNumber ABSENT} )

   -- authorityKeyIdentifier ::= AuthorityKeyIdentifier

   KeyIdentifier ::= OCTET STRING

   -- subjectKeyIdentifier ::= KeyIdentifier

   KeyUsage ::= BIT STRING {
        digitalSignature        (0),
        nonRepudiation          (1),
        keyEncipherment         (2),
        dataEncipherment        (3),
        keyAgreement            (4),
        keyCertSign             (5),



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        cRLSign                 (6) }

   id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::=  { id-ce 16 }

   PrivateKeyUsagePeriod ::= SEQUENCE {
        notBefore       [0]     GeneralizedTime OPTIONAL,
        notAfter        [1]     GeneralizedTime OPTIONAL }
        ( WITH COMPONENTS       {..., notBefore PRESENT} |
        WITH COMPONENTS         {..., notAfter PRESENT} )

   id-ce-certificatePolicies OBJECT IDENTIFIER ::=  { id-ce 32 }

   CertificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

   PolicyInformation ::= SEQUENCE {
        policyIdentifier   CertPolicyId,
        policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                PolicyQualifierInfo OPTIONAL }

   CertPolicyId ::= OBJECT IDENTIFIER

   -- PolicyQualifierInfo ::= SEQUENCE {
   --       policyQualifierId  CERT-POLICY-QUALIFIER.&id
   --                                ({SupportedPolicyQualifiers}),
   --       qualifier          CERT-POLICY-QUALIFIER.&Qualifier
   --
   -- ({SupportedPolicyQualifiers}{@policyQualifierId})
   --                                         OPTIONAL }

   -- SupportedPolicyQualifiers CERT-POLICY-QUALIFIER ::= { ... }

   PolicyQualifierInfo ::= SEQUENCE {
          policyQualifierId  PolicyQualifierId,
          qualifier        ANY DEFINED BY policyQualifierId }

   PolicyQualifierId ::= ENUMERATED {
           qualId1 (1), qualId2 (2), qualId3 (3), qualId4 (4), qualId5 ( 5 ) }

   id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }

   PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
        issuerDomainPolicy      CertPolicyId,
        subjectDomainPolicy     CertPolicyId }

   id-ce-subjectAltName OBJECT IDENTIFIER ::=  { id-ce 17 }

   SubjectAltName ::= GeneralNames




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   GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

   GeneralName ::= CHOICE {
        otherName                       [0]     ANY,
        rfc822Name                      [1]     IA5String,
        dNSName                         [2]     IA5String,
        x400Address                     [3]     ORAddress,
        directoryName                   [4]     Name,
        ediPartyName                    [5]     EDIPartyName,
        uniformResourceIdentifier       [6]     IA5String,
        iPAddress                       [7]     OCTET STRING,
        registeredID                    [8]     OBJECT IDENTIFIER }

   -- OTHER-NAME ::= TYPE-IDENTIFIER  note: not supported in '88 ASN.1
   --              substituted ANY where used [GeneralName otherName]

   EDIPartyName ::= SEQUENCE {
        nameAssigner            [0]     DirectoryString OPTIONAL,
        partyName               [1]     DirectoryString }

   id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }

   IssuerAltName ::= GeneralNames

   id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }

   SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

   id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }

   BasicConstraints ::= SEQUENCE {
        cA                      BOOLEAN DEFAULT FALSE,
        pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

   id-ce-nameConstraints OBJECT IDENTIFIER ::=  { id-ce 30 }

   NameConstraints ::= SEQUENCE {
        permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
        excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

   GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

   GeneralSubtree ::= SEQUENCE {
        base                    GeneralName,
        minimum         [0]     BaseDistance DEFAULT 0,
        maximum         [1]     BaseDistance OPTIONAL }

   BaseDistance ::= INTEGER (0..MAX)



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   id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 34 }

   PolicyConstraints ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
        policySet                       [0] CertPolicySet OPTIONAL,
        requireExplicitPolicy           [1] SkipCerts OPTIONAL,
        inhibitPolicyMapping            [2] SkipCerts OPTIONAL }

   SkipCerts ::= INTEGER (0..MAX)

   CertPolicySet ::= SEQUENCE SIZE (1..MAX) OF CertPolicyId

   -- cRLDistributionPoints CRLDistPointsSyntax ::=
   --              SEQUENCE SIZE (1..MAX) OF DistributionPoint

   CRLDistPointsSyntax ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

   DistributionPoint ::= SEQUENCE {
        distributionPoint       [0]     DistributionPointName OPTIONAL,
        reasons                 [1]     ReasonFlags OPTIONAL,
        cRLIssuer               [2]     GeneralNames OPTIONAL }

   DistributionPointName ::= CHOICE {
        fullName                [0]     GeneralNames,
        nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

   ReasonFlags ::= BIT STRING {
        unused                  (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6) }

   pkix  OBJECT IDENTIFIER ::= { 1 3 6 1 5 3 }

   -- Object identifiers for ftp, http, smtp and ldap protocols

   applTCPProto OBJECT IDENTIFIER ::= { 1 3 6 1 2 1 27 4 }

   ftpID    OBJECT-IDENTIFIER ::= {applTCPProtoID 21}
   httpID   OBJECT-IDENTIFIER ::= {applTCPProtoID 80}
   smtpID   OBJECT-IDENTIFIER ::= {applTCPProtoID 25}
   ldapID   OBJECT-IDENTIFIER ::= {applTCPProtoID 389}

   -- Object identifier for the X.500 directory access protocol

   dap OBJECT-IDENTIFIER ::= { 2 5 3 1 }



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   id-pkix-subjectInfoAccess OBJECT IDENTIFIER ::= { pkix 1 }

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

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

   id-pkix-authorityInfoAccess OBJECT IDENTIFIER ::= { pkix 2 }

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

   id-pkix-caInfoAccess OBJECT-IDENTIFIER ::= { pkix 3 }

   -- caInfoAccess ::=  {
   --     AuthorityInfoAccessSyntax  }

   -- CRL structures

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

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




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   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

   ChoiceOfTime ::= CHOICE {
        utcTime        UTCTime,
        generalTime    GeneralizedTime }

   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

   id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

   CRLNumber ::= INTEGER (0..MAX)

   id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

   IssuingDistributionPoint ::= SEQUENCE {
        distributionPoint       [0] DistributionPointName OPTIONAL,
        onlyContainsUserCerts   [1] BOOLEAN DEFAULT FALSE,
        onlyContainsCACerts     [2] BOOLEAN DEFAULT FALSE,
        onlySomeReasons         [3] ReasonFlags OPTIONAL,
        indirectCRL             [4] BOOLEAN DEFAULT FALSE }


   id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

   -- deltaCRLIndicator ::= BaseCRLNumber

   BaseCRLNumber ::= CRLNumber

   id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

   -- reasonCode EXTENSION ::= {



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   --      SYNTAX  CRLReason
   --      IDENTIFIED BY { id-ce 21 } }

   CRLReason ::= ENUMERATED {
        unspecified             (0),
        keyCompromise           (1),
        cACompromise            (2),
        affiliationChanged      (3),
        superseded              (4),
        cessationOfOperation    (5),
        certificateHold         (6),
        removeFromCRL           (8) }

   id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

   HoldInstructionCode ::= OBJECT IDENTIFIER

   member-body ID ::= { iso 2 }
   us ID ::= { member-body 840 }
   x9cm ID ::= { us 10040 }
   holdInstruction ID ::= {x9cm 2}

   id-holdinstruction-none ID ::= {holdInstruction 1}
   id-holdinstruction-callissuer ID ::= {holdInstruction 2}
   id-holdinstruction-reject ID ::= {holdInstruction 3}

   id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

   InvalidityDate ::=  GeneralizedTime

   -- Algorithm strustures

        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  }

           id-dsa-with-sha1 ID  ::=  {
                   iso(1) member-body(2) us(840) x9-57 (10040) secsig(2)
                   x9algorithm(4) 3 }

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



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

        rsaEncryption OBJECT IDENTIFIER ::=  { pkcs-1 1}

        dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) member-body(2)
                  US(840) ansi-x942(10046) 1 }

        DHParameter ::= SEQUENCE {
             prime INTEGER, -- p
             base INTEGER -- g
                   }

        id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040)
                  secsig(2) x9algorithm(4) 1 }

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

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

      id-keyEncryptionAlgorithm  OBJECT IDENTIFIER   ::=
             { 2 16 840 1 101 2 1 1 22 }

      KEA-Parms-Id     ::= OCTET STRING

   id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 35 }
   id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }
   id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }
   id-pkix-policy-CPS OBJECT IDENTIFIER ::= { pkix 4 }

   CPSuri ::= IA5String

   id-pkix-policy-userNotice OBJECT IDENTIFIER ::= { pkix 5 }

   UserNotice ::= CHOICE {
     ia5String     IA5String,
     bnpString     ANY -- defined as BMPString in '93 ASN.1
                           }

   END

   References




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   [X9.57]    ANSI X9.57

   [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.

   [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.

   [RFC 1959] T. Howes, M. Smith, "An LDAP URL Format", RFC 1959,
              June 1996.

   [SDN.701R] SDN.701, "Message Security Protocol", Revision 4.0
              1996-06-07 with "Corrections to Message Security Protocol,
           SDN.701, Rev 4.0, 96-06-07." August 30, 1996.

   [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



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   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
      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




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INTERNET DRAFT                                             December 1996


         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,
      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 20172
   USA
   housley@spyrus.com

   Warwick Ford
   VeriSign, Inc.
   One Alewife Center
   Cambridge, MA 02140
   wford@verisign.com



Housley, Ford, Polk, & Solo                                    [Page 60]


INTERNET DRAFT                                             December 1996


   Tim Polk
   NIST
   Building 820, Room 426
   Gaithersburg, MD 20899
   wpolk@nist.gov

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







































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