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RFC 3280 - Internet X.509 Public Key Infrastructure Certificate


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Network Working Group                                         R. Housley
Request for Comments: 3280                              RSA Laboratories
Obsoletes: 2459                                                  W. Polk
Category: Standards Track                                           NIST
                                                                 W. Ford
                                                                VeriSign
                                                                 D. Solo
                                                               Citigroup
                                                              April 2002

                Internet X.509 Public Key Infrastructure
       Certificate and Certificate Revocation List (CRL) Profile

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This memo profiles the X.509 v3 certificate and X.509 v2 Certificate
   Revocation List (CRL) for use in the Internet.  An overview of this
   approach and model are provided as an introduction.  The X.509 v3
   certificate format is described in detail, with additional
   information regarding the format and semantics of Internet name
   forms.  Standard certificate extensions are described and two
   Internet-specific extensions are defined.  A set of required
   certificate extensions is specified.  The X.509 v2 CRL format is
   described in detail, and required extensions are defined.  An
   algorithm for X.509 certification path validation is described.  An
   ASN.1 module and examples are provided in the appendices.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . .   4
   2  Requirements and Assumptions  . . . . . . . . . . . . . .   5
   2.1  Communication and Topology  . . . . . . . . . . . . . .   6
   2.2  Acceptability Criteria  . . . . . . . . . . . . . . . .   6
   2.3  User Expectations . . . . . . . . . . . . . . . . . . .   7
   2.4  Administrator Expectations  . . . . . . . . . . . . . .   7
   3  Overview of Approach  . . . . . . . . . . . . . . . . . .   7

   3.1  X.509 Version 3 Certificate . . . . . . . . . . . . . .   8
   3.2  Certification Paths and Trust . . . . . . . . . . . . .   9
   3.3  Revocation  . . . . . . . . . . . . . . . . . . . . . .  11
   3.4  Operational Protocols . . . . . . . . . . . . . . . . .  13
   3.5  Management Protocols  . . . . . . . . . . . . . . . . .  13
   4  Certificate and Certificate Extensions Profile  . . . . .  14
   4.1  Basic Certificate Fields  . . . . . . . . . . . . . . .  15
   4.1.1  Certificate Fields  . . . . . . . . . . . . . . . . .  16
   4.1.1.1  tbsCertificate  . . . . . . . . . . . . . . . . . .  16
   4.1.1.2  signatureAlgorithm  . . . . . . . . . . . . . . . .  16
   4.1.1.3  signatureValue  . . . . . . . . . . . . . . . . . .  16
   4.1.2  TBSCertificate  . . . . . . . . . . . . . . . . . . .  17
   4.1.2.1  Version . . . . . . . . . . . . . . . . . . . . . .  17
   4.1.2.2  Serial number . . . . . . . . . . . . . . . . . . .  17
   4.1.2.3  Signature . . . . . . . . . . . . . . . . . . . . .  18
   4.1.2.4  Issuer  . . . . . . . . . . . . . . . . . . . . . .  18
   4.1.2.5  Validity  . . . . . . . . . . . . . . . . . . . . .  22
   4.1.2.5.1  UTCTime . . . . . . . . . . . . . . . . . . . . .  22
   4.1.2.5.2  GeneralizedTime . . . . . . . . . . . . . . . . .  22
   4.1.2.6  Subject . . . . . . . . . . . . . . . . . . . . . .  23
   4.1.2.7  Subject Public Key Info . . . . . . . . . . . . . .  24
   4.1.2.8  Unique Identifiers  . . . . . . . . . . . . . . . .  24
   4.1.2.9 Extensions . . . . . . . . . . . . . . . . . . . . .  24
   4.2  Certificate Extensions  . . . . . . . . . . . . . . . .  24
   4.2.1  Standard Extensions . . . . . . . . . . . . . . . . .  25
   4.2.1.1  Authority Key Identifier  . . . . . . . . . . . . .  26
   4.2.1.2  Subject Key Identifier  . . . . . . . . . . . . . .  27
   4.2.1.3  Key Usage . . . . . . . . . . . . . . . . . . . . .  28
   4.2.1.4  Private Key Usage Period  . . . . . . . . . . . . .  29
   4.2.1.5  Certificate Policies  . . . . . . . . . . . . . . .  30
   4.2.1.6  Policy Mappings . . . . . . . . . . . . . . . . . .  33
   4.2.1.7  Subject Alternative Name  . . . . . . . . . . . . .  33
   4.2.1.8  Issuer Alternative Name . . . . . . . . . . . . . .  36
   4.2.1.9  Subject Directory Attributes  . . . . . . . . . . .  36
   4.2.1.10  Basic Constraints  . . . . . . . . . . . . . . . .  36
   4.2.1.11  Name Constraints . . . . . . . . . . . . . . . . .  37
   4.2.1.12  Policy Constraints . . . . . . . . . . . . . . . .  40
   4.2.1.13  Extended Key Usage . . . . . . . . . . . . . . . .  40
   4.2.1.14  CRL Distribution Points  . . . . . . . . . . . . .  42
   4.2.1.15  Inhibit Any-Policy . . . . . . . . . . . . . . . .  44
   4.2.1.16  Freshest CRL . . . . . . . . . . . . . . . . . . .  44
   4.2.2  Internet Certificate Extensions . . . . . . . . . . .  45
   4.2.2.1  Authority Information Access  . . . . . . . . . . .  45
   4.2.2.2  Subject Information Access  . . . . . . . . . . . .  46
   5  CRL and CRL Extensions Profile  . . . . . . . . . . . . .  48
   5.1  CRL Fields  . . . . . . . . . . . . . . . . . . . . . .  49
   5.1.1  CertificateList Fields  . . . . . . . . . . . . . . .  50
   5.1.1.1  tbsCertList . . . . . . . . . . . . . . . . . . . .  50

   5.1.1.2  signatureAlgorithm  . . . . . . . . . . . . . . . .  50
   5.1.1.3  signatureValue  . . . . . . . . . . . . . . . . . .  51
   5.1.2  Certificate List "To Be Signed" . . . . . . . . . . .  51
   5.1.2.1  Version . . . . . . . . . . . . . . . . . . . . . .  52
   5.1.2.2  Signature . . . . . . . . . . . . . . . . . . . . .  52
   5.1.2.3  Issuer Name . . . . . . . . . . . . . . . . . . . .  52
   5.1.2.4  This Update . . . . . . . . . . . . . . . . . . . .  52
   5.1.2.5  Next Update . . . . . . . . . . . . . . . . . . . .  53
   5.1.2.6  Revoked Certificates  . . . . . . . . . . . . . . .  53
   5.1.2.7  Extensions  . . . . . . . . . . . . . . . . . . . .  53
   5.2  CRL Extensions  . . . . . . . . . . . . . . . . . . . .  53
   5.2.1  Authority Key Identifier  . . . . . . . . . . . . . .  54
   5.2.2  Issuer Alternative Name . . . . . . . . . . . . . . .  54
   5.2.3  CRL Number  . . . . . . . . . . . . . . . . . . . . .  55
   5.2.4  Delta CRL Indicator . . . . . . . . . . . . . . . . .  55
   5.2.5  Issuing Distribution Point  . . . . . . . . . . . . .  58
   5.2.6  Freshest CRL  . . . . . . . . . . . . . . . . . . . .  59
   5.3  CRL Entry Extensions  . . . . . . . . . . . . . . . . .  60
   5.3.1  Reason Code . . . . . . . . . . . . . . . . . . . . .  60
   5.3.2  Hold Instruction Code . . . . . . . . . . . . . . . .  61
   5.3.3  Invalidity Date . . . . . . . . . . . . . . . . . . .  62
   5.3.4  Certificate Issuer  . . . . . . . . . . . . . . . . .  62
   6  Certificate Path Validation . . . . . . . . . . . . . . .  62
   6.1  Basic Path Validation . . . . . . . . . . . . . . . . .  63
   6.1.1  Inputs  . . . . . . . . . . . . . . . . . . . . . . .  66
   6.1.2  Initialization  . . . . . . . . . . . . . . . . . . .  67
   6.1.3  Basic Certificate Processing  . . . . . . . . . . . .  70
   6.1.4  Preparation for Certificate i+1 . . . . . . . . . . .  75
   6.1.5  Wrap-up procedure . . . . . . . . . . . . . . . . . .  78
   6.1.6  Outputs . . . . . . . . . . . . . . . . . . . . . . .  80
   6.2  Extending Path Validation . . . . . . . . . . . . . . .  80
   6.3  CRL Validation  . . . . . . . . . . . . . . . . . . . .  81
   6.3.1  Revocation Inputs . . . . . . . . . . . . . . . . . .  82
   6.3.2  Initialization and Revocation State Variables . . . .  82
   6.3.3  CRL Processing  . . . . . . . . . . . . . . . . . . .  83
   7  References  . . . . . . . . . . . . . . . . . . . . . . .  86
   8  Intellectual Property Rights  . . . . . . . . . . . . . .  88
   9  Security Considerations . . . . . . . . . . . . . . . . .  89
   Appendix A.  ASN.1 Structures and OIDs . . . . . . . . . . .  92
   A.1 Explicitly Tagged Module, 1988 Syntax  . . . . . . . . .  92
   A.2 Implicitly Tagged Module, 1988 Syntax  . . . . . . . . . 105
   Appendix B.  ASN.1 Notes . . . . . . . . . . . . . . . . . . 112
   Appendix C.  Examples  . . . . . . . . . . . . . . . . . . . 115
   C.1  DSA Self-Signed Certificate . . . . . . . . . . . . . . 115
   C.2  End Entity Certificate Using DSA  . . . . . . . . . . . 119
   C.3  End Entity Certificate Using RSA  . . . . . . . . . . . 122
   C.4  Certificate Revocation List . . . . . . . . . . . . . . 126
   Author Addresses . . . . . . . . . . . . . . . . . . . . . . 128

   Full Copyright Statement . . . . . . . . . . . . . . . . . . 129

1  Introduction

   This specification is one part of a family of standards for the X.509
   Public Key Infrastructure (PKI) for the Internet.

   This specification profiles the format and semantics of certificates
   and certificate revocation lists (CRLs) for the Internet PKI.
   Procedures are described for processing of certification paths in the
   Internet environment.  Finally, ASN.1 modules are provided in the
   appendices for all data structures defined or referenced.

   Section 2 describes Internet PKI requirements, and the assumptions
   which affect the scope of this document.  Section 3 presents an
   architectural model and describes its relationship to previous IETF
   and ISO/IEC/ITU-T standards.  In particular, this document's
   relationship with the IETF PEM specifications and the ISO/IEC/ITU-T
   X.509 documents are described.

   Section 4 profiles the X.509 version 3 certificate, and section 5
   profiles the X.509 version 2 CRL.  The profiles include the
   identification of ISO/IEC/ITU-T and ANSI extensions which may be
   useful in the Internet PKI.  The profiles are presented in the 1988
   Abstract Syntax Notation One (ASN.1) rather than the 1997 ASN.1
   syntax used in the most recent ISO/IEC/ITU-T standards.

   Section 6 includes certification path validation procedures.  These
   procedures are based upon the ISO/IEC/ITU-T definition.
   Implementations are REQUIRED to derive the same results but are not
   required to use the specified procedures.

   Procedures for identification and encoding of public key materials
   and digital signatures are defined in [PKIXALGS].  Implementations of
   this specification are not required to use any particular
   cryptographic algorithms.  However, conforming implementations which
   use the algorithms identified in [PKIXALGS] MUST identify and encode
   the public key materials and digital signatures as described in that
   specification.

   Finally, three appendices are provided to aid implementers.  Appendix
   A contains all ASN.1 structures defined or referenced within this
   specification.  As above, the material is presented in the 1988
   ASN.1.  Appendix B contains notes on less familiar features of the
   ASN.1 notation used within this specification.  Appendix C contains
   examples of a conforming certificate and a conforming CRL.

   This specification obsoletes RFC 2459.  This specification differs
   from RFC 2459 in five basic areas:

      * To promote interoperable implementations, a detailed algorithm
      for certification path validation is included in section 6.1 of
      this specification; RFC 2459 provided only a high-level
      description of path validation.

      * An algorithm for determining the status of a certificate using
      CRLs is provided in section 6.3 of this specification.  This
      material was not present in RFC 2459.

      * To accommodate new usage models, detailed information describing
      the use of delta CRLs is provided in Section 5 of this
      specification.

      * Identification and encoding of public key materials and digital
      signatures are not included in this specification, but are now
      described in a companion specification [PKIXALGS].

      * Four additional extensions are specified: three certificate
      extensions and one CRL extension.  The certificate extensions are
      subject info access, inhibit any-policy, and freshest CRL.  The
      freshest CRL extension is also defined as a CRL extension.

      * Throughout the specification, clarifications have been
      introduced to enhance consistency with the ITU-T X.509
      specification.  X.509 defines the certificate and CRL format as
      well as many of the extensions that appear in this specification.
      These changes were introduced to improve the likelihood of
      interoperability between implementations based on this
      specification with implementations based on the ITU-T
      specification.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

2  Requirements and Assumptions

   The goal of this specification is to develop a profile to facilitate
   the 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.  In order to relieve some of the obstacles to using X.509

   certificates, this document defines a profile to promote the
   development of certificate management systems; development of
   application tools; and interoperability determined by policy.

   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).

   A certificate user should review the certificate policy generated by
   the certification authority (CA) before relying on the authentication
   or non-repudiation services associated with the public key in a
   particular certificate.  To this end, this standard does not
   prescribe legally binding rules or duties.

   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 provide more appropriate methods 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
   availability.  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 or a LDAP directory system.  The profile does not prohibit the
   use of an X.500 Directory or a LDAP directory; however, any means of
   distributing certificates and certificate revocation lists (CRLs) may
   be used.

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.
   This profile recognizes the limitations of the platforms these users
   employ and the limitations in sophistication and attentiveness of the
   users themselves.  This manifests itself in minimal user
   configuration responsibility (e.g., trusted CA 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 user expectations, the Internet PKI profile is structured to
   support the individuals who generally operate CAs.  Providing
   administrators with unbounded choices increases the chances that a
   subtle CA administrator mistake will result in broad compromise.
   Also, unbounded choices greatly complicate the software that 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.

   The components in this model are:

   end entity: user of PKI certificates and/or end user system that is
               the subject of a certificate;
   CA:         certification authority;
   RA:         registration authority, i.e., an optional system to which
               a CA delegates certain management functions;
   CRL issuer: an optional system to which a CA delegates the
               publication of certificate revocation lists;
   repository: a system or collection of distributed systems that stores
               certificates and CRLs and serves as a means of
               distributing these certificates and CRLs to end entities.

   Note that an Attribute Authority (AA) might also choose to delegate
   the publication of CRLs to a CRL issuer.

   +---+
   | C |                       +------------+
   | e | <-------------------->| End entity |
   | r |       Operational     +------------+
   | t |       transactions          ^
   | i |      and management         |  Management
   | f |       transactions          |  transactions        PKI
   | i |                             |                     users
   | c |                             v
   | a | =======================  +--+------------+  ==============
   | t |                          ^               ^
   | e |                          |               |         PKI
   |   |                          v               |      management
   | & |                       +------+           |       entities
   |   | <---------------------|  RA  |<----+     |
   | C |  Publish certificate  +------+     |     |
   | R |                                    |     |
   | L |                                    |     |
   |   |                                    v     v
   | R |                                +------------+
   | e | <------------------------------|     CA     |
   | p |   Publish certificate          +------------+
   | o |   Publish CRL                     ^      ^
   | s |                                   |      |  Management
   | i |                +------------+     |      |  transactions
   | t | <--------------| CRL Issuer |<----+      |
   | o |   Publish CRL  +------------+            v
   | r |                                      +------+
   | y |                                      |  CA  |
   +---+                                      +------+

                      Figure 1 - PKI Entities

3.1  X.509 Version 3 Certificate

   Users of a public key require confidence that the associated private
   key is owned by 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 subjects.  The binding is asserted by having a trusted CA
   digitally sign each certificate.  The CA may base this assertion upon
   technical means (a.k.a., proof of possession through a challenge-
   response protocol), presentation of the private key, or on an
   assertion by the subject.  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.

   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 [X.509].  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.

   The Internet Privacy Enhanced Mail (PEM) RFCs, 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 had proven necessary.  In response to these new
   requirements, ISO/IEC, ITU-T 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].

   ISO/IEC, ITU-T, and ANSI X9 have also developed standard extensions
   for use in the v3 extensions field [X.509][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, ITU-T, and ANSI X9 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
   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,
   the CA's name, and related information (such as the validity period
   or name constraints), 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 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
      shall 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 digital 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
   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 uses the X.509 v1 certificate formats.  The limitations
   of X.509 v1 required imposition of several structural restrictions to
   clearly associate policy information or restrict the utility of
   certificates.  These restrictions included:

      (a)  a pure top-down hierarchy, with all certification paths
      starting from IPRA;

      (b)  a naming subordination rule restricting the names of a CA's
      subjects; and

      (c)  use of the PCA concept, which requires knowledge of
      individual PCAs to be built into certificate chain verification
      logic.  Knowledge of individual PCAs was required to determine if
      a chain could be accepted.

   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.  As a result, this document supports a more flexible
   architecture, including:

      (a)  Certification paths start with a public key of a CA in a
      user's own domain, or with the public key of the top of a
      hierarchy.  Starting with the public key of a CA in a user's own
      domain has certain advantages.  In some environments, the local
      domain is the most trusted.

      (b)  Name constraints may be imposed through explicit inclusion of
      a name constraints extension in a certificate, but are not
      required.

      (c)  Policy extensions and policy mappings replace the PCA
      concept, which permits a greater degree of automation.  The
      application can determine if the certification path is acceptable
      based on the contents of the certificates instead of a priori
      knowledge of PCAs.  This permits automation of certification path
      processing.

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 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 or CRL
   issuer 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
   new CRL is issued on a regular periodic basis (e.g., hourly, daily,
   or weekly).  An entry is added to the CRL as part of the next update
   following notification of revocation.  An entry MUST NOT be removed
   from the CRL until it appears on one regularly scheduled CRL issued
   beyond the revoked certificate's validity period.

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

   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 all currently issued CRLs
   are updated -- this may be up to one hour, one day, or one week
   depending on the frequency that CRLs are issued.

   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 that profile.  However, this profile does not
   require the issuance of CRLs.  Message formats and protocols
   supporting on-line revocation notification are defined in other PKIX
   specifications.  On-line methods of revocation notification may be
   applicable in some environments as an alternative to the X.509 CRL.
   On-line revocation checking may significantly reduce the latency
   between a revocation report and the distribution of the information
   to relying parties.  Once the CA accepts a revocation report as
   authentic and valid, any query to the on-line service will correctly
   reflect the certificate validation impacts of the revocation.
   However, these methods impose new security requirements: the
   certificate validator needs to trust the on-line validation service
   while the repository does not need to be trusted.

3.4  Operational Protocols

   Operational protocols are required to deliver certificates and CRLs
   (or status information) to certificate using client systems.
   Provisions are needed for a variety of different means of certificate
   and CRL delivery, including distribution procedures based on LDAP,
   HTTP, FTP, and X.500.  Operational protocols supporting these
   functions are defined in other PKIX specifications.  These
   specifications may include definitions of 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 PKI user and management entities.  For example, a 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 (directly, or through an RA), prior to that
      CA issuing  a certificate or certificates for that user.

      (b)  initialization:  Before a client system can operate securely
      it is necessary to install 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 and other assured information of
      the trusted CA(s), 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
      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.  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 information used in
      establishing a cross-certificate.  A cross-certificate is a
      certificate issued by one CA to another CA which contains a CA
      signature key used for issuing certificates.

   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 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.

   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 (e.g., e-mail, file
   transfer, and WWW) are described in those specifications.

4  Certificate and Certificate Extensions Profile

   This section presents a profile for public key certificates that will
   foster interoperability and a reusable PKI.  This section is based
   upon the X.509 v3 certificate format and the standard certificate
   extensions defined in [X.509].  The ISO/IEC and ITU-T documents use
   the 1997 version of ASN.1; while this document uses the 1988 ASN.1
   syntax, the encoded certificate and standard extensions are
   equivalent.  This section also defines private extensions required to
   support a PKI 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.

4.1  Basic Certificate Fields

   The X.509 v3 certificate basic syntax is as follows.  For signature
   calculation, the data that is to be signed is encoded using the ASN.1
   distinguished encoding rules (DER) [X.690].  ASN.1 DER encoding is a
   tag, length, value encoding system for each element.

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

   TBSCertificate  ::=  SEQUENCE  {
        version         [0]  EXPLICIT 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]  EXPLICIT Extensions OPTIONAL
                             -- If present, version MUST be v3
        }

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

   CertificateSerialNumber  ::=  INTEGER

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

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

   UniqueIdentifier  ::=  BIT STRING

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

   Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

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

   The following items describe the X.509 v3 certificate for use in the
   Internet.

4.1.1  Certificate Fields

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

4.1.1.1  tbsCertificate

   The field contains the names of the subject and issuer, a public key
   associated with the subject, a validity period, and other associated
   information.  The fields are described in detail in section 4.1.2;
   the tbsCertificate usually includes extensions which are described in
   section 4.2.

4.1.1.2  signatureAlgorithm

   The signatureAlgorithm field contains the identifier for the
   cryptographic algorithm used by the CA to sign this certificate.
   [PKIXALGS] lists supported signature algorithms, but other signature
   algorithms MAY also be supported.

   An algorithm identifier is defined by the following ASN.1 structure:

   AlgorithmIdentifier  ::=  SEQUENCE  {
        algorithm               OBJECT IDENTIFIER,
        parameters              ANY DEFINED BY algorithm OPTIONAL  }

   The algorithm identifier is used to identify a cryptographic
   algorithm.  The OBJECT IDENTIFIER component identifies the algorithm
   (such as DSA with SHA-1).  The contents of the optional parameters
   field will vary according to the algorithm identified.

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

4.1.1.3  signatureValue

   The signatureValue 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 the signature function.  This

   signature value is encoded as a BIT STRING and included in the
   signature field.  The details of this process are specified for each
   of algorithms listed in [PKIXALGS].

   By generating this signature, a CA certifies the validity of the
   information in the tbsCertificate field.  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 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, a validity period, a version number,
   and a serial number; some MAY contain optional unique identifier
   fields.  The remainder of this section describes the syntax and
   semantics of these fields.  A TBSCertificate usually includes
   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, version MUST be 3
   (value is 2).  If no extensions are present, but a UniqueIdentifier
   is present, the version SHOULD be 2 (value is 1); however version MAY
   be 3.  If only basic fields are present, the version SHOULD be 1 (the
   value is omitted from the certificate as the default value); however
   the version MAY be 2 or 3.

   Implementations SHOULD be prepared to accept any version certificate.
   At a minimum, conforming implementations MUST recognize version 3
   certificates.

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

4.1.2.2  Serial number

   The serial number MUST be a positive integer assigned by the CA 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).  CAs MUST force the serialNumber to be a non-negative
   integer.

   Given the uniqueness requirements above, serial numbers can be
   expected to contain long integers.  Certificate users MUST be able to
   handle serialNumber values up to 20 octets.  Conformant CAs MUST NOT
   use serialNumber values longer than 20 octets.

   Note: Non-conforming CAs may issue certificates with serial numbers
   that are negative, or zero.  Certificate users SHOULD be prepared to
   gracefully handle such certificates.

4.1.2.3  Signature

   This field contains the algorithm identifier for the algorithm used
   by the CA to sign the certificate.

   This field MUST contain the same algorithm identifier as the
   signatureAlgorithm field in the sequence Certificate (section
   4.1.1.2).  The contents of the optional parameters field will vary
   according to the algorithm identified.  [PKIXALGS] lists the
   supported signature algorithms, but other signature algorithms MAY
   also be supported.

4.1.2.4  Issuer

   The issuer field identifies the entity who has signed and issued the
   certificate.  The issuer field MUST contain a non-empty distinguished
   name (DN).  The issuer field is defined as the X.501 type Name
   [X.501].  Name is defined by the following ASN.1 structures:

   Name ::= CHOICE {
     RDNSequence }

   RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

   RelativeDistinguishedName ::=
     SET OF AttributeTypeAndValue

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

   AttributeType ::= OBJECT IDENTIFIER

   AttributeValue ::= ANY DEFINED BY AttributeType

   DirectoryString ::= CHOICE {
         teletexString           TeletexString (SIZE (1..MAX)),
         printableString         PrintableString (SIZE (1..MAX)),
         universalString         UniversalString (SIZE (1..MAX)),
         utf8String              UTF8String (SIZE (1..MAX)),
         bmpString               BMPString (SIZE (1..MAX)) }

   The Name describes a hierarchical name composed of attributes, such
   as country name, and corresponding values, such as US.  The type of
   the component AttributeValue is determined by the AttributeType; in
   general it will be a DirectoryString.

   The DirectoryString type is defined as a choice of PrintableString,
   TeletexString, BMPString, UTF8String, and UniversalString.  The
   UTF8String encoding [RFC 2279] is the preferred encoding, and all
   certificates issued after December 31, 2003 MUST use the UTF8String
   encoding of DirectoryString (except as noted below).  Until that
   date, conforming CAs MUST choose from the following options when
   creating a distinguished name, including their own:

      (a)  if the character set is sufficient, the string MAY be
      represented as a PrintableString;

      (b)  failing (a), if the BMPString character set is sufficient the
      string MAY be represented as a BMPString; and

      (c)  failing (a) and (b), the string MUST be represented as a
      UTF8String.  If (a) or (b) is satisfied, the CA MAY still choose
      to represent the string as a UTF8String.

   Exceptions to the December 31, 2003 UTF8 encoding requirements are as
   follows:

      (a)  CAs MAY issue "name rollover" certificates to support an
      orderly migration to UTF8String encoding.  Such certificates would
      include the CA's UTF8String encoded name as issuer and and the old
      name encoding as subject, or vice-versa.

      (b)  As stated in section 4.1.2.6, the subject field MUST be
      populated with a non-empty distinguished name matching the
      contents of the issuer field in all certificates issued by the
      subject CA regardless of encoding.

   The TeletexString and UniversalString are included for backward
   compatibility, and SHOULD NOT be used for certificates for new
   subjects.  However, these types MAY be used in certificates where the
   name was previously established.  Certificate users SHOULD be
   prepared to receive certificates with these types.

   In addition, many legacy implementations support names encoded in the
   ISO 8859-1 character set (Latin1String) [ISO 8859-1] but tag them as
   TeletexString.  TeletexString encodes a larger character set than ISO
   8859-1, but it encodes some characters differently.  Implementations
   SHOULD be prepared to handle both encodings.

   As noted above, distinguished names are composed of attributes.  This
   specification does not restrict the set of attribute types that may
   appear in names.  However, conforming implementations MUST be
   prepared to receive certificates with issuer names containing the set
   of attribute types defined below.  This specification RECOMMENDS
   support for additional attribute types.

   Standard sets of attributes have been defined in the X.500 series of
   specifications [X.520].  Implementations of this specification MUST
   be prepared to receive the following standard attribute types in
   issuer and subject (section 4.1.2.6) names:

      * country,
      * organization,
      * organizational-unit,
      * distinguished name qualifier,
      * state or province name,
      * common name (e.g., "Susan Housley"), and
      * serial number.

   In addition, implementations of this specification SHOULD be prepared
   to receive the following standard attribute types in issuer and
   subject names:

      * locality,
      * title,
      * surname,
      * given name,
      * initials,
      * pseudonym, and
      * generation qualifier (e.g., "Jr.", "3rd", or "IV").

   The syntax and associated object identifiers (OIDs) for these
   attribute types are provided in the ASN.1 modules in Appendix A.

   In addition, implementations of this specification MUST be prepared
   to receive the domainComponent attribute, as defined in [RFC 2247].
   The Domain Name System (DNS) provides a hierarchical resource
   labeling system.  This attribute provides a convenient mechanism for
   organizations that wish to use DNs that parallel their DNS names.
   This is not a replacement for the dNSName component of the

   alternative name field.  Implementations are not required to convert
   such names into DNS names.  The syntax and associated OID for this
   attribute type is provided in the ASN.1 modules in Appendix A.

   Certificate users MUST be prepared to process the issuer
   distinguished name and subject distinguished name (section 4.1.2.6)
   fields to perform name chaining for certification path validation
   (section 6).  Name chaining is performed by matching the issuer
   distinguished name in one certificate with the subject name in a CA
   certificate.

   This specification requires only a subset of the name comparison
   functionality specified in the X.500 series of specifications.
   Conforming implementations are REQUIRED to implement the following
   name comparison rules:

      (a)  attribute values encoded in different types (e.g.,
      PrintableString and BMPString) MAY be assumed to represent
      different strings;

      (b) attribute values in types other than PrintableString are case
      sensitive (this permits matching of attribute values as binary
      objects);

      (c)  attribute values in PrintableString are not case sensitive
      (e.g., "Marianne Swanson" is the same as "MARIANNE SWANSON"); and

      (d)  attribute values in PrintableString are compared after
      removing leading and trailing white space and converting internal
      substrings of one or more consecutive white space characters to a
      single space.

   These name comparison rules permit a certificate user to validate
   certificates issued using languages or encodings unfamiliar to the
   certificate user.

   In addition, implementations of this specification MAY use these
   comparison rules to process unfamiliar attribute types for name
   chaining.  This allows implementations to process certificates with
   unfamiliar attributes in the issuer name.

   Note that the comparison rules defined in the X.500 series of
   specifications indicate that the character sets used to encode data
   in distinguished names are irrelevant.  The characters themselves are
   compared without regard to encoding.  Implementations of this profile
   are permitted to use the comparison algorithm defined in the X.500
   series.  Such an implementation will recognize a superset of name
   matches recognized by the algorithm specified above.

4.1.2.5  Validity

   The certificate validity period is the time interval during which the
   CA warrants that it will maintain information about the status of the
   certificate.  The field is represented as a SEQUENCE of two dates:
   the date on which the certificate validity period begins (notBefore)
   and the date on which the certificate validity period ends
   (notAfter).  Both notBefore and notAfter may be encoded as UTCTime or
   GeneralizedTime.

   CAs conforming to this profile MUST always encode certificate
   validity dates through the year 2049 as UTCTime; certificate validity
   dates in 2050 or later MUST be encoded as GeneralizedTime.

   The validity period for a certificate is the period of time from
   notBefore through notAfter, inclusive.

4.1.2.5.1  UTCTime

   The universal time type, UTCTime, is a standard ASN.1 type intended
   for representation of dates and time.  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 MUST be expressed
   Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are
   YYMMDDHHMMSSZ), even where the number of seconds is zero.  Conforming
   systems MUST interpret the year field (YY) as follows:

      Where YY is greater than or equal to 50, the year SHALL be
      interpreted as 19YY; and

      Where YY is less than 50, the year SHALL be interpreted as 20YY.

4.1.2.5.2  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 MUST be
   expressed Greenwich Mean Time (Zulu) and MUST include seconds (i.e.,
   times are YYYYMMDDHHMMSSZ), even where the number of seconds is zero.
   GeneralizedTime values MUST NOT include fractional seconds.

4.1.2.6  Subject

   The subject field identifies the entity associated with the public
   key stored in the subject public key field.  The subject name MAY be
   carried in the subject field and/or the subjectAltName extension.  If
   the subject is a CA (e.g., the basic constraints extension, as
   discussed in 4.2.1.10, is present and the value of cA is TRUE), then
   the subject field MUST be populated with a non-empty distinguished
   name matching the contents of the issuer field (section 4.1.2.4) in
   all certificates issued by the subject CA.  If the subject is a CRL
   issuer (e.g., the key usage extension, as discussed in 4.2.1.3, is
   present and the value of cRLSign is TRUE) then the subject field MUST
   be populated with a non-empty distinguished name matching the
   contents of the issuer field (section 4.1.2.4) in all CRLs issued by
   the subject CRL issuer.  If subject naming information is present
   only in the subjectAltName extension (e.g., a key bound only to an
   email address or URI), then the subject name MUST be an empty
   sequence and the subjectAltName extension MUST be critical.

   Where it is non-empty, the subject field MUST contain an X.500
   distinguished name (DN).  The DN MUST be unique for each subject
   entity certified by the one CA as defined by the issuer name field.
   A CA MAY issue more than one certificate with the same DN to the same
   subject entity.

   The subject name field is defined as the X.501 type Name.
   Implementation requirements for this field are those defined for the
   issuer field (section 4.1.2.4).  When encoding attribute values of
   type DirectoryString, the encoding rules for the issuer field MUST be
   implemented.  Implementations of this specification MUST be prepared
   to receive subject names containing the attribute types required for
   the issuer field.  Implementations of this specification SHOULD be
   prepared to receive subject names containing the recommended
   attribute types for the issuer field.  The syntax and associated
   object identifiers (OIDs) for these attribute types are provided in
   the ASN.1 modules in Appendix A.  Implementations of this
   specification MAY use these comparison rules to process unfamiliar
   attribute types (i.e., for name chaining).  This allows
   implementations to process certificates with unfamiliar attributes in
   the subject name.

   In addition, legacy implementations exist where an RFC 822 name is
   embedded in the subject distinguished name as an EmailAddress
   attribute.  The attribute value for EmailAddress is of type IA5String
   to permit inclusion of the character '@', which is not part of the
   PrintableString character set.  EmailAddress attribute values are not
   case sensitive (e.g., "fanfeedback@redsox.com" is the same as
   "FANFEEDBACK@REDSOX.COM").

   Conforming implementations generating new certificates with
   electronic mail addresses MUST use the rfc822Name in the subject
   alternative name field (section 4.2.1.7) to describe such identities.
   Simultaneous inclusion of the EmailAddress attribute in the subject
   distinguished name to support legacy implementations is deprecated
   but permitted.

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 (e.g., RSA, DSA, or Diffie-Hellman).  The
   algorithm is identified using the AlgorithmIdentifier structure
   specified in section 4.1.1.2.  The object identifiers for the
   supported algorithms and the methods for encoding the public key
   materials (public key and parameters) are specified in [PKIXALGS].

4.1.2.8  Unique Identifiers

   These fields MUST only appear if the version is 2 or 3 (section
   4.1.2.1).  These fields MUST NOT appear if the version is 1.  The
   subject and issuer unique identifiers 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 for
   different entities 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.

4.1.2.9  Extensions

   This field MUST only appear if the version is 3 (section 4.1.2.1).
   If present, this field is a SEQUENCE of one or more certificate
   extensions.  The format and content of certificate extensions in the
   Internet PKI is defined in section 4.2.

4.2  Certificate Extensions

   The extensions defined for X.509 v3 certificates provide methods for
   associating additional attributes with users or public keys and for
   managing a certification hierarchy.  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 is designated as either critical or non-critical.  A
   certificate using system MUST reject the certificate if it encounters
   a critical extension it does not recognize; however, a non-critical
   extension MAY be ignored if it is not recognized.  The following
   sections present recommended extensions used within Internet

   certificates and standard locations for information.  Communities may
   elect to use additional extensions; however, caution ought to be
   exercised in adopting any critical extensions in certificates which
   might prevent use in a general context.

   Each extension includes an OID and an ASN.1 structure.  When an
   extension appears in a certificate, the OID appears as the field
   extnID and the corresponding ASN.1 encoded structure is the value of
   the octet string extnValue.  A certificate MUST NOT include more than
   one instance of a particular extension.  For example, a certificate
   may contain only one authority key identifier extension (section
   4.2.1.1).  An extension includes the boolean critical, with a default
   value of FALSE.  The text for each extension specifies the acceptable
   values for the critical field.

   Conforming CAs MUST support key identifiers (sections 4.2.1.1 and
   4.2.1.2), basic constraints (section 4.2.1.10), key usage (section
   4.2.1.3), and certificate policies (section 4.2.1.5) extensions.  If
   the CA issues certificates with an empty sequence for the subject
   field, the CA MUST support the subject alternative name extension
   (section 4.2.1.7).  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 MUST recognize
   the following extensions: key usage (section 4.2.1.3), certificate
   policies (section 4.2.1.5), the subject alternative name (section
   4.2.1.7), basic constraints (section 4.2.1.10), name constraints
   (section 4.2.1.11), policy constraints (section 4.2.1.12), extended
   key usage (section 4.2.1.13), and inhibit any-policy (section
   4.2.1.15).

   In addition, applications conforming to this profile SHOULD recognize
   the authority and subject key identifier (sections 4.2.1.1 and
   4.2.1.2), and policy mapping (section 4.2.1.6) extensions.

4.2.1  Standard Extensions

   This section identifies standard certificate extensions defined in
   [X.509] for use in the Internet PKI.  Each extension is associated
   with an OID defined in [X.509].  These OIDs are members of the id-ce
   arc, which is defined by the following:

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

4.2.1.1  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the public key corresponding to the private key used to
   sign a certificate.  This extension is used where an issuer has
   multiple signing keys (either due to multiple concurrent key pairs or
   due to changeover).  The identification MAY 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 keyIdentifier field of the authorityKeyIdentifier extension MUST
   be included in all certificates generated by conforming CAs to
   facilitate certification path construction.  There is one exception;
   where a CA distributes its public key in the form of a "self-signed"
   certificate, the authority key identifier MAY be omitted.  The
   signature on a self-signed certificate is generated with the private
   key associated with the certificate's subject public key.  (This
   proves that the issuer possesses both the public and private keys.)
   In this case, the subject and authority key identifiers would be
   identical, but only the subject key identifier is needed for
   certification path building.

   The value of the keyIdentifier field SHOULD be derived from the
   public key used to verify the certificate's signature or a method
   that generates unique values.  Two common methods for generating key
   identifiers from the public key, and one common method for generating
   unique values, are described in section 4.2.1.2.  Where a key
   identifier has not been previously established, this specification
   RECOMMENDS use of one of these methods for generating keyIdentifiers.
   Where a key identifier has been previously established, the CA SHOULD
   use the previously established identifier.

   This profile RECOMMENDS support for the key identifier method by all
   certificate users.

   This extension MUST 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
   certificates that contain a particular public key.

   To facilitate certification path construction, this extension MUST
   appear in all conforming CA certificates, that is, all certificates
   including the basic constraints extension (section 4.2.1.10) where
   the value of cA is TRUE.  The value of the subject key identifier
   MUST be the value placed in the key identifier field of the Authority
   Key Identifier extension (section 4.2.1.1) of certificates issued by
   the subject of this certificate.

   For CA certificates, subject key identifiers SHOULD be derived from
   the public key or a method that generates unique values.  Two common
   methods for generating key identifiers from the public key are:

      (1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the
      value of the BIT STRING subjectPublicKey (excluding the tag,
      length, and number of unused bits).

      (2) The keyIdentifier is composed of a four bit type field with
      the value 0100 followed by the least significant 60 bits of the
      SHA-1 hash of the value of the BIT STRING subjectPublicKey
      (excluding the tag, length, and number of unused bit string bits).

   One common method for generating unique values is a monotonically
   increasing sequence of integers.

   For end entity certificates, the subject key identifier extension
   provides a means for identifying certificates containing the
   particular public key used in an application.  Where an end entity
   has obtained multiple certificates, especially from multiple CAs, the
   subject key identifier provides a means to quickly identify the set
   of certificates containing a particular public key.  To assist
   applications in identifying the appropriate end entity certificate,
   this extension SHOULD be included in all end entity certificates.

   For end entity certificates, subject key identifiers SHOULD be
   derived from the public key.  Two common methods for generating key
   identifiers from the public key are identified above.

   Where a key identifier has not been previously established, this
   specification RECOMMENDS use of one of these methods for generating
   keyIdentifiers.  Where a key identifier has been previously
   established, the CA SHOULD use the previously established identifier.

   This extension MUST NOT be marked 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 key that
   could be used for more than one operation is to be restricted.  For
   example, when an RSA key should be used only to verify signatures on
   objects other than public key certificates and CRLs, the
   digitalSignature and/or nonRepudiation bits would be asserted.
   Likewise, when an RSA key should be used only for key management, the
   keyEncipherment bit would be asserted.

   This extension MUST appear in certificates that contain public keys
   that are used to validate digital signatures on other public key
   certificates or CRLs.  When this extension appears, it SHOULD be
   marked critical.

      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),
           encipherOnly            (7),
           decipherOnly            (8) }

   Bits in the KeyUsage type are used as follows:

      The digitalSignature bit is asserted when the subject public key
      is used with a digital signature mechanism to support security
      services other than certificate signing (bit 5), or CRL signing
      (bit 6).  Digital signature mechanisms are often used for entity
      authentication and data origin authentication with integrity.

      The nonRepudiation bit is asserted when the subject public key is
      used to verify digital signatures used to provide a non-
      repudiation service which protects against the signing entity
      falsely denying some action, excluding certificate or CRL signing.
      In the case of later conflict, a reliable third party may
      determine the authenticity of the signed data.

      Further distinctions between the digitalSignature and
      nonRepudiation bits may be provided in specific certificate
      policies.

      The keyEncipherment bit is asserted when the subject public key is
      used for key transport.  For example, when an RSA key is to be
      used for key management, then this bit is set.

      The dataEncipherment bit is asserted when the subject public key
      is used for enciphering user data, other than cryptographic keys.

      The keyAgreement bit is asserted when the subject public key is
      used for key agreement.  For example, when a Diffie-Hellman key is
      to be used for key management, then this bit is set.

      The keyCertSign bit is asserted when the subject public key is
      used for verifying a signature on public key certificates.  If the
      keyCertSign bit is asserted, then the cA bit in the basic
      constraints extension (section 4.2.1.10) MUST also be asserted.

      The cRLSign bit is asserted when the subject public key is used
      for verifying a signature on certificate revocation list (e.g., a
      CRL, delta CRL, or an ARL).  This bit MUST be asserted in
      certificates that are used to verify signatures on CRLs.

      The meaning of the encipherOnly bit is undefined in the absence of
      the keyAgreement bit.  When the encipherOnly bit is asserted and
      the keyAgreement bit is also set, the subject public key may be
      used only for enciphering data while performing key agreement.

      The meaning of the decipherOnly bit is undefined in the absence of
      the keyAgreement bit.  When the decipherOnly bit is asserted and
      the keyAgreement bit is also set, the subject public key may be
      used only for deciphering data while performing key agreement.

   This profile does not restrict the combinations of bits that may be
   set in an instantiation of the keyUsage extension.  However,
   appropriate values for keyUsage extensions for particular algorithms
   are specified in [PKIXALGS].

4.2.1.4  Private Key Usage Period

   This extension SHOULD NOT be used within the Internet PKI.  CAs
   conforming to this profile MUST NOT generate certificates that
   include a critical private key usage period extension.

   The private key usage period extension allows the certificate issuer
   to specify a different validity 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 MUST NOT generate certificates with private key usage
   period extensions unless at least one of the two components is
   present and the extension is non-critical.

   Where used, notBefore and notAfter are represented as GeneralizedTime
   and MUST be specified and interpreted as defined in section
   4.1.2.5.2.

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

   PrivateKeyUsagePeriod ::= SEQUENCE {
        notBefore       [0]     GeneralizedTime OPTIONAL,
        notAfter        [1]     GeneralizedTime OPTIONAL }

4.2.1.5  Certificate Policies

   The certificate policies extension contains a sequence of one or more
   policy information terms, each of which consists of an object
   identifier (OID) and optional qualifiers.  Optional qualifiers, which
   MAY be present, are not expected to change the definition of the
   policy.

   In an end entity certificate, these policy information terms indicate
   the policy under which the certificate has been issued and the
   purposes for which the certificate may be used.  In a CA certificate,
   these policy information terms limit the set of policies for
   certification paths which include this certificate.  When a CA does
   not wish to limit the set of policies for certification paths which
   include this certificate, it MAY assert the special policy anyPolicy,
   with a value of { 2 5 29 32 0 }.

   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 (including the optional qualifier), or MUST reject the
   certificate.

   To promote interoperability, this profile RECOMMENDS that policy
   information terms consist of only an OID.  Where an OID alone is
   insufficient, this profile strongly recommends that use of qualifiers

   be limited to those identified in this section.  When qualifiers are
   used with the special policy anyPolicy, they MUST be limited to the
   qualifiers identified in this section.

   This specification defines two policy qualifier types for use by
   certificate policy writers and certificate issuers.  The qualifier
   types are the CPS Pointer and User Notice qualifiers.

   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.  Processing requirements for this qualifier are a
   local matter.  No action is mandated by this specification regardless
   of the criticality value asserted for the extension.

   User notice is intended for display to a relying party when a
   certificate is used.  The application software SHOULD display all
   user notices in all certificates of the certification path used,
   except that if a notice is duplicated only one copy need be
   displayed.  To prevent such duplication, this qualifier SHOULD only
   be present in end entity certificates and CA certificates issued to
   other organizations.

   The user notice has two optional fields: the noticeRef field and the
   explicitText field.

      The noticeRef field, if used, names an organization and
      identifies, by number, a particular textual statement prepared by
      that organization.  For example, it might identify the
      organization "CertsRUs" and notice number 1.  In a typical
      implementation, the application software will have a notice file
      containing the current set of notices for CertsRUs; the
      application will extract the notice text from the file and display
      it.  Messages MAY be multilingual, allowing the software to select
      the particular language message for its own environment.

      An explicitText field includes the textual statement directly in
      the certificate.  The explicitText field is a string with a
      maximum size of 200 characters.

   If both the noticeRef and explicitText options are included in the
   one qualifier and if the application software can locate the notice
   text indicated by the noticeRef option, then that text SHOULD be
   displayed; otherwise, the explicitText string SHOULD be displayed.

   Note: While the explicitText has a maximum size of 200 characters,
   some non-conforming CAs exceed this limit.  Therefore, certificate
   users SHOULD gracefully handle explicitText with more than 200
   characters.

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

   anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificate-policies 0 }

   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  PolicyQualifierId,
        qualifier          ANY DEFINED BY policyQualifierId }

   -- policyQualifierIds for Internet policy qualifiers

   id-qt          OBJECT IDENTIFIER ::=  { id-pkix 2 }
   id-qt-cps      OBJECT IDENTIFIER ::=  { id-qt 1 }
   id-qt-unotice  OBJECT IDENTIFIER ::=  { id-qt 2 }

   PolicyQualifierId ::=
        OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

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

   CPSuri ::= IA5String

   UserNotice ::= SEQUENCE {
        noticeRef        NoticeReference OPTIONAL,
        explicitText     DisplayText OPTIONAL}

   NoticeReference ::= SEQUENCE {
        organization     DisplayText,
        noticeNumbers    SEQUENCE OF INTEGER }

   DisplayText ::= CHOICE {
        ia5String        IA5String      (SIZE (1..200)),
        visibleString    VisibleString  (SIZE (1..200)),
        bmpString        BMPString      (SIZE (1..200)),
        utf8String       UTF8String     (SIZE (1..200)) }

4.2.1.6  Policy Mappings

   This extension is used in CA certificates.  It lists one or more
   pairs of OIDs; 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 might accept an issuerDomainPolicy for certain
   applications.  The policy mapping defines the list of policies
   associated with the subject CA that may be accepted as comparable to
   the issuerDomainPolicy.

   Each issuerDomainPolicy named in the policy mapping extension SHOULD
   also be asserted in a certificate policies extension in the same
   certificate.  Policies SHOULD NOT be mapped either to or from the
   special value anyPolicy (section 4.2.1.5).

   This extension MAY be supported by CAs and/or applications, and it
   MUST be non-critical.

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

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

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 Internet electronic mail address, a DNS name, an IP
   address, and a uniform resource identifier (URI).  Other options
   exist, including completely local definitions.  Multiple name forms,
   and multiple instances of each name form, MAY be included.  Whenever
   such identities are to be bound into a certificate, the subject
   alternative name (or issuer alternative name) extension MUST be used;
   however, a DNS name MAY be represented in the subject field using the
   domainComponent attribute as described in section 4.1.2.4.

   Because the subject alternative name is considered to be definitively
   bound to the public key, all parts of the subject alternative name
   MUST be verified by the CA.

   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 MUST be empty (an empty sequence), and the

   subjectAltName extension MUST be present.  If the subject field
   contains an empty sequence, the subjectAltName extension MUST be
   marked critical.

   When the subjectAltName extension contains an Internet mail address,
   the address MUST be included as an rfc822Name.  The format of an
   rfc822Name is an "addr-spec" as defined in RFC 822 [RFC 822].  An
   addr-spec has the form "local-part@domain".  Note that an addr-spec
   has no phrase (such as a common name) before it, has no comment (text
   surrounded in parentheses) after it, and is not surrounded by "<" and
   ">".  Note that while upper and lower case letters are allowed in an
   RFC 822 addr-spec, no significance is attached to the case.

   When the subjectAltName extension contains a iPAddress, the address
   MUST be stored in the octet string in "network byte order," as
   specified in RFC 791 [RFC 791].  The least significant bit (LSB) of
   each octet is the LSB of the corresponding byte in the network
   address.  For IP Version 4, as specified in RFC 791, the octet string
   MUST contain exactly four octets.  For IP Version 6, as specified in
   RFC 1883, the octet string MUST contain exactly sixteen octets [RFC
   1883].

   When the subjectAltName extension contains a domain name system
   label, the domain name MUST be stored in the dNSName (an IA5String).
   The name MUST be in the "preferred name syntax," as specified by RFC
   1034 [RFC 1034].  Note that while upper and lower case letters are
   allowed in domain names, no signifigance is attached to the case.  In
   addition, while the string " " is a legal domain name, subjectAltName
   extensions with a dNSName of " " MUST NOT be used.  Finally, the use
   of the DNS representation for Internet mail addresses (wpolk.nist.gov
   instead of wpolk@nist.gov) MUST NOT be used; such identities are to
   be encoded as rfc822Name.

   Note: work is currently underway to specify domain names in
   international character sets.  Such names will likely not be
   accommodated by IA5String.  Once this work is complete, this profile
   will be revisited and the appropriate functionality will be added.

   When the subjectAltName extension contains a URI, the name MUST be
   stored in the uniformResourceIdentifier (an IA5String).  The name
   MUST NOT be a relative URL, and it MUST follow the URL syntax and
   encoding rules specified in [RFC 1738].  The name MUST include both a
   scheme (e.g., "http" or "ftp") and a scheme-specific-part.  The
   scheme-specific-part MUST include a fully qualified domain name or IP
   address as the host.

   As specified in [RFC 1738], the scheme name is not case-sensitive
   (e.g., "http" is equivalent to "HTTP").  The host part is also not
   case-sensitive, but other components of the scheme-specific-part may
   be case-sensitive.  When comparing URIs, conforming implementations
   MUST compare the scheme and host without regard to case, but assume
   the remainder of the scheme-specific-part is case sensitive.

   When the subjectAltName extension contains a DN in the directoryName,
   the DN MUST be unique for each subject entity certified by the one CA
   as defined by the issuer name field.  A CA MAY issue more than one
   certificate with the same DN to the same subject entity.

   The subjectAltName MAY carry additional name types through the use of
   the otherName field.  The format and semantics of the name are
   indicated through the OBJECT IDENTIFIER in the type-id field.  The
   name itself is conveyed as value field in otherName.  For example,
   Kerberos [RFC 1510] format names can be encoded into the otherName,
   using using a Kerberos 5 principal name OID and a SEQUENCE of the
   Realm and the PrincipalName.

   Subject 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.

   If the subjectAltName extension is present, the sequence MUST contain
   at least one entry.  Unlike the subject field, conforming CAs MUST
   NOT issue certificates with subjectAltNames containing empty
   GeneralName fields.  For example, an rfc822Name is represented as an
   IA5String.  While an empty string is a valid IA5String, such an
   rfc822Name is not permitted by this profile.  The behavior of clients
   that encounter such a certificate when processing a certificication
   path is not defined by this profile.

   Finally, the semantics of subject alternative names that include
   wildcard characters (e.g., as a placeholder for a set of names) are
   not addressed by this specification.  Applications with specific
   requirements MAY use such names, but they must define the semantics.

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

   SubjectAltName ::= GeneralNames

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

   GeneralName ::= CHOICE {
        otherName                       [0]     OtherName,
        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 }

   OtherName ::= SEQUENCE {
        type-id    OBJECT IDENTIFIER,
        value      [0] EXPLICIT ANY DEFINED BY type-id }

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

4.2.1.8  Issuer Alternative Names

   As with 4.2.1.7, this extension is used to associate Internet style
   identities with the certificate issuer.  Issuer alternative names
   MUST be encoded as in 4.2.1.7.

   Where present, this extension SHOULD NOT 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 used to convey
   identification attributes (e.g., nationality) of the subject.  The
   extension is defined as a sequence of one or more attributes.  This
   extension MUST be 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 the maximum depth of valid certification
   paths that include this certificate.

   The cA boolean indicates whether the certified public key belongs to
   a CA.  If the cA boolean is not asserted, then the keyCertSign bit in
   the key usage extension MUST NOT be asserted.

   The pathLenConstraint field is meaningful only if the cA boolean is
   asserted and the key usage extension asserts the keyCertSign bit
   (section 4.2.1.3).  In this case, it gives the maximum number of non-
   self-issued intermediate certificates that may follow this
   certificate in a valid certification path.  A certificate is self-
   issued if the DNs that appear in the subject and issuer fields are
   identical and are not empty.  (Note: The last certificate in the
   certification path is not an intermediate certificate, and is not
   included in this limit.  Usually, the last certificate is an end
   entity certificate, but it can be a CA certificate.)  A
   pathLenConstraint of zero indicates that only one more certificate
   may follow in a valid certification path.  Where it appears, the
   pathLenConstraint field MUST be greater than or equal to zero.  Where
   pathLenConstraint does not appear, no limit is imposed.

   This extension MUST appear as a critical extension in all CA
   certificates that contain public keys used to validate digital
   signatures on certificates.  This extension MAY appear as a critical
   or non-critical extension in CA certificates that contain public keys
   used exclusively for purposes other than validating digital
   signatures on certificates.  Such CA certificates include ones that
   contain public keys used exclusively for validating digital
   signatures on CRLs and ones that contain key management public keys
   used with certificate enrollment protocols.  This extension MAY
   appear as a critical or non-critical extension in end entity
   certificates.

   CAs MUST NOT include the pathLenConstraint field unless the cA
   boolean is asserted and the key usage extension asserts the
   keyCertSign bit.

   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, which MUST be used only in a CA
   certificate, indicates a name space within which all subject names in
   subsequent certificates in a certification path MUST be located.
   Restrictions apply to the subject distinguished name and apply to
   subject alternative names.  Restrictions apply only when the

   specified name form is present.  If no name of the type is in the
   certificate, the certificate is acceptable.

   Name constraints are not applied to certificates whose issuer and
   subject are identical (unless the certificate is the final
   certificate in the path).  (This could prevent CAs that use name
   constraints from employing self-issued certificates to implement key
   rollover.)

   Restrictions are defined in terms of permitted or excluded name
   subtrees.  Any name matching a restriction in the excludedSubtrees
   field is invalid regardless of information appearing in the
   permittedSubtrees.  This extension MUST be critical.

   Within this profile, the minimum and maximum fields are not used with
   any name forms, thus minimum MUST be zero, and maximum MUST be
   absent.

   For URIs, the constraint applies to the host part of the name.  The
   constraint MAY specify a host or a domain.  Examples would be
   "foo.bar.com";  and ".xyz.com".  When the the constraint begins with
   a period, it MAY be expanded with one or more subdomains.  That is,
   the constraint ".xyz.com" is satisfied by both abc.xyz.com and
   abc.def.xyz.com.  However, the constraint ".xyz.com" is not satisfied
   by "xyz.com".  When the constraint does not begin with a period, it
   specifies a host.

   A name constraint for Internet mail addresses MAY specify a
   particular mailbox, all addresses at a particular host, or all
   mailboxes in a domain.  To indicate a particular mailbox, the
   constraint is the complete mail address.  For example, "root@xyz.com"
   indicates the root mailbox on the host "xyz.com".  To indicate all
   Internet mail addresses on a particular host, the constraint is
   specified as the host name.  For example, the constraint "xyz.com" is
   satisfied by any mail address at the host "xyz.com".  To specify any
   address within a domain, the constraint is specified with a leading
   period (as with URIs).  For example, ".xyz.com" indicates all the
   Internet mail addresses in the domain "xyz.com", but not Internet
   mail addresses on the host "xyz.com".

   DNS name restrictions are expressed as foo.bar.com.  Any DNS name
   that can be constructed by simply adding to the left hand side of the
   name satisfies the name constraint.  For example, www.foo.bar.com
   would satisfy the constraint but foo1.bar.com would not.

   Legacy implementations exist where an RFC 822 name is embedded in the
   subject distinguished name in an attribute of type EmailAddress
   (section 4.1.2.6).  When rfc822 names are constrained, but the

   certificate does not include a subject alternative name, the rfc822
   name constraint MUST be applied to the attribute of type EmailAddress
   in the subject distinguished name.  The ASN.1 syntax for EmailAddress
   and the corresponding OID are supplied in Appendix A.

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

   When applying restrictions of the form directoryName, an
   implementation MUST compare DN attributes.  At a minimum,
   implementations MUST perform the DN comparison rules specified in
   Section 4.1.2.4.  CAs issuing certificates with a restriction of the
   form directoryName SHOULD NOT rely on implementation of the full ISO
   DN name comparison algorithm.  This implies name restrictions MUST be
   stated identically to the encoding used in the subject field or
   subjectAltName extension.

   The syntax of iPAddress MUST be as described in section 4.2.1.7 with
   the following additions specifically for Name Constraints.  For IPv4
   addresses, the ipAddress field of generalName MUST contain eight (8)
   octets, encoded in the style of RFC 1519 (CIDR) to represent an
   address range [RFC 1519].  For IPv6 addresses, the ipAddress field
   MUST contain 32 octets similarly encoded.  For example, a name
   constraint for "class C" subnet 10.9.8.0 is represented as the octets
   0A 09 08 00 FF FF FF 00, representing the CIDR notation
   10.9.8.0/255.255.255.0.

   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 require
   that each certificate in a path contain an acceptable policy
   identifier.

   If the inhibitPolicyMapping field is present, the value indicates the
   number of additional certificates that may appear in the path before
   policy mapping is no longer permitted.  For example, a value of one
   indicates that policy mapping may be processed in certificates issued
   by the subject of this certificate, but not in additional
   certificates in the path.

   If the requireExplicitPolicy field is present, the value of
   requireExplicitPolicy indicates the number of additional certificates
   that may appear in the path before an explicit policy is required for
   the entire path.  When an explicit policy is required, it is
   necessary for all certificates in the path to contain an acceptable
   policy identifier in the certificate policies extension.  An
   acceptable policy identifier is the identifier of a policy required
   by the user of the certification path or the identifier of a policy
   which has been declared equivalent through policy mapping.

   Conforming CAs MUST NOT issue certificates where policy constraints
   is a empty sequence.  That is, at least one of the
   inhibitPolicyMapping field or the requireExplicitPolicy field MUST be
   present.  The behavior of clients that encounter a empty policy
   constraints field is not addressed in this profile.

   This extension MAY be critical or non-critical.

   id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }

   PolicyConstraints ::= SEQUENCE {
        requireExplicitPolicy           [0] SkipCerts OPTIONAL,
        inhibitPolicyMapping            [1] SkipCerts OPTIONAL }

   SkipCerts ::= INTEGER (0..MAX)

4.2.1.13  Extended Key Usage

   This extension indicates one or more purposes for which the certified
   public key may be used, in addition to or in place of the basic
   purposes indicated in the key usage extension.  In general, this
   extension will appear only in end entity certificates.  This
   extension is defined as follows:

   id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }

   ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

   KeyPurposeId ::= OBJECT IDENTIFIER

   Key purposes may be defined by any organization with a need.  Object
   identifiers used to identify key purposes MUST be assigned in
   accordance with IANA or ITU-T Recommendation X.660 [X.660].

   This extension MAY, at the option of the certificate issuer, be
   either critical or non-critical.

   If the extension is present, then the certificate MUST only be used
   for one of the purposes indicated.  If multiple purposes are
   indicated the application need not recognize all purposes indicated,
   as long as the intended purpose is present.  Certificate using
   applications MAY require that a particular purpose be indicated in
   order for the certificate to be acceptable to that application.

   If a CA includes extended key usages to satisfy such applications,
   but does not wish to restrict usages of the key, the CA can include
   the special keyPurposeID anyExtendedKeyUsage.  If the
   anyExtendedKeyUsage keyPurposeID is present, the extension SHOULD NOT
   be critical.

   If a certificate contains both a key usage extension and an extended
   key usage extension, then both extensions MUST be processed
   independently and the certificate MUST only be used for a purpose
   consistent with both extensions.  If there is no purpose consistent
   with both extensions, then the certificate MUST NOT be used for any
   purpose.

   The following key usage purposes are defined:

   anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

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

   id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
   -- TLS WWW server authentication
   -- Key usage bits that may be consistent: digitalSignature,
   -- keyEncipherment or keyAgreement

   id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
   -- TLS WWW client authentication
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or keyAgreement

   id-kp-codeSigning             OBJECT IDENTIFIER ::= { id-kp 3 }
   -- Signing of downloadable executable code
   -- Key usage bits that may be consistent: digitalSignature

   id-kp-emailProtection         OBJECT IDENTIFIER ::= { id-kp 4 }
   -- E-mail protection
   -- Key usage bits that may be consistent: digitalSignature,
   -- nonRepudiation, and/or (keyEncipherment or keyAgreement)

   id-kp-timeStamping            OBJECT IDENTIFIER ::= { id-kp 8 }
   -- Binding the hash of an object to a time
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or nonRepudiation

   id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }
   -- Signing OCSP responses
   -- Key usage bits that may be consistent: digitalSignature
   -- and/or nonRepudiation

4.2.1.14  CRL Distribution Points

   The CRL distribution points extension identifies how CRL information
   is obtained.  The extension SHOULD 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.

   The cRLDistributionPoints extension is a SEQUENCE of
   DistributionPoint.  A DistributionPoint consists of three fields,
   each of which is optional: distributionPoint, reasons, and cRLIssuer.
   While each of these fields is optional, a DistributionPoint MUST NOT
   consist of only the reasons field; either distributionPoint or
   cRLIssuer MUST be present.  If the certificate issuer is not the CRL
   issuer, then the cRLIssuer field MUST be present and contain the Name
   of the CRL issuer.  If the certificate issuer is also the CRL issuer,
   then the cRLIssuer field MUST be omitted and the distributionPoint
   field MUST be present.  If the distributionPoint field is omitted,
   cRLIssuer MUST be present and include a Name corresponding to an
   X.500 or LDAP directory entry where the CRL is located.

   When the distributionPoint field is present, it contains either a
   SEQUENCE of general names or a single value, nameRelativeToCRLIssuer.
   If the cRLDistributionPoints extension contains a general name of
   type URI, the following semantics MUST be assumed: the URI is a
   pointer to the current CRL for the associated reasons and will be
   issued by the associated cRLIssuer.  The expected values for the URI
   are those defined in 4.2.1.7.  Processing rules for other values are
   not defined by this specification.

   If the DistributionPointName contains multiple values, each name
   describes a different mechanism to obtain the same CRL.  For example,
   the same CRL could be available for retrieval through both LDAP and
   HTTP.

   If the DistributionPointName contains the single value
   nameRelativeToCRLIssuer, the value provides a distinguished name
   fragment.  The fragment is appended to the X.500 distinguished name
   of the CRL issuer to obtain the distribution point name.  If the
   cRLIssuer field in the DistributionPoint is present, then the name
   fragment is appended to the distinguished name that it contains;
   otherwise, the name fragment is appended to the certificate issuer
   distinguished name.  The DistributionPointName MUST NOT use the
   nameRealtiveToCRLIssuer alternative when cRLIssuer contains more than
   one distinguished name.

   If the DistributionPoint omits the reasons field, the CRL MUST
   include revocation information for all reasons.

   The cRLIssuer identifies the entity who signs and issues the CRL.  If
   present, the cRLIssuer MUST contain at least one an X.500
   distinguished name (DN), and MAY also contain other name forms.
   Since the cRLIssuer is compared to the CRL issuer name, the X.501
   type Name MUST follow the encoding rules for the issuer name field in
   the certificate (section 4.1.2.4).

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

   CRLDistributionPoints ::= 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),
        privilegeWithdrawn      (7),
        aACompromise            (8) }

4.2.1.15  Inhibit Any-Policy

   The inhibit any-policy extension can be used in certificates issued
   to CAs.  The inhibit any-policy indicates that the special anyPolicy
   OID, with the value { 2 5 29 32 0 }, is not considered an explicit
   match for other certificate policies.  The value indicates the number
   of additional certificates that may appear in the path before
   anyPolicy is no longer permitted.  For example, a value of one
   indicates that anyPolicy may be processed in certificates issued by
   the subject of this certificate, but not in additional certificates
   in the path.

   This extension MUST be critical.

   id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }

   InhibitAnyPolicy ::= SkipCerts

   SkipCerts ::= INTEGER (0..MAX)

4.2.1.16  Freshest CRL (a.k.a. Delta CRL Distribution Point)

   The freshest CRL extension identifies how delta CRL information is
   obtained.  The extension MUST be non-critical.  Further discussion of
   CRL management is contained in section 5.

   The same syntax is used for this extension and the
   cRLDistributionPoints extension, and is described in section
   4.2.1.14.  The same conventions apply to both extensions.

   id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

   FreshestCRL ::= CRLDistributionPoints

4.2.2  Private Internet Extensions

   This section defines two extensions for use in the Internet Public
   Key Infrastructure.  These extensions may be used to direct
   applications to on-line information about the issuing CA or the
   subject.  As the information may be available in multiple forms, each
   extension is a sequence of IA5String values, each of which represents
   a URI.  The URI implicitly specifies the location and format of the
   information and the method for obtaining the information.

   An object identifier is defined for the private extension.  The
   object identifier associated with the private extension is defined
   under the arc id-pe within the arc id-pkix.  Any future extensions
   defined for the Internet PKI are also expected to be defined under
   the arc id-pe.

      id-pkix  OBJECT IDENTIFIER  ::=
               { iso(1) identified-organization(3) dod(6) internet(1)
                       security(5) mechanisms(5) pkix(7) }

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

4.2.2.1  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 may include on-line
   validation services and CA policy data.  (The location of CRLs is not
   specified in this extension; that information is provided by the
   cRLDistributionPoints extension.)  This extension may be included in
   end entity or CA certificates, and it MUST be non-critical.

   id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

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

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

   id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

   id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 }

   id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }

   Each entry in the sequence AuthorityInfoAccessSyntax describes the
   format and location of additional information provided by the CA that
   issued the certificate in which this extension appears.  The type and
   format of the information is specified by the accessMethod field; the
   accessLocation field specifies the location of the information.  The
   retrieval mechanism may be implied by the accessMethod or specified
   by accessLocation.

   This profile defines two accessMethod OIDs: id-ad-caIssuers and
   id-ad-ocsp.

   The id-ad-caIssuers OID is used when the additional information lists
   CAs that have issued certificates superior to the CA that issued the
   certificate containing this extension.  The referenced CA issuers
   description is intended to aid certificate users in the selection of
   a certification path that terminates at a point trusted by the
   certificate user.

   When id-ad-caIssuers appears as accessMethod, the accessLocation
   field describes the referenced description server and the access
   protocol to obtain the referenced description.  The accessLocation
   field is defined as a GeneralName, which can take several forms.
   Where the information is available via http, ftp, or ldap,
   accessLocation MUST be a uniformResourceIdentifier.  Where the
   information is available via the Directory Access Protocol (DAP),
   accessLocation MUST be a directoryName.  The entry for that
   directoryName contains CA certificates in the crossCertificatePair
   attribute.  When the information is available via electronic mail,
   accessLocation MUST be an rfc822Name.  The semantics of other
   id-ad-caIssuers accessLocation name forms are not defined.

   The id-ad-ocsp OID is used when revocation information for the
   certificate containing this extension is available using the Online
   Certificate Status Protocol (OCSP) [RFC 2560].

   When id-ad-ocsp appears as accessMethod, the accessLocation field is
   the location of the OCSP responder, using the conventions defined in
   [RFC 2560].

   Additional access descriptors may be defined in other PKIX
   specifications.

4.2.2.2  Subject Information Access

   The subject information access extension indicates how to access
   information and services for the subject of the certificate in which
   the extension appears.  When the subject is a CA, information and
   services may include certificate validation services and CA policy

   data.  When the subject is an end entity, the information describes
   the type of services offered and how to access them.  In this case,
   the contents of this extension are defined in the protocol
   specifications for the suported services.  This extension may be
   included in subject or CA certificates, and it MUST be non-critical.

   id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

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

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

   Each entry in the sequence SubjectInfoAccessSyntax describes the
   format and location of additional information provided by the subject
   of the certificate in which this extension appears.  The type and
   format of the information is specified by the accessMethod field; the
   accessLocation field specifies the location of the information.  The
   retrieval mechanism may be implied by the accessMethod or specified
   by accessLocation.

   This profile defines one access method to be used when the subject is
   a CA, and one access method to be used when the subject is an end
   entity.  Additional access methods may be defined in the future in
   the protocol specifications for other services.

   The id-ad-caRepository OID is used when the subject is a CA, and
   publishes its certificates and CRLs (if issued) in a repository.  The
   accessLocation field is defined as a GeneralName, which can take
   several forms.  Where the information is available via http, ftp, or
   ldap, accessLocation MUST be a uniformResourceIdentifier.  Where the
   information is available via the directory access protocol (dap),
   accessLocation MUST be a directoryName.  When the information is
   available via electronic mail, accessLocation MUST be an rfc822Name.
   The semantics of other name forms of of accessLocation (when
   accessMethod is id-ad-caRepository) are not defined by this
   specification.

   The id-ad-timeStamping OID is used when the subject offers
   timestamping services using the Time Stamp Protocol defined in
   [PKIXTSA].  Where the timestamping services are available via http or
   ftp, accessLocation MUST be a uniformResourceIdentifier.  Where the
   timestamping services are available via electronic mail,
   accessLocation MUST be an rfc822Name.  Where timestamping services

   are available using TCP/IP, the dNSName or ipAddress name forms may
   be used.  The semantics of other name forms of accessLocation (when
   accessMethod is id-ad-timeStamping) are not defined by this
   specification.

   Additional access descriptors may be defined in other PKIX
   specifications.

   id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

   id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

   id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }

5  CRL and CRL Extensions Profile

   As discussed 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.  The profile defines a set of
   information that can be expected in every CRL.  Also, the profile
   defines common locations within the CRL for frequently used
   attributes as well as common representations for these attributes.

   CRL issuers issue CRLs.  In general, the CRL issuer is the CA.  CAs
   publish CRLs to provide status information about the certificates
   they issued.  However, a CA may delegate this responsibility to
   another trusted authority.  Whenever the CRL issuer is not the CA
   that issued the certificates, the CRL is referred to as an indirect
   CRL.

   Each CRL has a particular scope.  The CRL scope is the set of
   certificates that could appear on a given CRL.  For example, the
   scope could be "all certificates issued by CA X", "all CA
   certificates issued by CA X", "all certificates issued by CA X that
   have been revoked for reasons of key compromise and CA compromise",
   or could be a set of certificates based on arbitrary local
   information, such as "all certificates issued to the NIST employees
   located in Boulder".

   A complete CRL lists all unexpired certificates, within its scope,
   that have been revoked for one of the revocation reasons covered by
   the CRL scope.  The CRL issuer MAY also generate delta CRLs.  A delta
   CRL only lists those certificates, within its scope, whose revocation
   status has changed since the issuance of a referenced complete CRL.
   The referenced complete CRL is referred to as a base CRL.  The scope
   of a delta CRL MUST be the same as the base CRL that it references.

   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
   certificate status mechanisms are provided.  When CRLs are issued,
   the CRLs MUST be version 2 CRLs, include the date by which the next
   CRL will be issued in the nextUpdate field (section 5.1.2.5), include
   the CRL number extension (section 5.2.3), and include the authority
   key identifier extension (section 5.2.1).  Conforming applications
   that support CRLs are REQUIRED to process both version 1 and version
   2 complete CRLs that provide revocation information for all
   certificates issued by one CA.  Conforming applications are NOT
   REQUIRED to support processing of delta CRLs, indirect CRLs, or CRLs
   with a scope other than all certificates issued by one CA.

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,
        signatureValue       BIT STRING  }

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

   -- Version, Time, CertificateSerialNumber, and Extensions
   -- are all defined in the ASN.1 in section 4.1

   -- AlgorithmIdentifier is defined in section 4.1.1.2

   The following items describe the 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 described in detail in the following subsections.

5.1.1.1  tbsCertList

   The first field in the sequence is the tbsCertList.  This field is
   itself a sequence containing the name of the issuer, issue date,
   issue date of the next list, the optional list of revoked
   certificates, and optional CRL extensions.  When there are no revoked
   certificates, the revoked certificates list is absent.  When one or
   more certificates are revoked, each entry on the revoked certificate
   list is defined by a sequence of user certificate serial number,
   revocation date, and optional CRL entry extensions.

5.1.1.2  signatureAlgorithm

   The signatureAlgorithm field contains the algorithm identifier for
   the algorithm used by the CRL issuer to sign the CertificateList.
   The field is of type AlgorithmIdentifier, which is defined in section
   4.1.1.2.  [PKIXALGS] lists the supported algorithms for this
   specification, but other signature algorithms MAY also be supported.

   This field MUST contain the same algorithm identifier as the
   signature field in the sequence tbsCertList (section 5.1.2.2).

5.1.1.3  signatureValue

   The signatureValue field contains a digital signature computed upon
   the ASN.1 DER encoded tbsCertList.  The ASN.1 DER encoded tbsCertList
   is used as the input to the signature function.  This signature value
   is encoded as a BIT STRING and included in the CRL signatureValue
   field.  The details of this process are specified for each of the
   supported algorithms in [PKIXALGS].

   CAs that are also CRL issuers MAY use one private key to digitally
   sign certificates and CRLs, or MAY use separate private keys to
   digitally sign certificates and CRLs.  When separate private keys are
   employed, each of the public keys associated with these private keys
   is placed in a separate certificate, one with the keyCertSign bit set
   in the key usage extension, and one with the cRLSign bit set in the
   key usage extension (section 4.2.1.3).  When separate private keys
   are employed, certificates issued by the CA contain one authority key
   identifier, and the corresponding CRLs contain a different authority
   key identifier.  The use of separate CA certificates for validation
   of certificate signatures and CRL signatures can offer improved
   security characteristics; however, it imposes a burden on
   applications, and it might limit interoperability.  Many applications
   construct a certification path, and then validate the certification
   path (section 6).  CRL checking in turn requires a separate
   certification path to be constructed and validated for the CA's CRL
   signature validation certificate.  Applications that perform CRL
   checking MUST support certification path validation when certificates
   and CRLs are digitally signed with the same CA private key.  These
   applications SHOULD support certification path validation when
   certificates and CRLs are digitally signed with different CA private
   keys.

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 CRL issuer will issue
   the next CRL.

   Optional fields include lists of revoked certificates and CRL
   extensions.  The revoked certificate list is optional to support the
   case where a CA has not revoked any unexpired certificates that it

   has issued.  The profile requires conforming CRL issuers to use the
   CRL number and authority key identifier CRL extensions in all CRLs
   issued.

5.1.2.1  Version

   This optional field describes the version of the encoded CRL.  When
   extensions are used, as required by this profile, this field MUST be
   present and MUST specify version 2 (the integer value is 1).

5.1.2.2  Signature

   This field contains the algorithm identifier for the algorithm used
   to sign the CRL.  [PKIXALGS] lists OIDs for the most popular
   signature algorithms used in the Internet PKI.

   This field MUST contain the same algorithm identifier as the
   signatureAlgorithm field in the sequence CertificateList (section
   5.1.1.2).

5.1.2.3  Issuer Name

   The issuer name identifies the entity who has signed and issued the
   CRL.  The issuer identity is carried in the issuer name field.
   Alternative name forms may also appear in the issuerAltName extension
   (section 5.2.2).  The issuer name field MUST contain an X.500
   distinguished name (DN).  The issuer name field is defined as the
   X.501 type Name, and MUST follow the encoding rules for the issuer
   name field in the certificate (section 4.1.2.4).

5.1.2.4  This Update

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

   CRL issuers conforming to this profile MUST encode thisUpdate as
   UTCTime for dates through the year 2049.  CRL issuers conforming to
   this profile MUST encode thisUpdate as GeneralizedTime for dates in
   the year 2050 or later.

   Where encoded as UTCTime, thisUpdate MUST be specified and
   interpreted as defined in section 4.1.2.5.1.  Where encoded as
   GeneralizedTime, thisUpdate MUST 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.  CRL issuers SHOULD
   issue CRLs with a nextUpdate time equal to or later than all previous
   CRLs.  nextUpdate may be encoded as UTCTime or GeneralizedTime.

   This profile requires inclusion of nextUpdate in all CRLs issued by
   conforming CRL issuers.  Note that the ASN.1 syntax of TBSCertList
   describes this field as OPTIONAL, which is consistent with the ASN.1
   structure defined in [X.509].  The behavior of clients processing
   CRLs which omit nextUpdate is not specified by this profile.

   CRL issuers conforming to this profile MUST encode nextUpdate as
   UTCTime for dates through the year 2049.  CRL issuers conforming to
   this profile MUST encode nextUpdate as GeneralizedTime for dates in
   the year 2050 or later.

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

5.1.2.6  Revoked Certificates

   When there are no revoked certificates, the revoked certificates list
   MUST be absent.  Otherwise, revoked certificates are listed by their
   serial numbers.  Certificates revoked by the CA are uniquely
   identified by the certificate serial number.  The date on which the
   revocation occurred is specified.  The time for revocationDate MUST
   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.

5.1.2.7  Extensions

   This field may only appear if the version is 2 (section 5.1.2.1).  If
   present, this field is a sequence of one or more CRL extensions.  CRL
   extensions are discussed in section 5.2.

5.2  CRL Extensions

   The extensions defined by ANSI X9, ISO/IEC, and ITU-T for X.509 v2
   CRLs [X.509] [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 a critical extension which it does not know how to
   process.  However, an unrecognized non-critical extension may be
   ignored.  The following subsections present 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 CRL issuers are REQUIRED to include the authority key
   identifier (section 5.2.1) and the CRL number (section 5.2.3)
   extensions in all CRLs issued.

5.2.1  Authority Key Identifier

   The authority key identifier extension provides a means of
   identifying the public key corresponding to the private 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.  This extension
   is especially useful where an issuer has more than one signing key,
   either due to multiple concurrent key pairs or due to changeover.

   Conforming CRL issuers MUST use the key identifier method, and MUST
   include this extension in all CRLs issued.

   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
   alternative name extension MUST be used; however, a DNS name MAY be
   represented in the issuer field using the domainComponent attribute
   as described in section 4.1.2.4.

   The issuerAltName extension SHOULD NOT be marked critical.

   The OID 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 increasing sequence number for a given CRL scope and
   CRL issuer.  This extension allows users to easily determine when a
   particular CRL supersedes another CRL.  CRL numbers also support the
   identification of complementary complete CRLs and delta CRLs.  CRL
   issuers conforming to this profile MUST include this extension in all
   CRLs.

   If a CRL issuer generates delta CRLs in addition to complete CRLs for
   a given scope, the complete CRLs and delta CRLs MUST share one
   numbering sequence.  If a delta CRL and a complete CRL that cover the
   same scope are issued at the same time, they MUST have the same CRL
   number and provide the same revocation information.  That is, the
   combination of the delta CRL and an acceptable complete CRL MUST
   provide the same revocation information as the simultaneously issued
   complete CRL.

   If a CRL issuer generates two CRLs (two complete CRLs, two delta
   CRLs, or a complete CRL and a delta CRL) for the same scope at
   different times, the two CRLs MUST NOT have the same CRL number.
   That is, if the this update field (section 5.1.2.4) in the two CRLs
   are not identical, the CRL numbers MUST be different.

   Given the requirements above, CRL numbers can be expected to contain
   long integers.  CRL verifiers MUST be able to handle CRLNumber values
   up to 20 octets.  Conformant CRL issuers MUST NOT use CRLNumber
   values longer than 20 octets.

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

   CRLNumber ::= INTEGER (0..MAX)

5.2.4  Delta CRL Indicator

   The delta CRL indicator is a critical CRL extension that identifies a
   CRL as being a delta CRL.  Delta CRLs contain updates to revocation
   information previously distributed, rather than all the information
   that would appear in a complete CRL.  The use of delta CRLs can
   significantly reduce network load and processing time in some
   environments.  Delta CRLs are generally smaller than the CRLs they
   update, so applications that obtain delta CRLs consume less network
   bandwidth than applications that obtain the corresponding complete
   CRLs.  Applications which store revocation information in a format
   other than the CRL structure can add new revocation information to
   the local database without reprocessing information.

   The delta CRL indicator extension contains the single value of type
   BaseCRLNumber.  The CRL number identifies the CRL, complete for a
   given scope, that was used as the starting point in the generation of
   this delta CRL.  A conforming CRL issuer MUST publish the referenced
   base CRL as a complete CRL.  The delta CRL contains all updates to
   the revocation status for that same scope.  The combination of a
   delta CRL plus the referenced base CRL is equivalent to a complete
   CRL, for the applicable scope, at the time of publication of the
   delta CRL.

   When a conforming CRL issuer generates a delta CRL, the delta CRL
   MUST include a critical delta CRL indicator extension.

   When a delta CRL is issued, it MUST cover the same set of reasons and
   the same set of certificates that were covered by the base CRL it
   references.  That is, the scope of the delta CRL MUST be the same as
   the scope of the complete CRL referenced as the base.  The referenced
   base CRL and the delta CRL MUST omit the issuing distribution point
   extension or contain identical issuing distribution point extensions.
   Further, the CRL issuer MUST use the same private key to sign the
   delta CRL and any complete CRL that it can be used to update.

   An application that supports delta CRLs can construct a CRL that is
   complete for a given scope by combining a delta CRL for that scope
   with either an issued CRL that is complete for that scope or a
   locally constructed CRL that is complete for that scope.

   When a delta CRL is combined with a complete CRL or a locally
   constructed CRL, the resulting locally constructed CRL has the CRL
   number specified in the CRL number extension found in the delta CRL
   used in its construction.  In addition, the resulting locally
   constructed CRL has the thisUpdate and nextUpdate times specified in
   the corresponding fields of the delta CRL used in its construction.
   In addition, the locally constructed CRL inherits the issuing
   distribution point from the delta CRL.

   A complete CRL and a delta CRL MAY be combined if the following four
   conditions are satisfied:

      (a)  The complete CRL and delta CRL have the same issuer.

      (b)  The complete CRL and delta CRL have the same scope.  The two
      CRLs have the same scope if either of the following conditions are
      met:

         (1)  The issuingDistributionPoint extension is omitted from
         both the complete CRL and the delta CRL.

         (2)  The issuingDistributionPoint extension is present in both
         the complete CRL and the delta CRL, and the values for each of
         the fields in the extensions are the same in both CRLs.

      (c)  The CRL number of the complete CRL is equal to or greater
      than the BaseCRLNumber specified in the delta CRL.  That is, the
      complete CRL contains (at a minimum) all the revocation
      information held by the referenced base CRL.

      (d)  The CRL number of the complete CRL is less than the CRL
      number of the delta CRL.  That is, the delta CRL follows the
      complete CRL in the numbering sequence.

   CRL issuers MUST ensure that the combination of a delta CRL and any
   appropriate complete CRL accurately reflects the current revocation
   status.  The CRL issuer MUST include an entry in the delta CRL for
   each certificate within the scope of the delta CRL whose status has
   changed since the generation of the referenced base CRL:

      (a)  If the certificate is revoked for a reason included in the
      scope of the CRL, list the certificate as revoked.

      (b)  If the certificate is valid and was listed on the referenced
      base CRL or any subsequent CRL with reason code certificateHold,
      and the reason code certificateHold is included in the scope of
      the CRL, list the certificate with the reason code removeFromCRL.

      (c)  If the certificate is revoked for a reason outside the scope
      of the CRL, but the certificate was listed on the referenced base
      CRL or any subsequent CRL with a reason code included in the scope
      of this CRL, list the certificate as revoked but omit the reason
      code.

      (d)  If the certificate is revoked for a reason outside the scope
      of the CRL and the certificate was neither listed on the
      referenced base CRL nor any subsequent CRL with a reason code
      included in the scope of this CRL, do not list the certificate on
      this CRL.

   The status of a certificate is considered to have changed if it is
   revoked, placed on hold, released from hold, or if its revocation
   reason changes.

   It is appropriate to list a certificate with reason code
   removeFromCRL on a delta CRL even if the certificate was not on hold
   in the referenced base CRL.  If the certificate was placed on hold in

   any CRL issued after the base but before this delta CRL and then
   released from hold, it MUST be listed on the delta CRL with
   revocation reason removeFromCRL.

   A CRL issuer MAY optionally list a certificate on a delta CRL with
   reason code removeFromCRL if the notAfter time specified in the
   certificate precedes the thisUpdate time specified in the delta CRL
   and the certificate was listed on the referenced base CRL or in any
   CRL issued after the base but before this delta CRL.

   If a certificate revocation notice first appears on a delta CRL, then
   it is possible for the certificate validity period to expire before
   the next complete CRL for the same scope is issued.  In this case,
   the revocation notice MUST be included in all subsequent delta CRLs
   until the revocation notice is included on at least one explicitly
   issued complete CRL for this scope.

   An application that supports delta CRLs MUST be able to construct a
   current complete CRL by combining a previously issued complete CRL
   and the most current delta CRL.  An application that supports delta
   CRLs MAY also be able to construct a current complete CRL by
   combining a previously locally constructed complete CRL and the
   current delta CRL.  A delta CRL is considered to be the current one
   if the current time is between the times contained in the thisUpdate
   and nextUpdate fields.  Under some circumstances, the CRL issuer may
   publish one or more delta CRLs before indicated by the nextUpdate
   field.  If more than one current delta CRL for a given scope is
   encountered, the application SHOULD consider the one with the latest
   value in thisUpdate to be the most current one.

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

   BaseCRLNumber ::= CRLNumber

5.2.5  Issuing Distribution Point

   The issuing distribution point is a critical CRL extension that
   identifies the CRL distribution point and scope for a particular CRL,
   and it indicates whether the CRL covers revocation for end entity
   certificates only, CA certificates only, attribute certificates only,

   or a limited set of reason codes.  Although the extension is
   critical, conforming implementations are not required to support this
   extension.

   The CRL is signed using the CRL issuer'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
   than the Directory entry of the CRL issuer.

   The reason codes associated with a distribution point MUST be
   specified in onlySomeReasons.  If onlySomeReasons does not appear,
   the distribution point MUST contain revocations for all reason codes.
   CAs may use CRL distribution points to partition the CRL on the basis
   of compromise and routine revocation.  In this case, the revocations
   with reason code keyCompromise (1), cACompromise (2), and
   aACompromise (8) appear in one distribution point, and the
   revocations with other reason codes appear in another distribution
   point.

   If the distributionPoint field is present and contains a URI, the
   following semantics MUST be assumed: the object is a pointer to the
   most current CRL issued by this CRL issuer.  The URI schemes ftp,
   http, mailto [RFC1738] and ldap [RFC1778] are defined for this
   purpose.  The URI MUST be an absolute pathname, not a relative
   pathname, and MUST specify the host.

   If the distributionPoint field is absent, the CRL MUST contain
   entries for all revoked unexpired certificates issued by the CRL
   issuer, if any, within the scope of the CRL.

   The CRL issuer MUST assert the indirectCRL boolean, if the scope of
   the CRL includes certificates issued by authorities other than the
   CRL issuer.  The authority responsible for each entry is indicated by
   the certificate issuer CRL entry extension (section 5.3.4).

   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,
        onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

5.2.6  Freshest CRL (a.k.a. Delta CRL Distribution Point)

   The freshest CRL extension identifies how delta CRL information for
   this complete CRL is obtained.  The extension MUST be non-critical.
   This extension MUST NOT appear in delta CRLs.

   The same syntax is used for this extension as the
   cRLDistributionPoints certificate extension, and is described in
   section 4.2.1.14.  However, only the distribution point field is
   meaningful in this context.  The reasons and CRLIssuer fields MUST be
   omitted from this CRL extension.

   Each distribution point name provides the location at which a delta
   CRL for this complete CRL can be found.  The scope of these delta
   CRLs MUST be the same as the scope of this complete CRL.  The
   contents of this CRL extension are only used to locate delta CRLs;
   the contents are not used to validate the CRL or the referenced delta
   CRLs.  The encoding conventions defined for distribution points in
   section 4.2.1.14 apply to this extension.

   id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

   FreshestCRL ::= CRLDistributionPoints

5.3  CRL Entry Extensions

   The CRL entry extensions defined by ISO/IEC, ITU-T, and ANSI X9 for
   X.509 v2 CRLs provide methods for associating additional attributes
   with CRL entries [X.509] [X9.55].  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
   subsections present 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 used in this specification are non-critical.
   Support for these extensions is optional for conforming CRL issuers
   and applications.  However, CRL issuers SHOULD include reason codes
   (section 5.3.1) and invalidity dates (section 5.3.3) 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.  CRL issuers are strongly
   encouraged to include meaningful 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),
        privilegeWithdrawn      (9),
        aACompromise           (10) }

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 MUST recognize the following
   instruction codes.

   holdInstruction    OBJECT IDENTIFIER ::=
                    { 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 an id-holdinstruction-
   callissuer MUST call the certificate issuer or reject the
   certificate.  Conforming applications which encounter an id-
   holdinstruction-reject MUST reject the certificate.  The hold
   instruction id-holdinstruction-none is semantically equivalent to the
   absence of a holdInstructionCode, and its use is strongly deprecated
   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,
   which is the date at which the CA processed the revocation.  When a
   revocation is first posted by a CRL issuer in a CRL, the invalidity
   date may precede the date of issue of earlier CRLs, but the
   revocation date SHOULD NOT precede the date of issue of earlier CRLs.
   Whenever this information is available, CRL issuers are strongly
   encouraged to share it with CRL users.

   The GeneralizedTime values included in this field MUST be expressed
   in Greenwich Mean Time (Zulu), and MUST be specified and interpreted
   as defined in section 4.1.2.5.2.

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

   invalidityDate ::=  GeneralizedTime

5.3.4  Certificate Issuer

   This CRL entry extension identifies the certificate issuer associated
   with an entry in an indirect CRL, that is, a CRL that has the
   indirectCRL indicator set in its issuing distribution point
   extension.  If this extension is not present on the first entry in an
   indirect CRL, the certificate issuer defaults to the CRL issuer.  On
   subsequent entries in an indirect CRL, if this extension is not
   present, the certificate issuer for the entry is the same as that for
   the preceding entry.  This field is defined as follows:

   id-ce-certificateIssuer   OBJECT IDENTIFIER ::= { id-ce 29 }

   certificateIssuer ::=     GeneralNames

   If used by conforming CRL issuers, this extension MUST always be
   critical.  If an implementation ignored this extension it could not
   correctly attribute CRL entries to certificates.  This specification
   RECOMMENDS that implementations recognize this extension.

6  Certification Path Validation

   Certification path validation procedures for the Internet PKI are
   based on the algorithm supplied in [X.509].  Certification path
   processing verifies the binding between the subject distinguished
   name and/or subject alternative name and subject public key.  The
   binding is limited by constraints which are specified in the

   certificates which comprise the path and inputs which are specified
   by the relying party.  The basic constraints and policy constraints
   extensions allow the certification path processing logic to automate
   the decision making process.

   This section describes an algorithm for validating certification
   paths.  Conforming implementations of this specification are not
   required to implement this algorithm, but MUST provide functionality
   equivalent to the external behavior resulting from this procedure.
   Any algorithm may be used by a particular implementation so long as
   it derives the correct result.

   In section 6.1, the text describes basic path validation.  Valid
   paths begin with certificates issued by a trust anchor.  The
   algorithm requires the public key of the CA, the CA's name, and any
   constraints upon the set of paths which may be validated using this
   key.

   The selection of a trust anchor is a matter of policy: it could be
   the top CA in a hierarchical PKI; the CA that issued the verifier's
   own certificate(s); or any other CA in a network PKI.  The path
   validation procedure is the same regardless of the choice of trust
   anchor.  In addition, different applications may rely on different
   trust anchor, or may accept paths that begin with any of a set of
   trust anchor.

   Section 6.2 describes methods for using the path validation algorithm
   in specific implementations.  Two specific cases are discussed: the
   case where paths may begin with one of several trusted CAs; and where
   compatibility with the PEM architecture is required.

   Section 6.3 describes the steps necessary to determine if a
   certificate is revoked or on hold status when CRLs are the revocation
   mechanism used by the certificate issuer.

6.1  Basic Path Validation

   This text describes an algorithm for X.509 path processing.  A
   conformant implementation MUST include an X.509 path processing
   procedure that is functionally equivalent to the external behavior of
   this algorithm.  However, support for some of the certificate
   extensions processed in this algorithm are OPTIONAL for compliant
   implementations.  Clients that do not support these extensions MAY
   omit the corresponding steps in the path validation algorithm.

   For example, clients are NOT REQUIRED to support the policy mapping
   extension.  Clients that do not support this extension MAY omit the
   path validation steps where policy mappings are processed.  Note that
   clients MUST reject the certificate if it contains an unsupported
   critical extension.

   The algorithm presented in this section validates the certificate
   with respect to the current date and time.  A conformant
   implementation MAY also support validation with respect to some point
   in the past.  Note that mechanisms are not available for validating a
   certificate with respect to a time outside the certificate validity
   period.

   The trust anchor is an input to the algorithm.  There is no
   requirement that the same trust anchor be used to validate all
   certification paths.  Different trust anchors MAY be used to validate
   different paths, as discussed further in Section 6.2.

   The primary goal of path validation is to verify the binding between
   a subject distinguished name or a subject alternative name and
   subject public key, as represented in the end entity certificate,
   based on the public key of the trust anchor.  This requires obtaining
   a sequence of certificates that support that binding.  The procedure
   performed to obtain this sequence of certificates is outside the
   scope of this specification.

   To meet this goal, the path validation process verifies, among other
   things, that a prospective certification path (a sequence of n
   certificates) satisfies the following conditions:

      (a)  for all x in {1, ..., n-1}, the subject of certificate x is
      the issuer of certificate x+1;

      (b)  certificate 1 is issued by the trust anchor;

      (c)  certificate n is the certificate to be validated; and

      (d)  for all x in {1, ..., n}, the certificate was valid at the
      time in question.

   When the trust anchor is provided in the form of a self-signed
   certificate, this self-signed certificate is not included as part of
   the prospective certification path.  Information about trust anchors
   are provided as inputs to the certification path validation algorithm
   (section 6.1.1).

   A particular certification path may not, however, be appropriate for
   all applications.  Therefore, an application MAY augment this
   algorithm to further limit the set of valid paths.  The path
   validation process also determines the set of certificate policies
   that are valid for this path, based on the certificate policies
   extension, policy mapping extension, policy constraints extension,
   and inhibit any-policy extension.  To achieve this, the path
   validation algorithm constructs a valid policy tree.  If the set of
   certificate policies that are valid for this path is not empty, then
   the result will be a valid policy tree of depth n, otherwise the
   result will be a null valid policy tree.

   A certificate is self-issued if the DNs that appear in the subject
   and issuer fields are identical and are not empty.  In general, the
   issuer and subject of the certificates that make up a path are
   different for each certificate.  However, a CA may issue a
   certificate to itself to support key rollover or changes in
   certificate policies.  These self-issued certificates are not counted
   when evaluating path length or name constraints.

   This section presents the algorithm in four basic steps: (1)
   initialization, (2) basic certificate processing, (3) preparation for
   the next certificate, and (4) wrap-up.  Steps (1) and (4) are
   performed exactly once.  Step (2) is performed for all certificates
   in the path.  Step (3) is performed for all certificates in the path
   except the final certificate.  Figure 2 provides a high-level
   flowchart of this algorithm.

                           +-------+
                           | START |
                           +-------+
                               |
                               V
                       +----------------+
                       | Initialization |
                       +----------------+
                               |
                               +<--------------------+
                               |                     |
                               V                     |
                       +----------------+            |
                       |  Process Cert  |            |
                       +----------------+            |
                               |                     |
                               V                     |
                       +================+            |
                       |  IF Last Cert  |            |
                       |    in Path     |            |
                       +================+            |
                         |            |              |
                    THEN |            | ELSE         |
                         V            V              |
              +----------------+ +----------------+  |
              |    Wrap up     | |  Prepare for   |  |
              +----------------+ |   Next Cert    |  |
                      |          +----------------+  |
                      V               |              |
                  +-------+           +--------------+
                  | STOP  |
                  +-------+

         Figure 2.  Certification Path Processing Flowchart

6.1.1  Inputs

   This algorithm assumes the following seven inputs are provided to the
   path processing logic:

      (a)  a prospective certification path of length n.

      (b)  the current date/time.

      (c)  user-initial-policy-set:  A set of certificate policy
      identifiers naming the policies that are acceptable to the
      certificate user.  The user-initial-policy-set contains the
      special value any-policy if the user is not concerned about
      certificate policy.

      (d)  trust anchor information, describing a CA that serves as a
      trust anchor for the certification path.  The trust anchor
      information includes:

         (1)  the trusted issuer name,

         (2)  the trusted public key algorithm,

         (3)  the trusted public key, and

         (4)  optionally, the trusted public key parameters associated
         with the public key.

      The trust anchor information may be provided to the path
      processing procedure in the form of a self-signed certificate.
      The trusted anchor information is trusted because it was delivered
      to the path processing procedure by some trustworthy out-of-band
      procedure.  If the trusted public key algorithm requires
      parameters, then the parameters are provided along with the
      trusted public key.

      (e) initial-policy-mapping-inhibit, which indicates if policy
      mapping is allowed in the certification path.

      (f) initial-explicit-policy, which indicates if the path must be
      valid for at least one of the certificate policies in the user-
      initial-policy-set.

      (g) initial-any-policy-inhibit, which indicates whether the
      anyPolicy OID should be processed if it is included in a
      certificate.

6.1.2  Initialization

   This initialization phase establishes eleven state variables based
   upon the seven inputs:

      (a)  valid_policy_tree:  A tree of certificate policies with their
      optional qualifiers; each of the leaves of the tree represents a
      valid policy at this stage in the certification path validation.
      If valid policies exist at this stage in the certification path
      validation, the depth of the tree is equal to the number of

      certificates in the chain that have been processed.  If valid
      policies do not exist at this stage in the certification path
      validation, the tree is set to NULL.  Once the tree is set to
      NULL, policy processing ceases.

      Each node in the valid_policy_tree includes four data objects: the
      valid policy, a set of associated policy qualifiers, a set of one
      or more expected policy values, and a criticality indicator.  If
      the node is at depth x, the components of the node have the
      following semantics:

         (1)  The valid_policy is a single policy OID representing a
         valid policy for the path of length x.

         (2)  The qualifier_set is a set of policy qualifiers associated
         with the valid policy in certificate x.

         (3)  The criticality_indicator indicates whether the
         certificate policy extension in certificate x was marked as
         critical.

         (4)  The expected_policy_set contains one or more policy OIDs
         that would satisfy this policy in the certificate x+1.

      The initial value of the valid_policy_tree is a single node with
      valid_policy anyPolicy, an empty qualifier_set, an
      expected_policy_set with the single value anyPolicy, and a
      criticality_indicator of FALSE.  This node is considered to be at
      depth zero.

      Figure 3 is a graphic representation of the initial state of the
      valid_policy_tree.  Additional figures will use this format to
      describe changes in the valid_policy_tree during path processing.

              +----------------+
              |   anyPolicy    |   <---- valid_policy
              +----------------+
              |       {}       |   <---- qualifier_set
              +----------------+
              |     FALSE      |   <---- criticality_indicator
              +----------------+
              |  {anyPolicy}   |   <---- expected_policy_set
              +----------------+

      Figure 3.  Initial value of the valid_policy_tree state variable

      (b) permitted_subtrees:  A set of root names for each name type
      (e.g., X.500 distinguished names, email addresses, or ip
      addresses) defining a set of subtrees within which all subject
      names in subsequent certificates in the certification path MUST
      fall.  This variable includes a set for each name type: the
      initial value for the set for Distinguished Names is the set of
      all Distinguished names; the initial value for the set of RFC822
      names is the set of all RFC822 names, etc.

      (c) excluded_subtrees:  A set of root names for each name type
      (e.g., X.500 distinguished names, email addresses, or ip
      addresses) defining a set of subtrees within which no subject name
      in subsequent certificates in the certification path may fall.
      This variable includes a set for each name type, and the initial
      value for each set is empty.

      (d) explicit_policy: an integer which indicates if a non-NULL
      valid_policy_tree is required. The integer indicates the number of
      non-self-issued certificates to be processed before this
      requirement is imposed.  Once set, this variable may be decreased,
      but may not be increased. That is, if a certificate in the path
      requires a non-NULL valid_policy_tree, a later certificate can not
      remove this requirement. If initial-explicit-policy is set, then
      the initial value is 0, otherwise the initial value is n+1.

      (e) inhibit_any-policy: an integer which indicates whether the
      anyPolicy policy identifier is considered a match. The integer
      indicates the number of non-self-issued certificates to be
      processed before the anyPolicy OID, if asserted in a certificate,
      is ignored. Once set, this variable may be decreased, but may not
      be increased. That is, if a certificate in the path inhibits
      processing of anyPolicy, a later certificate can not permit it.
      If initial-any-policy-inhibit is set, then the initial value is 0,
      otherwise the initial value is n+1.

      (f) policy_mapping: an integer which indicates if policy mapping
      is permitted.  The integer indicates the number of non-self-issued
      certificates to be processed before policy mapping is inhibited.
      Once set, this variable may be decreased, but may not be
      increased. That is, if a certificate in the path specifies policy
      mapping is not permitted, it can not be overridden by a later
      certificate. If initial-policy-mapping-inhibit is set, then the
      initial value is 0, otherwise the initial value is n+1.

      (g) working_public_key_algorithm: the digital signature algorithm
      used to verify the signature of a certificate.  The
      working_public_key_algorithm is initialized from the trusted
      public key algorithm provided in the trust anchor information.

      (h) working_public_key: the public key used to verify the
      signature of a certificate.  The working_public_key is initialized
      from the trusted public key provided in the trust anchor
      information.

      (i) working_public_key_parameters:  parameters associated with the
      current public key, that may be required to verify a signature
      (depending upon the algorithm).  The working_public_key_parameters
      variable is initialized from the trusted public key parameters
      provided in the trust anchor information.

      (j) working_issuer_name:  the issuer distinguished name expected
      in the next certificate in the chain.  The working_issuer_name is
      initialized to the trusted issuer provided in the trust anchor
      information.

      (k) max_path_length:  this integer is initialized to n, is
      decremented for each non-self-issued certificate in the path, and
      may be reduced to the value in the path length constraint field
      within the basic constraints extension of a CA certificate.

   Upon completion of the initialization steps, perform the basic
   certificate processing steps specified in 6.1.3.

6.1.3  Basic Certificate Processing

   The basic path processing actions to be performed for certificate i
   (for all i in [1..n]) are listed below.

      (a)  Verify the basic certificate information.  The certificate
      MUST satisfy each of the following:

         (1)  The certificate was signed with the
         working_public_key_algorithm using the working_public_key and
         the working_public_key_parameters.

         (2)  The certificate validity period includes the current time.

         (3)  At the current time, the certificate is not revoked and is
         not on hold status.  This may be determined by obtaining the
         appropriate CRL (section 6.3), status information, or by out-
         of-band mechanisms.

         (4)  The certificate issuer name is the working_issuer_name.

      (b)  If certificate i is self-issued and it is not the final
      certificate in the path, skip this step for certificate i.
      Otherwise, verify that the subject name is within one of the
      permitted_subtrees for X.500 distinguished names, and verify that
      each of the alternative names in the subjectAltName extension
      (critical or non-critical) is within one of the permitted_subtrees
      for that name type.

      (c)  If certificate i is self-issued and it is not the final
      certificate in the path, skip this step for certificate i.
      Otherwise, verify that the subject name is not within one of the
      excluded_subtrees for X.500 distinguished names, and verify that
      each of the alternative names in the subjectAltName extension
      (critical or non-critical) is not within one of the
      excluded_subtrees for that name type.

      (d)  If the certificate policies extension is present in the
      certificate and the valid_policy_tree is not NULL, process the
      policy information by performing the following steps in order:

         (1)  For each policy P not equal to anyPolicy in the
         certificate policies extension, let P-OID denote the OID in
         policy P and P-Q denote the qualifier set for policy P.
         Perform the following steps in order:

            (i)  If the valid_policy_tree includes a node of depth i-1
            where P-OID is in the expected_policy_set, create a child
            node as follows: set the valid_policy to OID-P; set the
            qualifier_set to P-Q, and set the expected_policy_set to
            {P-OID}.

            For example, consider a valid_policy_tree with a node of
            depth i-1 where the expected_policy_set is {Gold, White}.
            Assume the certificate policies Gold and Silver appear in
            the certificate policies extension of certificate i.  The
            Gold policy is matched but the Silver policy is not.  This
            rule will generate a child node of depth i for the Gold
            policy. The result is shown as Figure 4.

                             +-----------------+
                             |       Red       |
                             +-----------------+
                             |       {}        |
                             +-----------------+   node of depth i-1
                             |      FALSE      |
                             +-----------------+
                             |  {Gold, White}  |
                             +-----------------+
                                      |
                                      |
                                      |
                                      V
                             +-----------------+
                             |      Gold       |
                             +-----------------+
                             |       {}        |
                             +-----------------+ node of depth i
                             |  uninitialized  |
                             +-----------------+
                             |     {Gold}      |
                             +-----------------+

                    Figure 4.  Processing an exact match

            (ii)  If there was no match in step (i) and the
            valid_policy_tree includes a node of depth i-1 with the
            valid policy anyPolicy, generate a child node with the
            following values: set the valid_policy to P-OID; set the
            qualifier_set to P-Q, and set the expected_policy_set to
            {P-OID}.

            For example, consider a valid_policy_tree with a node of
            depth i-1 where the valid_policy is anyPolicy.  Assume the
            certificate policies Gold and Silver appear in the
            certificate policies extension of certificate i.  The Gold
            policy does not have a qualifier, but the Silver policy has
            the qualifier Q-Silver.  If Gold and Silver were not matched
            in (i) above, this rule will generate two child nodes of
            depth i, one for each policy.  The result is shown as Figure
            5.

                             +-----------------+
                             |    anyPolicy    |
                             +-----------------+
                             |       {}        |
                             +-----------------+ node of depth i-1
                             |      FALSE      |
                             +-----------------+
                             |   {anyPolicy}   |
                             +-----------------+
                                /           \
                               /             \
                              /               \
                             /                 \
               +-----------------+          +-----------------+
               |      Gold       |          |     Silver      |
               +-----------------+          +-----------------+
               |       {}        |          |   {Q-Silver}    |
               +-----------------+ nodes of +-----------------+
               | uninitialized   | depth i  | uninitialized   |
               +-----------------+          +-----------------+
               |     {Gold}      |          |    {Silver}     |
               +-----------------+          +-----------------+

               Figure 5.  Processing unmatched policies when a leaf node
               specifies anyPolicy

         (2)  If the certificate policies extension includes the policy
         anyPolicy with the qualifier set AP-Q and either (a)
         inhibit_any-policy is greater than 0 or (b) i<n and the
         certificate is self-issued, then:

         For each node in the valid_policy_tree of depth i-1, for each
         value in the expected_policy_set (including anyPolicy) that
         does not appear in a child node, create a child node with the
         following values: set the valid_policy to the value from the
         expected_policy_set in the parent node; set the qualifier_set
         to AP-Q, and set the expected_policy_set to the value in the
         valid_policy from this node.

         For example, consider a valid_policy_tree with a node of depth
         i-1 where the expected_policy_set is {Gold, Silver}.  Assume
         anyPolicy appears in the certificate policies extension of
         certificate i, but Gold and Silver do not.  This rule will
         generate two child nodes of depth i, one for each policy.  The
         result is shown below as Figure 6.

                          +-----------------+
                          |      Red        |
                          +-----------------+
                          |       {}        |
                          +-----------------+ node of depth i-1
                          |      FALSE      |
                          +-----------------+
                          |  {Gold, Silver} |
                          +-----------------+
                             /           \
                            /             \
                           /               \
                          /                 \
            +-----------------+          +-----------------+
            |      Gold       |          |     Silver      |
            +-----------------+          +-----------------+
            |       {}        |          |       {}        |
            +-----------------+ nodes of +-----------------+
            |  uninitialized  | depth i  |  uninitialized  |
            +-----------------+          +-----------------+
            |     {Gold}      |          |    {Silver}     |
            +-----------------+          +-----------------+

         Figure 6.  Processing unmatched policies when the certificate
         policies extension specifies anyPolicy

         (3)  If there is a node in the valid_policy_tree of depth i-1
         or less without any child nodes, delete that node.  Repeat this
         step until there are no nodes of depth i-1 or less without
         children.

         For example, consider the valid_policy_tree shown in Figure 7
         below.  The two nodes at depth i-1 that are marked with an 'X'
         have no children, and are deleted.  Applying this rule to the
         resulting tree will cause the node at depth i-2 that is marked
         with an 'Y' to be deleted.  The following application of the
         rule does not cause any nodes to be deleted, and this step is
         complete.

                              +-----------+
                              |           | node of depth i-3
                              +-----------+
                              /     |     \
                             /      |      \
                            /       |       \
                +-----------+ +-----------+ +-----------+
                |           | |           | |     Y     | nodes of
                +-----------+ +-----------+ +-----------+ depth i-2
                /   \               |             |
               /     \              |             |
              /       \             |             |
   +-----------+ +-----------+ +-----------+ +-----------+ nodes of
   |           | |     X     | |           | |    X      |  depth
   +-----------+ +-----------+ +-----------+ +-----------+   i-1
         |                      /    |    \
         |                     /     |     \
         |                    /      |      \
   +-----------+ +-----------+ +-----------+ +-----------+ nodes of
   |           | |           | |           | |           |  depth
   +-----------+ +-----------+ +-----------+ +-----------+   i

          Figure 7.  Pruning the valid_policy_tree

         (4)  If the certificate policies extension was marked as
         critical, set the criticality_indicator in all nodes of depth i
         to TRUE.  If the certificate policies extension was not marked
         critical, set the criticality_indicator in all nodes of depth i
         to FALSE.

      (e)  If the certificate policies extension is not present, set the
      valid_policy_tree to NULL.

      (f)  Verify that either explicit_policy is greater than 0 or the
      valid_policy_tree is not equal to NULL;

   If any of steps (a), (b), (c), or (f) fails, the procedure
   terminates, returning a failure indication and an appropriate reason.

   If i is not equal to n, continue by performing the preparatory steps
   listed in 6.1.4.  If i is equal to n, perform the wrap-up steps
   listed in 6.1.5.

6.1.4  Preparation for Certificate i+1

   To prepare for processing of certificate i+1, perform the following
   steps for certificate i:

      (a)  If a policy mapping extension is present, verify that the
      special value anyPolicy does not appear as an issuerDomainPolicy
      or a subjectDomainPolicy.

      (b)  If a policy mapping extension is present, then for each
      issuerDomainPolicy ID-P in the policy mapping extension:

         (1)  If the policy_mapping variable is greater than 0, for each
         node in the valid_policy_tree of depth i where ID-P is the
         valid_policy, set expected_policy_set to the set of
         subjectDomainPolicy values that are specified as equivalent to
         ID-P by the policy mapping extension.

         If no node of depth i in the valid_policy_tree has a
         valid_policy of ID-P but there is a node of depth i with a
         valid_policy of anyPolicy, then generate a child node of the
         node of depth i-1 that has a valid_policy of anyPolicy as
         follows:

            (i)  set the valid_policy to ID-P;

            (ii)  set the qualifier_set to the qualifier set of the
            policy anyPolicy in the certificate policies extension of
            certificate i;

            (iii)  set the criticality_indicator to the criticality of
            the certificate policies extension of certificate i;

            (iv)  and set the expected_policy_set to the set of
            subjectDomainPolicy values that are specified as equivalent
            to ID-P by the policy mappings extension.

         (2)  If the policy_mapping variable is equal to 0:

            (i)  delete each node of depth i in the valid_policy_tree
            where ID-P is the valid_policy.

            (ii)  If there is a node in the valid_policy_tree of depth
            i-1 or less without any child nodes, delete that node.
            Repeat this step until there are no nodes of depth i-1 or
            less without children.

      (c)  Assign the certificate subject name to working_issuer_name.

      (d)  Assign the certificate subjectPublicKey to
      working_public_key.

      (e)  If the subjectPublicKeyInfo field of the certificate contains
      an algorithm field with non-null parameters, assign the parameters
      to the working_public_key_parameters variable.

      If the subjectPublicKeyInfo field of the certificate contains an
      algorithm field with null parameters or parameters are omitted,
      compare the certificate subjectPublicKey algorithm to the
      working_public_key_algorithm.  If the certificate subjectPublicKey
      algorithm and the working_public_key_algorithm are different, set
      the working_public_key_parameters to null.

      (f)  Assign the certificate subjectPublicKey algorithm to the
      working_public_key_algorithm variable.

      (g)  If a name constraints extension is included in the
      certificate, modify the permitted_subtrees and excluded_subtrees
      state variables as follows:

         (1)  If permittedSubtrees is present in the certificate, set
         the permitted_subtrees state variable to the intersection of
         its previous value and the value indicated in the extension
         field.  If permittedSubtrees does not include a particular name
         type, the permitted_subtrees state variable is unchanged for
         that name type.  For example, the intersection of nist.gov and
         csrc.nist.gov is csrc.nist.gov.  And, the intersection of
         nist.gov and rsasecurity.com is the empty set.

         (2)  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.  If
         excludedSubtrees does not include a particular name type, the
         excluded_subtrees state variable is unchanged for that name
         type.  For example, the union of the name spaces nist.gov and
         csrc.nist.gov is nist.gov.  And, the union of nist.gov and
         rsasecurity.com is both name spaces.

      (h)  If the issuer and subject names are not identical:

         (1)  If explicit_policy is not 0, decrement explicit_policy by
         1.

         (2)  If policy_mapping is not 0, decrement policy_mapping by 1.

         (3)  If inhibit_any-policy is not 0, decrement inhibit_any-
         policy by 1.

      (i)  If a policy constraints extension is included in the
      certificate, modify the explicit_policy and policy_mapping state
      variables as follows:

         (1)  If requireExplicitPolicy is present and is less than
         explicit_policy, set explicit_policy to the value of
         requireExplicitPolicy.

         (2)  If inhibitPolicyMapping is present and is less than
         policy_mapping, set policy_mapping to the value of
         inhibitPolicyMapping.

      (j)  If the inhibitAnyPolicy extension is included in the
      certificate and is less than inhibit_any-policy, set inhibit_any-
      policy to the value of inhibitAnyPolicy.

      (k)  Verify that the certificate is a CA certificate (as specified
      in a basicConstraints extension or as verified out-of-band).

      (l)  If the certificate was not self-issued, verify that
      max_path_length is greater than zero and decrement max_path_length
      by 1.

      (m)  If pathLengthConstraint is present in the certificate and is
      less than max_path_length, set max_path_length to the value of
      pathLengthConstraint.

      (n)  If a key usage extension is present, verify that the
      keyCertSign bit is set.

      (o)  Recognize and process any other critical extension present in
      the certificate.  Process any other recognized non-critical
      extension present in the certificate.

   If check (a), (k), (l), (n) or (o) fails, the procedure terminates,
   returning a failure indication and an appropriate reason.

   If (a), (k), (l), (n) and (o) have completed successfully, increment
   i and perform the basic certificate processing specified in 6.1.3.

6.1.5  Wrap-up procedure

   To complete the processing of the end entity certificate, perform the
   following steps for certificate n:

      (a)  If certificate n was not self-issued and explicit_policy is
      not 0, decrement explicit_policy by 1.

      (b)  If a policy constraints extension is included in the
      certificate and requireExplicitPolicy is present and has a value
      of 0, set the explicit_policy state variable to 0.

      (c)  Assign the certificate subjectPublicKey to
      working_public_key.

      (d)  If the subjectPublicKeyInfo field of the certificate contains
      an algorithm field with non-null parameters, assign the parameters
      to the working_public_key_parameters variable.

      If the subjectPublicKeyInfo field of the certificate contains an
      algorithm field with null parameters or parameters are omitted,
      compare the certificate subjectPublicKey algorithm to the
      working_public_key_algorithm.  If the certificate subjectPublicKey
      algorithm and the working_public_key_algorithm are different, set
      the working_public_key_parameters to null.

      (e)  Assign the certificate subjectPublicKey algorithm to the
      working_public_key_algorithm variable.

      (f)  Recognize and process any other critical extension present in
      the certificate n.  Process any other recognized non-critical
      extension present in certificate n.

      (g)  Calculate the intersection of the valid_policy_tree and the
      user-initial-policy-set, as follows:

         (i)  If the valid_policy_tree is NULL, the intersection is
         NULL.

         (ii)  If the valid_policy_tree is not NULL and the user-
         initial-policy-set is any-policy, the intersection is the
         entire valid_policy_tree.

         (iii)  If the valid_policy_tree is not NULL and the user-
         initial-policy-set is not any-policy, calculate the
         intersection of the valid_policy_tree and the user-initial-
         policy-set as follows:

            1.  Determine the set of policy nodes whose parent nodes
            have a valid_policy of anyPolicy.  This is the
            valid_policy_node_set.

            2.  If the valid_policy of any node in the
            valid_policy_node_set is not in the user-initial-policy-set
            and is not anyPolicy, delete this node and all its children.

            3.  If the valid_policy_tree includes a node of depth n with
            the valid_policy anyPolicy and the user-initial-policy-set
            is not any-policy perform the following steps:

               a. Set P-Q to the qualifier_set in the node of depth n
               with valid_policy anyPolicy.

               b. For each P-OID in the user-initial-policy-set that is
               not the valid_policy of a node in the
               valid_policy_node_set, create a child node whose parent
               is the node of depth n-1 with the valid_policy anyPolicy.
               Set the values in the child node as follows: set the
               valid_policy to P-OID; set the qualifier_set to P-Q; copy
               the criticality_indicator from the node of depth n with
               the valid_policy anyPolicy; and set the
               expected_policy_set to {P-OID}.

               c.  Delete the node of depth n with the valid_policy
               anyPolicy.

            4.  If there is a node in the valid_policy_tree of depth n-1
            or less without any child nodes, delete that node.  Repeat
            this step until there are no nodes of depth n-1 or less
            without children.

   If either (1) the value of explicit_policy variable is greater than
   zero, or (2) the valid_policy_tree is not NULL, then path processing
   has succeeded.

6.1.6  Outputs

   If path processing succeeds, the procedure terminates, returning a
   success indication together with final value of the
   valid_policy_tree, the working_public_key, the
   working_public_key_algorithm, and the working_public_key_parameters.

6.2  Using the Path Validation Algorithm

   The path validation algorithm describes the process of validating a
   single certification path.  While each certification path begins with
   a specific trust anchor, there is no requirement that all
   certification paths validated by a particular system share a single
   trust anchor.  An implementation that supports multiple trust anchors
   MAY augment the algorithm presented in section 6.1 to further limit
   the set of valid certification paths which begin with a particular
   trust anchor.  For example, an implementation MAY modify the
   algorithm to apply name constraints to a specific trust anchor during
   the initialization phase, or the application MAY require the presence

   of a particular alternative name form in the end entity certificate,
   or the application MAY impose requirements on application-specific
   extensions.  Thus, the path validation algorithm presented in section
   6.1 defines the minimum conditions for a path to be considered valid.

   The selection of one or more trusted CAs is a local decision.  A
   system may provide any one of its trusted CAs as the trust anchor for
   a particular path.  The inputs to the path validation algorithm may
   be different for each path.  The inputs used to process a path may
   reflect application-specific requirements or limitations in the trust
   accorded a particular trust anchor.  For example, a trusted CA may
   only be trusted for a particular certificate policy.  This
   restriction can be expressed through the inputs to the path
   validation procedure.

   It is also possible to specify an extended version of the above
   certification path processing procedure which results in default
   behavior identical to the rules of PEM [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.

6.3  CRL Validation

   This section describes the steps necessary to determine if a
   certificate is revoked or on hold status when CRLs are the revocation
   mechanism used by the certificate issuer.  Conforming implementations
   that support CRLs are not required to implement this algorithm, but
   they MUST be functionally equivalent to the external behavior
   resulting from this procedure.  Any algorithm may be used by a
   particular implementation so long as it derives the correct result.

   This algorithm assumes that all of the needed CRLs are available in a
   local cache.  Further, if the next update time of a CRL has passed,
   the algorithm assumes a mechanism to fetch a current CRL and place it
   in the local CRL cache.

   This algorithm defines a set of inputs, a set of state variables, and
   processing steps that are performed for each certificate in the path.
   The algorithm output is the revocation status of the certificate.

6.3.1  Revocation Inputs

   To support revocation processing, the algorithm requires two inputs:

      (a)  certificate:  The algorithm requires the certificate serial
      number and issuer name to determine whether a certificate is on a
      particular CRL.  The basicConstraints extension is used to
      determine whether the supplied certificate is associated with a CA
      or an end entity.  If present, the algorithm uses the
      cRLDistributionsPoint and freshestCRL extensions to determine
      revocation status.

      (b)  use-deltas:  This boolean input determines whether delta CRLs
      are applied to CRLs.

      Note that implementations supporting legacy PKIs, such as RFC 1422
      and X.509 version 1, will need an additional input indicating
      whether the supplied certificate is associated with a CA or an end
      entity.

6.3.2  Initialization and Revocation State Variables

   To support CRL processing, the algorithm requires the following state
   variables:

      (a)  reasons_mask:  This variable contains the set of revocation
      reasons supported by the CRLs and delta CRLs processed so far.
      The legal members of the set are the possible revocation reason
      values: unspecified, keyCompromise, caCompromise,
      affiliationChanged, superseded, cessationOfOperation,
      certificateHold, privilegeWithdrawn, and aACompromise.  The
      special value all-reasons is used to denote the set of all legal
      members.  This variable is initialized to the empty set.

      (b)  cert_status:  This variable contains the status of the
      certificate.  This variable may be assigned one of the following
      values: unspecified, keyCompromise, caCompromise,
      affiliationChanged, superseded, cessationOfOperation,
      certificateHold, removeFromCRL, privilegeWithdrawn, aACompromise,
      the special value UNREVOKED, or the special value UNDETERMINED.
      This variable is initialized to the special value UNREVOKED.

      (c)  interim_reasons_mask:  This contains the set of revocation
      reasons supported by the CRL or delta CRL currently being
      processed.

   Note: In some environments, it is not necessary to check all reason
   codes.  For example, some environments are only concerned with
   caCompromise and keyCompromise for CA certificates.  This algorithm
   checks all reason codes.  Additional processing and state variables
   may be necessary to limit the checking to a subset of the reason
   codes.

6.3.3  CRL Processing

   This algorithm begins by assuming the certificate is not revoked.
   The algorithm checks one or more CRLs until either the certificate
   status is determined to be revoked or sufficient CRLs have been
   checked to cover all reason codes.

   For each distribution point (DP) in the certificate CRL distribution
   points extension, for each corresponding CRL in the local CRL cache,
   while ((reasons_mask is not all-reasons) and (cert_status is
   UNREVOKED)) perform the following:

      (a)  Update the local CRL cache by obtaining a complete CRL, a
      delta CRL, or both, as required:

         (1)  If the current time is after the value of the CRL next
         update field, then do one of the following:

            (i)  If use-deltas is set and either the certificate or the
            CRL contains the freshest CRL extension, obtain a delta CRL
            with the a next update value that is after the current time
            and can be used to update the locally cached CRL as
            specified in section 5.2.4.

            (ii)  Update the local CRL cache with a current complete
            CRL, verify that the current time is before the next update
            value in the new CRL, and continue processing with the new
            CRL.  If use-deltas is set, then obtain the current delta
            CRL that can be used to update the new locally cached
            complete CRL as specified in section 5.2.4.

         (2)  If the current time is before the value of the next update
         field and use-deltas is set, then obtain the current delta CRL
         that can be used to update the locally cached complete CRL as
         specified in section 5.2.4.

      (b)  Verify the issuer and scope of the complete CRL as follows:

         (1)  If the DP includes cRLIssuer, then verify that the issuer
         field in the complete CRL matches cRLIssuer in the DP and that
         the complete CRL contains an issuing distribution point
         extension with the indrectCRL boolean asserted.  Otherwise,
         verify that the CRL issuer matches the certificate issuer.

         (2)  If the complete CRL includes an issuing distribution point
         (IDP) CRL extension check the following:

            (i)  If the distribution point name is present in the IDP
            CRL extension and the distribution field is present in the
            DP, then verify that one of the names in the IDP matches one
            of the names in the DP.  If the distribution point name is
            present in the IDP CRL extension and the distribution field
            is omitted from the DP, then verify that one of the names in
            the IDP matches one of the names in the cRLIssuer field of
            the DP.

            (ii)  If the onlyContainsUserCerts boolean is asserted in
            the IDP CRL extension, verify that the certificate does not
            include the basic constraints extension with the cA boolean
            asserted.

            (iii)  If the onlyContainsCACerts boolean is asserted in the
            IDP CRL extension, verify that the certificate includes the
            basic constraints extension with the cA boolean asserted.

            (iv)  Verify that the onlyContainsAttributeCerts boolean is
            not asserted.

      (c)  If use-deltas is set, verify the issuer and scope of the
      delta CRL as follows:

         (1)  Verify that the delta CRL issuer matches complete CRL
         issuer.

         (2)  If the complete CRL includes an issuing distribution point
         (IDP) CRL extension, verify that the delta CRL contains a
         matching IDP CRL extension.  If the complete CRL omits an IDP
         CRL extension, verify that the delta CRL also omits an IDP CRL
         extension.

         (3)  Verify that the delta CRL authority key identifier
         extension matches complete CRL authority key identifier
         extension.

   (d)  Compute the interim_reasons_mask for this CRL as follows:

         (1)  If the issuing distribution point (IDP) CRL extension is
         present and includes onlySomeReasons and the DP includes
         reasons, then set interim_reasons_mask to the intersection of
         reasons in the DP and onlySomeReasons in IDP CRL extension.

         (2)  If the IDP CRL extension includes onlySomeReasons but the
         DP omits reasons, then set interim_reasons_mask to the value of
         onlySomeReasons in IDP CRL extension.

         (3)  If the IDP CRL extension is not present or omits
         onlySomeReasons but the DP includes reasons, then set
         interim_reasons_mask to the value of DP reasons.

         (4)  If the IDP CRL extension is not present or omits
         onlySomeReasons and the DP omits reasons, then set
         interim_reasons_mask to the special value all-reasons.

   (e)  Verify that interim_reasons_mask includes one or more reasons
   that is not included in the reasons_mask.

   (f)  Obtain and validate the certification path for the complete CRL
   issuer.  If a key usage extension is present in the CRL issuer's
   certificate, verify that the cRLSign bit is set.

   (g)  Validate the signature on the complete CRL using the public key
   validated in step (f).

   (h)  If use-deltas is set, then validate the signature on the delta
   CRL using the public key validated in step (f).

   (i)  If use-deltas is set, then search for the certificate on the
   delta CRL.  If an entry is found that matches the certificate issuer
   and serial number as described in section 5.3.4, then set the
   cert_status variable to the indicated reason as follows:

         (1)  If the reason code CRL entry extension is present, set the
         cert_status variable to the value of the reason code CRL entry
         extension.

         (2)  If the reason code CRL entry extension is not present, set
         the cert_status variable to the value unspecified.

      (j)  If (cert_status is UNREVOKED), then search for the
      certificate on the complete CRL.  If an entry is found that
      matches the certificate issuer and serial number as described in
      section 5.3.4, then set the cert_status variable to the indicated
      reason as described in step (i).

      (k)  If (cert_status is removeFromCRL), then set cert_status to
      UNREVOKED.

   If ((reasons_mask is all-reasons) OR (cert_status is not UNREVOKED)),
   then the revocation status has been determined, so return
   cert_status.

   If the revocation status has not been determined, repeat the process
   above with any available CRLs not specified in a distribution point
   but issued by the certificate issuer.  For the processing of such a
   CRL, assume a DP with both the reasons and the cRLIssuer fields
   omitted and a distribution point name of the certificate issuer.
   That is, the sequence of names in fullName is generated from the
   certificate issuer field as well as the certificate issuerAltName
   extension.  If the revocation status remains undetermined, then
   return the cert_status UNDETERMINED.

7  References

   [ISO 10646] ISO/IEC 10646-1:1993.  International Standard --
               Information technology -- Universal Multiple-Octet Coded
               Character Set (UCS) -- Part 1: Architecture and Basic
               Multilingual Plane.

   [RFC 791]   Postel, J.,  "Internet Protocol", STD 5, RFC 791,
               September 1981.

   [RFC 822]   Crocker, D., "Standard for the format of ARPA Internet
               text messages", STD 11, RFC 822, August 1982.

   [RFC 1034]  Mockapetris, P., "Domain Names - Concepts and
               Facilities", STD 13, RFC 1034, November 1987.

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

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

   [RFC 1510]  Kohl, J. and C. Neuman, "The Kerberos Network
               Authentication Service (V5)," RFC 1510, September 1993.

   [RFC 1519]  Fuller, V., T. Li, J. Yu and K. Varadhan, "Classless
               Inter-Domain Routing (CIDR): An Address Assignment and
               Aggregation Strategy", RFC 1519, September 1993.

   [RFC 1738]  Berners-Lee, T., L. Masinter and M. McCahill, "Uniform
               Resource Locators (URL)", RFC 1738, December 1994.

   [RFC 1778]  Howes, T., S. Kille, W. Yeong and C. Robbins, "The String
               Representation of Standard Attribute Syntaxes," RFC 1778,
               March 1995.

   [RFC 1883]  Deering, S. and R. Hinden.  "Internet Protocol, Version 6
               (IPv6) Specification", RFC 1883, December 1995.

   [RFC 2044]  F. Yergeau, F., "UTF-8, a transformation format of
               Unicode and ISO 10646", RFC 2044, October 1996.

   [RFC 2119]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC 2247]  Kille, S., M. Wahl, A. Grimstad, R. Huber and S.
               Sataluri, "Using Domains in LDAP/X.500 Distinguished
               Names", RFC 2247, January 1998.

   [RFC 2252]  Wahl, M., A. Coulbeck, T. Howes and S. Kille,
               "Lightweight Directory Access Protocol (v3):  Attribute
               Syntax Definitions", RFC 2252, December 1997.

   [RFC 2277]  Alvestrand, H., "IETF Policy on Character Sets and
               Languages", BCP 18, RFC 2277, January 1998.

   [RFC 2279]  Yergeau, F., "UTF-8, a transformation format of ISO
               10646", RFC 2279, January 1998.

   [RFC 2459]  Housley, R., W. Ford, W. Polk and D. Solo, "Internet
               X.509 Public Key Infrastructure: Certificate and CRL
               Profile", RFC 2459, January 1999.

   [RFC 2560]  Myers, M., R. Ankney, A. Malpani, S. Galperin and C.
               Adams, "Online Certificate Status Protocal - OCSP", June
               1999.

   [SDN.701]   SDN.701, "Message Security Protocol 4.0", Revision A,
               1997-02-06.

   [X.501]     ITU-T Recommendation X.501: Information Technology - Open
               Systems Interconnection - The Directory: Models, 1993.

   [X.509]     ITU-T Recommendation X.509 (1997 E): Information
               Technology - Open Systems Interconnection - The
               Directory: Authentication Framework, June 1997.

   [X.520]     ITU-T Recommendation X.520: Information Technology - Open
               Systems Interconnection - The Directory: Selected
               Attribute Types, 1993.

   [X.660]     ITU-T Recommendation X.660 Information Technology - ASN.1
               encoding rules: Specification of Basic Encoding Rules
               (BER), Canonical Encoding Rules (CER) and Distinguished
               Encoding Rules (DER), 1997.

   [X.690]     ITU-T Recommendation X.690 Information Technology - Open
               Systems Interconnection - Procedures for the operation of
               OSI Registration Authorities: General procedures, 1992.

   [X9.55]     ANSI X9.55-1995, Public Key Cryptography For The
               Financial Services Industry: Extensions To Public Key
               Certificates And Certificate Revocation Lists, 8
               December, 1995.

   [PKIXALGS]  Bassham, L., Polk, W. and R. Housley, "Algorithms and
               Identifiers for the Internet X.509 Public Key
               Infrastructure Certificate and Certificate Revocation
               Lists (CRL) Profile", RFC 3279, April 2002.

   [PKIXTSA]   Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
               "Internet X.509 Public Key Infrastructure Time-Stamp
               Protocol (TSP)", RFC 3161, August 2001.

8  Intellectual Property Rights

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights (see http://www.ietf.org/ipr.html).

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and

   standards-related documentation can be found in BCP 11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

9  Security Considerations

   The majority of this specification is devoted to the format and
   content of certificates and CRLs.  Since certificates and CRLs are
   digitally signed, no additional integrity service is necessary.
   Neither certificates nor CRLs need be kept secret, and unrestricted
   and anonymous access to certificates and CRLs has no security
   implications.

   However, security factors outside the scope of this specification
   will affect the assurance provided to certificate users.  This
   section highlights critical issues to be considered by implementers,
   administrators, and users.

   The procedures performed by CAs and RAs to validate the binding of
   the subject's identity to their public key greatly affect the
   assurance that ought to be placed in the certificate.  Relying
   parties might wish to review the CA's certificate practice statement.
   This is particularly important when issuing certificates to other
   CAs.

   The use of a single key pair for both signature and other purposes is
   strongly discouraged.  Use of separate key pairs for signature and
   key management provides several benefits to the users.  The
   ramifications associated with loss or disclosure of a signature key
   are different from loss or disclosure of a key management key.  Using
   separate key pairs permits a balanced and flexible response.
   Similarly, different validity periods or key lengths for each key
   pair may be appropriate in some application environments.
   Unfortunately, some legacy applications (e.g., SSL) use a single key
   pair for signature and key management.

   The protection afforded private keys is a critical security factor.
   On a small scale, failure of users to protect their private keys will
   permit an attacker to masquerade as them, or decrypt their personal
   information.  On a larger scale, compromise of a CA's private signing
   key may have a catastrophic effect.  If an attacker obtains the
   private key unnoticed, the attacker may issue bogus certificates and
   CRLs.  Existence of bogus certificates and CRLs will undermine
   confidence in the system.  If such a compromise is detected, all
   certificates issued to the compromised CA MUST be revoked, preventing

   services between its users and users of other CAs.  Rebuilding after
   such a compromise will be problematic, so CAs are advised to
   implement a combination of strong technical measures (e.g., tamper-
   resistant cryptographic modules) and appropriate management
   procedures (e.g., separation of duties) to avoid such an incident.

   Loss of a CA's private signing key may also be problematic.  The CA
   would not be able to produce CRLs or perform normal key rollover.
   CAs SHOULD maintain secure backup for signing keys.  The security of
   the key backup procedures is a critical factor in avoiding key
   compromise.

   The availability and freshness of revocation information affects the
   degree of assurance that ought to be placed in a certificate.  While
   certificates expire naturally, events may occur during its natural
   lifetime which negate the binding between the subject and public key.
   If revocation information is untimely or unavailable, the assurance
   associated with the binding is clearly reduced.  Relying parties
   might not be able to process every critical extension that can appear
   in a CRL.  CAs SHOULD take extra care when making revocation
   information available only through CRLs that contain critical
   extensions, particularly if support for those extensions is not
   mandated by this profile.  For example, if revocation information is
   supplied using a combination of delta CRLs and full CRLs, and the
   delta CRLs are issued more frequently than the full CRLs, then
   relying parties that cannot handle the critical extensions related to
   delta CRL processing will not be able to obtain the most recent
   revocation information.  Alternatively, if a full CRL is issued
   whenever a delta CRL is issued, then timely revocation information
   will be available to all relying parties.  Similarly, implementations
   of the certification path validation mechanism described in section 6
   that omit revocation checking provide less assurance than those that
   support it.

   The certification path validation algorithm depends on the certain
   knowledge of the public keys (and other information) about one or
   more trusted CAs.  The decision to trust a CA is an important
   decision as it ultimately determines the trust afforded a
   certificate.  The authenticated distribution of trusted CA public
   keys (usually in the form of a "self-signed" certificate) is a
   security critical out-of-band process that is beyond the scope of
   this specification.

   In addition, where a key compromise or CA failure occurs for a
   trusted CA, the user will need to modify the information provided to
   the path validation routine.  Selection of too many trusted CAs makes

   the trusted CA information difficult to maintain.  On the other hand,
   selection of only one trusted CA could limit users to a closed
   community of users.

   The quality of implementations that process certificates also affects
   the degree of assurance provided.  The path validation algorithm
   described in section 6 relies upon the integrity of the trusted CA
   information, and especially the integrity of the public keys
   associated with the trusted CAs.  By substituting public keys for
   which an attacker has the private key, an attacker could trick the
   user into accepting false certificates.

   The binding between a key and certificate subject cannot be stronger
   than the cryptographic module implementation and algorithms used to
   generate the signature.  Short key lengths or weak hash algorithms
   will limit the utility of a certificate.  CAs are encouraged to note
   advances in cryptology so they can employ strong cryptographic
   techniques.  In addition, CAs SHOULD decline to issue certificates to
   CAs or end entities that generate weak signatures.

   Inconsistent application of name comparison rules can result in
   acceptance of invalid X.509 certification paths, or rejection of
   valid ones.  The X.500 series of specifications defines rules for
   comparing distinguished names that require comparison of strings
   without regard to case, character set, multi-character white space
   substring, or leading and trailing white space.  This specification
   relaxes these requirements, requiring support for binary comparison
   at a minimum.

   CAs MUST encode the distinguished name in the subject field of a CA
   certificate identically to the distinguished name in the issuer field
   in certificates issued by that CA.  If CAs use different encodings,
   implementations might fail to recognize name chains for paths that
   include this certificate.  As a consequence, valid paths could be
   rejected.

   In addition, name constraints for distinguished names MUST be stated
   identically to the encoding used in the subject field or
   subjectAltName extension.  If not, then name constraints stated as
   excludedSubTrees will not match and invalid paths will be accepted
   and name constraints expressed as permittedSubtrees will not match
   and valid paths will be rejected.  To avoid acceptance of invalid
   paths, CAs SHOULD state name constraints for distinguished names as
   permittedSubtrees wherever possible.

Appendix A.  Psuedo-ASN.1 Structures and OIDs

   This section describes data objects used by conforming PKI components
   in an "ASN.1-like" syntax.  This syntax is a hybrid of the 1988 and
   1993 ASN.1 syntaxes.  The 1988 ASN.1 syntax is augmented with 1993
   UNIVERSAL Types UniversalString, BMPString and UTF8String.

   The ASN.1 syntax does not permit the inclusion of type statements in
   the ASN.1 module, and the 1993 ASN.1 standard does not permit use of
   the new UNIVERSAL types in modules using the 1988 syntax.  As a
   result, this module does not conform to either version of the ASN.1
   standard.

   This appendix may be converted into 1988 ASN.1 by replacing the
   definitions for the UNIVERSAL Types with the 1988 catch-all "ANY".

A.1 Explicitly Tagged Module, 1988 Syntax

PKIX1Explicit88 { iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) }

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

-- IMPORTS NONE --

-- UNIVERSAL Types defined in 1993 and 1998 ASN.1
-- and required by this specification

UniversalString ::= [UNIVERSAL 28] IMPLICIT OCTET STRING
        -- UniversalString is defined in ASN.1:1993

BMPString ::= [UNIVERSAL 30] IMPLICIT OCTET STRING
      -- BMPString is the subtype of UniversalString and models
      -- the Basic Multilingual Plane of ISO/IEC/ITU 10646-1

UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
      -- The content of this type conforms to RFC 2279.

-- PKIX specific OIDs

id-pkix  OBJECT IDENTIFIER  ::=
         { iso(1) identified-organization(3) dod(6) internet(1)
                    security(5) mechanisms(5) pkix(7) }

-- PKIX arcs

id-pe OBJECT IDENTIFIER  ::=  { id-pkix 1 }
        -- arc for private certificate extensions
id-qt OBJECT IDENTIFIER ::= { id-pkix 2 }
        -- arc for policy qualifier types
id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
        -- arc for extended key purpose OIDS
id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
        -- arc for access descriptors

-- policyQualifierIds for Internet policy qualifiers

id-qt-cps      OBJECT IDENTIFIER ::=  { id-qt 1 }
      -- OID for CPS qualifier
id-qt-unotice  OBJECT IDENTIFIER ::=  { id-qt 2 }
      -- OID for user notice qualifier

-- access descriptor definitions

id-ad-ocsp         OBJECT IDENTIFIER ::= { id-ad 1 }
id-ad-caIssuers    OBJECT IDENTIFIER ::= { id-ad 2 }
id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }
id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

-- attribute data types

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

AttributeType           ::=  OBJECT IDENTIFIER

AttributeValue          ::=  ANY

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

-- suggested naming attributes: Definition of the following
--   information object set may be augmented to meet local
--   requirements.  Note that deleting members of the set may
--   prevent interoperability with conforming implementations.
-- presented in pairs: the AttributeType followed by the
--   type definition for the corresponding AttributeValue
--Arc for standard naming attributes
id-at OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 4 }

-- Naming attributes of type X520name

id-at-name              AttributeType ::= { id-at 41 }
id-at-surname           AttributeType ::= { id-at 4 }
id-at-givenName         AttributeType ::= { id-at 42 }
id-at-initials          AttributeType ::= { id-at 43 }
id-at-generationQualifier AttributeType ::= { id-at 44 }

X520name ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-name)),
      printableString   PrintableString (SIZE (1..ub-name)),
      universalString   UniversalString (SIZE (1..ub-name)),
      utf8String        UTF8String      (SIZE (1..ub-name)),
      bmpString         BMPString       (SIZE (1..ub-name)) }

-- Naming attributes of type X520CommonName

id-at-commonName        AttributeType ::= { id-at 3 }

X520CommonName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-common-name)),
      printableString   PrintableString (SIZE (1..ub-common-name)),
      universalString   UniversalString (SIZE (1..ub-common-name)),
      utf8String        UTF8String      (SIZE (1..ub-common-name)),
      bmpString         BMPString       (SIZE (1..ub-common-name)) }

-- Naming attributes of type X520LocalityName

id-at-localityName      AttributeType ::= { id-at 7 }

X520LocalityName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-locality-name)),
      printableString   PrintableString (SIZE (1..ub-locality-name)),
      universalString   UniversalString (SIZE (1..ub-locality-name)),
      utf8String        UTF8String      (SIZE (1..ub-locality-name)),
      bmpString         BMPString       (SIZE (1..ub-locality-name)) }

-- Naming attributes of type X520StateOrProvinceName

id-at-stateOrProvinceName AttributeType ::= { id-at 8 }

X520StateOrProvinceName ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-state-name)),
      printableString   PrintableString (SIZE (1..ub-state-name)),
      universalString   UniversalString (SIZE (1..ub-state-name)),
      utf8String        UTF8String      (SIZE (1..ub-state-name)),
      bmpString         BMPString       (SIZE(1..ub-state-name)) }

-- Naming attributes of type X520OrganizationName

id-at-organizationName  AttributeType ::= { id-at 10 }

X520OrganizationName ::= CHOICE {
      teletexString     TeletexString
                          (SIZE (1..ub-organization-name)),
      printableString   PrintableString
                          (SIZE (1..ub-organization-name)),
      universalString   UniversalString
                          (SIZE (1..ub-organization-name)),
      utf8String        UTF8String
                          (SIZE (1..ub-organization-name)),
      bmpString         BMPString
                          (SIZE (1..ub-organization-name))  }

-- Naming attributes of type X520OrganizationalUnitName

id-at-organizationalUnitName AttributeType ::= { id-at 11 }

X520OrganizationalUnitName ::= CHOICE {
      teletexString     TeletexString
                          (SIZE (1..ub-organizational-unit-name)),
      printableString   PrintableString
                          (SIZE (1..ub-organizational-unit-name)),
      universalString   UniversalString
                          (SIZE (1..ub-organizational-unit-name)),
      utf8String        UTF8String
                          (SIZE (1..ub-organizational-unit-name)),
      bmpString         BMPString
                          (SIZE (1..ub-organizational-unit-name)) }

-- Naming attributes of type X520Title

id-at-title             AttributeType ::= { id-at 12 }

X520Title ::= CHOICE {
      teletexString     TeletexString   (SIZE (1..ub-title)),
      printableString   PrintableString (SIZE (1..ub-title)),
      universalString   UniversalString (SIZE (1..ub-title)),
      utf8String        UTF8String      (SIZE (1..ub-title)),
      bmpString         BMPString       (SIZE (1..ub-title)) }

-- Naming attributes of type X520dnQualifier

id-at-dnQualifier       AttributeType ::= { id-at 46 }

X520dnQualifier ::=     PrintableString

-- Naming attributes of type X520countryName (digraph from IS 3166)

id-at-countryName       AttributeType ::= { id-at 6 }

X520countryName ::=     PrintableString (SIZE (2))

-- Naming attributes of type X520SerialNumber

id-at-serialNumber      AttributeType ::= { id-at 5 }

X520SerialNumber ::=    PrintableString (SIZE (1..ub-serial-number))

-- Naming attributes of type X520Pseudonym

id-at-pseudonym         AttributeType ::= { id-at 65 }

X520Pseudonym ::= CHOICE {
   teletexString     TeletexString   (SIZE (1..ub-pseudonym)),
   printableString   PrintableString (SIZE (1..ub-pseudonym)),
   universalString   UniversalString (SIZE (1..ub-pseudonym)),
   utf8String        UTF8String      (SIZE (1..ub-pseudonym)),
   bmpString         BMPString       (SIZE (1..ub-pseudonym)) }

-- Naming attributes of type DomainComponent (from RFC 2247)

id-domainComponent      AttributeType ::=
                          { 0 9 2342 19200300 100 1 25 }

DomainComponent ::=     IA5String

-- Legacy attributes

pkcs-9 OBJECT IDENTIFIER ::=
       { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 9 }

id-emailAddress          AttributeType ::= { pkcs-9 1 }

EmailAddress ::=         IA5String (SIZE (1..ub-emailaddress-length))

-- naming data types --

Name ::= CHOICE { -- only one possibility for now --
      rdnSequence  RDNSequence }

RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

DistinguishedName ::=   RDNSequence

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

-- Directory string type --

DirectoryString ::= CHOICE {
      teletexString             TeletexString   (SIZE (1..MAX)),
      printableString           PrintableString (SIZE (1..MAX)),
      universalString           UniversalString (SIZE (1..MAX)),
      utf8String              UTF8String      (SIZE (1..MAX)),
      bmpString               BMPString       (SIZE (1..MAX)) }

-- certificate and CRL specific structures begin 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      Time,
     notAfter       Time  }

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

UniqueIdentifier  ::=  BIT STRING

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

Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

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

-- 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              Time,
     nextUpdate              Time OPTIONAL,
     revokedCertificates     SEQUENCE OF SEQUENCE  {
          userCertificate         CertificateSerialNumber,
          revocationDate          Time,
          crlEntryExtensions      Extensions OPTIONAL
                                         -- if present, MUST be v2
                               }  OPTIONAL,
     crlExtensions           [0] Extensions OPTIONAL }
                                         -- if present, MUST be v2

-- Version, Time, CertificateSerialNumber, and Extensions were
-- defined earlier for use in the certificate structure

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

-- X.400 address syntax starts here

ORAddress ::= SEQUENCE {
   built-in-standard-attributes BuiltInStandardAttributes,
   built-in-domain-defined-attributes
                   BuiltInDomainDefinedAttributes OPTIONAL,
   -- see also teletex-domain-defined-attributes
   extension-attributes ExtensionAttributes OPTIONAL }

-- Built-in Standard Attributes

BuiltInStandardAttributes ::= SEQUENCE {
   country-name                  CountryName OPTIONAL,
   administration-domain-name    AdministrationDomainName OPTIONAL,
   network-address           [0] IMPLICIT NetworkAddress OPTIONAL,
     -- see also extended-network-address
   terminal-identifier       [1] IMPLICIT TerminalIdentifier OPTIONAL,
   private-domain-name       [2] PrivateDomainName OPTIONAL,
   organization-name         [3] IMPLICIT OrganizationName OPTIONAL,
     -- see also teletex-organization-name
   numeric-user-identifier   [4] IMPLICIT NumericUserIdentifier
                                 OPTIONAL,
   personal-name             [5] IMPLICIT PersonalName OPTIONAL,
     -- see also teletex-personal-name
   organizational-unit-names [6] IMPLICIT OrganizationalUnitNames
                                 OPTIONAL }
     -- see also teletex-organizational-unit-names

CountryName ::= [APPLICATION 1] CHOICE {
   x121-dcc-code         NumericString
                           (SIZE (ub-country-name-numeric-length)),
   iso-3166-alpha2-code  PrintableString
                           (SIZE (ub-country-name-alpha-length)) }

AdministrationDomainName ::= [APPLICATION 2] CHOICE {
   numeric   NumericString   (SIZE (0..ub-domain-name-length)),
   printable PrintableString (SIZE (0..ub-domain-name-length)) }

NetworkAddress ::= X121Address  -- see also extended-network-address

X121Address ::= NumericString (SIZE (1..ub-x121-address-length))

TerminalIdentifier ::= PrintableString (SIZE
(1..ub-terminal-id-length))

PrivateDomainName ::= CHOICE {
   numeric   NumericString   (SIZE (1..ub-domain-name-length)),
   printable PrintableString (SIZE (1..ub-domain-name-length)) }

OrganizationName ::= PrintableString
                            (SIZE (1..ub-organization-name-length))
  -- see also teletex-organization-name

NumericUserIdentifier ::= NumericString
                            (SIZE (1..ub-numeric-user-id-length))

PersonalName ::= SET {
   surname     [0] IMPLICIT PrintableString
                    (SIZE (1..ub-surname-length)),
   given-name  [1] IMPLICIT PrintableString
                    (SIZE (1..ub-given-name-length)) OPTIONAL,
   initials    [2] IMPLICIT PrintableString
                    (SIZE (1..ub-initials-length)) OPTIONAL,
   generation-qualifier [3] IMPLICIT PrintableString
                    (SIZE (1..ub-generation-qualifier-length))
                    OPTIONAL }
  -- see also teletex-personal-name

OrganizationalUnitNames ::= SEQUENCE SIZE (1..ub-organizational-units)
                             OF OrganizationalUnitName
  -- see also teletex-organizational-unit-names

OrganizationalUnitName ::= PrintableString (SIZE
                    (1..ub-organizational-unit-name-length))

-- Built-in Domain-defined Attributes

BuiltInDomainDefinedAttributes ::= SEQUENCE SIZE
                    (1..ub-domain-defined-attributes) OF
                    BuiltInDomainDefinedAttribute

BuiltInDomainDefinedAttribute ::= SEQUENCE {
   type PrintableString (SIZE
                   (1..ub-domain-defined-attribute-type-length)),
   value PrintableString (SIZE
                   (1..ub-domain-defined-attribute-value-length)) }

-- Extension Attributes

ExtensionAttributes ::= SET SIZE (1..ub-extension-attributes) OF
               ExtensionAttribute

ExtensionAttribute ::=  SEQUENCE {
   extension-attribute-type [0] IMPLICIT INTEGER
                   (0..ub-extension-attributes),
   extension-attribute-value [1]
                   ANY DEFINED BY extension-attribute-type }

-- Extension types and attribute values

common-name INTEGER ::= 1

CommonName ::= PrintableString (SIZE (1..ub-common-name-length))

teletex-common-name INTEGER ::= 2

TeletexCommonName ::= TeletexString (SIZE (1..ub-common-name-length))

teletex-organization-name INTEGER ::= 3

TeletexOrganizationName ::=
                TeletexString (SIZE (1..ub-organization-name-length))

teletex-personal-name INTEGER ::= 4

TeletexPersonalName ::= SET {
   surname     [0] IMPLICIT TeletexString
                    (SIZE (1..ub-surname-length)),
   given-name  [1] IMPLICIT TeletexString
                    (SIZE (1..ub-given-name-length)) OPTIONAL,
   initials    [2] IMPLICIT TeletexString
                    (SIZE (1..ub-initials-length)) OPTIONAL,
   generation-qualifier [3] IMPLICIT TeletexString
                    (SIZE (1..ub-generation-qualifier-length))
                    OPTIONAL }

teletex-organizational-unit-names INTEGER ::= 5

TeletexOrganizationalUnitNames ::= SEQUENCE SIZE
      (1..ub-organizational-units) OF TeletexOrganizationalUnitName

TeletexOrganizationalUnitName ::= TeletexString
                  (SIZE (1..ub-organizational-unit-name-length))

pds-name INTEGER ::= 7

PDSName ::= PrintableString (SIZE (1..ub-pds-name-length))

physical-delivery-country-name INTEGER ::= 8

PhysicalDeliveryCountryName ::= CHOICE {
   x121-dcc-code NumericString (SIZE
(ub-country-name-numeric-length)),
   iso-3166-alpha2-code PrintableString
                  (SIZE (ub-country-name-alpha-length)) }

postal-code INTEGER ::= 9

PostalCode ::= CHOICE {
   numeric-code NumericString (SIZE (1..ub-postal-code-length)),
   printable-code PrintableString (SIZE (1..ub-postal-code-length)) }

physical-delivery-office-name INTEGER ::= 10

PhysicalDeliveryOfficeName ::= PDSParameter

physical-delivery-office-number INTEGER ::= 11

PhysicalDeliveryOfficeNumber ::= PDSParameter

extension-OR-address-components INTEGER ::= 12

ExtensionORAddressComponents ::= PDSParameter

physical-delivery-personal-name INTEGER ::= 13

PhysicalDeliveryPersonalName ::= PDSParameter

physical-delivery-organization-name INTEGER ::= 14

PhysicalDeliveryOrganizationName ::= PDSParameter

extension-physical-delivery-address-components INTEGER ::= 15

ExtensionPhysicalDeliveryAddressComponents ::= PDSParameter

unformatted-postal-address INTEGER ::= 16

UnformattedPostalAddress ::= SET {
   printable-address SEQUENCE SIZE (1..ub-pds-physical-address-lines)
         OF PrintableString (SIZE (1..ub-pds-parameter-length))
         OPTIONAL,
   teletex-string TeletexString
         (SIZE (1..ub-unformatted-address-length)) OPTIONAL }

street-address INTEGER ::= 17

StreetAddress ::= PDSParameter

post-office-box-address INTEGER ::= 18

PostOfficeBoxAddress ::= PDSParameter

poste-restante-address INTEGER ::= 19

PosteRestanteAddress ::= PDSParameter

unique-postal-name INTEGER ::= 20

UniquePostalName ::= PDSParameter

local-postal-attributes INTEGER ::= 21

LocalPostalAttributes ::= PDSParameter

PDSParameter ::= SET {
   printable-string PrintableString
                (SIZE(1..ub-pds-parameter-length)) OPTIONAL,
   teletex-string TeletexString
                (SIZE(1..ub-pds-parameter-length)) OPTIONAL }

extended-network-address INTEGER ::= 22

ExtendedNetworkAddress ::= CHOICE {
   e163-4-address SEQUENCE {
      number      [0] IMPLICIT NumericString
                       (SIZE (1..ub-e163-4-number-length)),
      sub-address [1] IMPLICIT NumericString
                       (SIZE (1..ub-e163-4-sub-address-length))
                       OPTIONAL },
   psap-address [0] IMPLICIT PresentationAddress }

PresentationAddress ::= SEQUENCE {
    pSelector     [0] EXPLICIT OCTET STRING OPTIONAL,
    sSelector     [1] EXPLICIT OCTET STRING OPTIONAL,
    tSelector     [2] EXPLICIT OCTET STRING OPTIONAL,
    nAddresses    [3] EXPLICIT SET SIZE (1..MAX) OF OCTET STRING }

terminal-type  INTEGER ::= 23

TerminalType ::= INTEGER {
   telex (3),
   teletex (4),
   g3-facsimile (5),
   g4-facsimile (6),
   ia5-terminal (7),
   videotex (8) } (0..ub-integer-options)

-- Extension Domain-defined Attributes

teletex-domain-defined-attributes INTEGER ::= 6

TeletexDomainDefinedAttributes ::= SEQUENCE SIZE
   (1..ub-domain-defined-attributes) OF TeletexDomainDefinedAttribute

TeletexDomainDefinedAttribute ::= SEQUENCE {
        type TeletexString
               (SIZE (1..ub-domain-defined-attribute-type-length)),
        value TeletexString
               (SIZE (1..ub-domain-defined-attribute-value-length)) }

--  specifications of Upper Bounds MUST be regarded as mandatory
--  from Annex B of ITU-T X.411 Reference Definition of MTS Parameter
--  Upper Bounds

-- Upper Bounds
ub-name INTEGER ::= 32768
ub-common-name INTEGER ::= 64
ub-locality-name INTEGER ::= 128
ub-state-name INTEGER ::= 128
ub-organization-name INTEGER ::= 64
ub-organizational-unit-name INTEGER ::= 64
ub-title INTEGER ::= 64
ub-serial-number INTEGER ::= 64
ub-match INTEGER ::= 128
ub-emailaddress-length INTEGER ::= 128
ub-common-name-length INTEGER ::= 64
ub-country-name-alpha-length INTEGER ::= 2
ub-country-name-numeric-length INTEGER ::= 3
ub-domain-defined-attributes INTEGER ::= 4
ub-domain-defined-attribute-type-length INTEGER ::= 8
ub-domain-defined-attribute-value-length INTEGER ::= 128
ub-domain-name-length INTEGER ::= 16
ub-extension-attributes INTEGER ::= 256
ub-e163-4-number-length INTEGER ::= 15
ub-e163-4-sub-address-length INTEGER ::= 40
ub-generation-qualifier-length INTEGER ::= 3
ub-given-name-length INTEGER ::= 16
ub-initials-length INTEGER ::= 5
ub-integer-options INTEGER ::= 256
ub-numeric-user-id-length INTEGER ::= 32
ub-organization-name-length INTEGER ::= 64
ub-organizational-unit-name-length INTEGER ::= 32
ub-organizational-units INTEGER ::= 4
ub-pds-name-length INTEGER ::= 16
ub-pds-parameter-length INTEGER ::= 30
ub-pds-physical-address-lines INTEGER ::= 6
ub-postal-code-length INTEGER ::= 16
ub-pseudonym INTEGER ::= 128
ub-surname-length INTEGER ::= 40

ub-terminal-id-length INTEGER ::= 24
ub-unformatted-address-length INTEGER ::= 180
ub-x121-address-length INTEGER ::= 16

-- Note - upper bounds on string types, such as TeletexString, are
-- measured in characters.  Excepting PrintableString or IA5String, a
-- significantly greater number of octets will be required to hold
-- such a value.  As a minimum, 16 octets, or twice the specified
-- upper bound, whichever is the larger, should be allowed for
-- TeletexString.  For UTF8String or UniversalString at least four
-- times the upper bound should be allowed.

END

A.2 Implicitly Tagged Module, 1988 Syntax

PKIX1Implicit88 { iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

-- EXPORTS ALL --

IMPORTS
      id-pe, id-kp, id-qt-unotice, id-qt-cps,
      -- delete following line if "new" types are supported --
      BMPString, UTF8String,  -- end "new" types --
      ORAddress, Name, RelativeDistinguishedName,
      CertificateSerialNumber, Attribute, DirectoryString
      FROM PKIX1Explicit88 { iso(1) identified-organization(3)
            dod(6) internet(1) security(5) mechanisms(5) pkix(7)
            id-mod(0) id-pkix1-explicit(18) };

-- ISO arc for standard certificate and CRL extensions

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

-- authority key identifier OID and syntax

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

AuthorityKeyIdentifier ::= SEQUENCE {
    keyIdentifier             [0] KeyIdentifier            OPTIONAL,
    authorityCertIssuer       [1] GeneralNames             OPTIONAL,
    authorityCertSerialNumber [2] CertificateSerialNumber  OPTIONAL }
    -- authorityCertIssuer and authorityCertSerialNumber MUST both
    -- be present or both be absent

KeyIdentifier ::= OCTET STRING

-- subject key identifier OID and syntax

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

SubjectKeyIdentifier ::= KeyIdentifier

-- key usage extension OID and syntax

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),
     encipherOnly            (7),
     decipherOnly            (8) }

-- private key usage period extension OID and syntax

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

PrivateKeyUsagePeriod ::= SEQUENCE {
     notBefore       [0]     GeneralizedTime OPTIONAL,
     notAfter        [1]     GeneralizedTime OPTIONAL }
     -- either notBefore or notAfter MUST be present

-- certificate policies extension OID and syntax

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

anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificatePolicies 0 }

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  PolicyQualifierId,
       qualifier        ANY DEFINED BY policyQualifierId }

-- Implementations that recognize additional policy qualifiers MUST
-- augment the following definition for PolicyQualifierId

PolicyQualifierId ::=
    OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

-- CPS pointer qualifier

CPSuri ::= IA5String

-- user notice qualifier

UserNotice ::= SEQUENCE {
     noticeRef        NoticeReference OPTIONAL,
     explicitText     DisplayText OPTIONAL}

NoticeReference ::= SEQUENCE {
     organization     DisplayText,
     noticeNumbers    SEQUENCE OF INTEGER }

DisplayText ::= CHOICE {
     ia5String        IA5String      (SIZE (1..200)),
     visibleString    VisibleString  (SIZE (1..200)),
     bmpString        BMPString      (SIZE (1..200)),
     utf8String       UTF8String     (SIZE (1..200)) }

-- policy mapping extension OID and syntax

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

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

-- subject alternative name extension OID and syntax

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

SubjectAltName ::= GeneralNames

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

GeneralName ::= CHOICE {
     otherName                       [0]     AnotherName,
     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 }

-- AnotherName replaces OTHER-NAME ::= TYPE-IDENTIFIER, as
-- TYPE-IDENTIFIER is not supported in the '88 ASN.1 syntax

AnotherName ::= SEQUENCE {
     type-id    OBJECT IDENTIFIER,
     value      [0] EXPLICIT ANY DEFINED BY type-id }

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

-- issuer alternative name extension OID and syntax

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

-- basic constraints extension OID and syntax

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

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

-- name constraints extension OID and syntax

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)

-- policy constraints extension OID and syntax

id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }

PolicyConstraints ::= SEQUENCE {
     requireExplicitPolicy           [0] SkipCerts OPTIONAL,
     inhibitPolicyMapping            [1] SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

-- CRL distribution points extension OID and syntax

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

CRLDistributionPoints ::= 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),
     privilegeWithdrawn      (7),
     aACompromise            (8) }

-- extended key usage extension OID and syntax

id-ce-extKeyUsage OBJECT IDENTIFIER ::= {id-ce 37}

ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

KeyPurposeId ::= OBJECT IDENTIFIER

-- permit unspecified key uses

anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

-- extended key purpose OIDs

id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
id-kp-codeSigning            OBJECT IDENTIFIER ::= { id-kp 3 }
id-kp-emailProtection        OBJECT IDENTIFIER ::= { id-kp 4 }
id-kp-timeStamping           OBJECT IDENTIFIER ::= { id-kp 8 }
id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }

-- inhibit any policy OID and syntax

id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }

InhibitAnyPolicy ::= SkipCerts

-- freshest (delta)CRL extension OID and syntax

id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }

FreshestCRL ::= CRLDistributionPoints

-- authority info access

id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

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

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

-- subject info access

id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

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

-- CRL number extension OID and syntax

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

CRLNumber ::= INTEGER (0..MAX)

-- issuing distribution point extension OID and syntax

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,
     onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

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

BaseCRLNumber ::= CRLNumber

-- CRL reasons extension OID and syntax

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

CRLReason ::= ENUMERATED {
     unspecified             (0),
     keyCompromise           (1),
     cACompromise            (2),
     affiliationChanged      (3),
     superseded              (4),
     cessationOfOperation    (5),
     certificateHold         (6),
     removeFromCRL           (8),
     privilegeWithdrawn      (9),
     aACompromise           (10) }

-- certificate issuer CRL entry extension OID and syntax

id-ce-certificateIssuer OBJECT IDENTIFIER ::= { id-ce 29 }

CertificateIssuer ::= GeneralNames

-- hold instruction extension OID and syntax

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

HoldInstructionCode ::= OBJECT IDENTIFIER

-- ANSI x9 holdinstructions

-- ANSI x9 arc holdinstruction arc

holdInstruction OBJECT IDENTIFIER ::=
          {joint-iso-itu-t(2) member-body(2) us(840) x9cm(10040) 2}

-- ANSI X9 holdinstructions referenced by this standard

id-holdinstruction-none OBJECT IDENTIFIER  ::=
                {holdInstruction 1} -- deprecated

id-holdinstruction-callissuer OBJECT IDENTIFIER ::=
                {holdInstruction 2}

id-holdinstruction-reject OBJECT IDENTIFIER ::=
                {holdInstruction 3}

-- invalidity date CRL entry extension OID and syntax

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

InvalidityDate ::=  GeneralizedTime

END

Appendix B.  ASN.1 Notes

   CAs MUST force the serialNumber to be a non-negative integer, that
   is, the sign bit in the DER encoding of the INTEGER value MUST be
   zero - this can be done by adding a leading (leftmost) `00'H octet if
   necessary.  This removes a potential ambiguity in mapping between a
   string of octets and an integer value.

   As noted in section 4.1.2.2, serial numbers can be expected to
   contain long integers.  Certificate users MUST be able to handle
   serialNumber values up to 20 octets in length.  Conformant CAs MUST
   NOT use serialNumber values longer than 20 octets.

   As noted in section 5.2.3, CRL numbers can be expected to contain
   long integers.  CRL validators MUST be able to handle cRLNumber
   values up to 20 octets in length.  Conformant CRL issuers MUST NOT
   use cRLNumber values longer than 20 octets.

   The construct "SEQUENCE SIZE (1..MAX) OF" appears in several ASN.1
   constructs.  A valid ASN.1 sequence will have zero or more entries.
   The SIZE (1..MAX) construct constrains the sequence to have at least
   one entry.  MAX indicates the upper bound is unspecified.
   Implementations are free to choose an upper bound that suits their
   environment.

   The construct "positiveInt ::= INTEGER (0..MAX)" defines positiveInt
   as a subtype of INTEGER containing integers greater than or equal to
   zero.  The upper bound is unspecified.  Implementations are free to
   select an upper bound that suits their environment.

   The character string type PrintableString supports a very basic Latin
   character set: the lower case letters 'a' through 'z', upper case
   letters 'A' through 'Z', the digits '0' through '9', eleven special
   characters ' = ( ) + , - . / : ? and space.

   Implementers should note that the at sign ('@') and underscore ('_')
   characters are not supported by the ASN.1 type PrintableString.
   These characters often appear in internet addresses.  Such addresses
   MUST be encoded using an ASN.1 type that supports them.  They are
   usually encoded as IA5String in either the emailAddress attribute
   within a distinguished name or the rfc822Name field of GeneralName.
   Conforming implementations MUST NOT encode strings which include
   either the at sign or underscore character as PrintableString.

   The character string type TeletexString is a superset of
   PrintableString.  TeletexString supports a fairly standard (ASCII-
   like) Latin character set, Latin characters with non-spacing accents
   and Japanese characters.

   Named bit lists are BIT STRINGs where the values have been assigned
   names.  This specification makes use of named bit lists in the
   definitions for the key usage, CRL distribution points and freshest
   CRL certificate extensions, as well as the freshest CRL and issuing
   distribution point CRL extensions.  When DER encoding a named bit
   list, trailing zeroes MUST be omitted.  That is, the encoded value
   ends with the last named bit that is set to one.

   The character string type UniversalString supports any of the
   characters allowed by ISO 10646-1 [ISO 10646].  ISO 10646-1 is the
   Universal multiple-octet coded Character Set (UCS).  ISO 10646-1
   specifies the architecture and the "basic multilingual plane" -- a
   large standard character set which includes all major world character
   standards.

   The character string type UTF8String was introduced in the 1997
   version of ASN.1, and UTF8String was added to the list of choices for
   DirectoryString in the 2001 version of X.520 [X.520].  UTF8String is
   a universal type and has been assigned tag number 12.  The content of
   UTF8String was defined by RFC 2044 [RFC 2044] and updated in RFC 2279
   [RFC 2279].

   In anticipation of these changes, and in conformance with IETF Best
   Practices codified in RFC 2277 [RFC 2277], IETF Policy on Character
   Sets and Languages, this document includes UTF8String as a choice in
   DirectoryString and the CPS qualifier extensions.

   Implementers should note that the DER encoding of the SET OF values
   requires ordering of the encodings of the values.  In particular,
   this issue arises with respect to distinguished names.

   Implementers should note that the DER encoding of SET or SEQUENCE
   components whose value is the DEFAULT omit the component from the
   encoded certificate or CRL.  For example, a BasicConstraints
   extension whose cA value is FALSE would omit the cA boolean from the
   encoded certificate.

   Object Identifiers (OIDs) are used throughout this specification to
   identify certificate policies, public key and signature algorithms,
   certificate extensions, etc.  There is no maximum size for OIDs.
   This specification mandates support for OIDs which have arc elements
   with values that are less than 2^28, that is, they MUST be between 0
   and 268,435,455, inclusive.  This allows each arc element to be
   represented within a single 32 bit word.  Implementations MUST also
   support OIDs where the length of the dotted decimal (see [RFC 2252],
   section 4.1) string representation can be up to 100 bytes
   (inclusive).  Implementations MUST be able to handle OIDs with up to
   20 elements (inclusive).  CAs SHOULD NOT issue certificates which
   contain OIDs that exceed these requirements.  Likewise, CRL issuers
   SHOULD NOT issue CRLs which contain OIDs that exceed these
   requirements.

   Implementors are warned that the X.500 standards community has
   developed a series of extensibility rules.  These rules determine
   when an ASN.1 definition can be changed without assigning a new
   object identifier (OID).  For example, at least two extension
   definitions included in RFC 2459 [RFC 2459], the predecessor to this
   profile document, have different ASN.1 definitions in this
   specification, but the same OID is used.  If unknown elements appear
   within an extension, and the extension is not marked critical, those
   unknown elements ought to be ignored, as follows:

      (a)  ignore all unknown bit name assignments within a bit string;

      (b)  ignore all unknown named numbers in an ENUMERATED type or
      INTEGER type that is being used in the enumerated style, provided
      the number occurs as an optional element of a SET or SEQUENCE; and

      (c)  ignore all unknown elements in SETs, at the end of SEQUENCEs,
      or in CHOICEs where the CHOICE is itself an optional element of a
      SET or SEQUENCE.

   If an extension containing unexpected values is marked critical, the
   implementation MUST reject the certificate or CRL containing the
   unrecognized extension.

Appendix C.  Examples

   This section contains four examples: three certificates and a CRL.
   The first two certificates and the CRL comprise a minimal
   certification path.

   Section C.1 contains an annotated hex dump of a "self-signed"
   certificate issued by a CA whose distinguished name is
   cn=us,o=gov,ou=nist.  The certificate contains a DSA public key with
   parameters, and is signed by the corresponding DSA private key.

   Section C.2 contains an annotated hex dump of an end entity
   certificate.  The end entity certificate contains a DSA public key,
   and is signed by the private key corresponding to the "self-signed"
   certificate in section C.1.

   Section C.3 contains a dump of an end entity certificate which
   contains an RSA public key and is signed with RSA and MD5.  This
   certificate is not part of the minimal certification path.

   Section C.4 contains an annotated hex dump of a CRL.  The CRL is
   issued by the CA whose distinguished name is cn=us,o=gov,ou=nist and
   the list of revoked certificates includes the end entity certificate
   presented in C.2.

   The certificates were processed using Peter Gutman's dumpasn1 utility
   to generate the output.  The source for the dumpasn1 utility is
   available at <http://www.cs.auckland.ac.nz/~pgut001/dumpasn1.c>.  The
   binaries for the certificates and CRLs are available at
   <http://csrc.nist.gov/pki/pkixtools>.

C.1  Certificate

   This section contains an annotated hex dump of a 699 byte version 3
   certificate.  The certificate contains the following information:
   (a)  the serial number is 23 (17 hex);

   (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;
   (c)  the issuer's distinguished name is OU=NIST; O=gov; C=US
   (d)  and the subject's distinguished name is OU=NIST; O=gov; C=US
   (e)  the certificate was issued on June 30, 1997 and will expire on
   December 31, 1997;
   (f)  the certificate contains a 1024 bit DSA public key with
   parameters;
   (g)  the certificate contains a subject key identifier extension
   generated using method (1) of section 4.2.1.2; and
   (h)  the certificate is a CA certificate (as indicated through the
   basic constraints extension.)

  0 30  699: SEQUENCE {
  4 30  635:   SEQUENCE {
  8 A0    3:     [0] {
 10 02    1:       INTEGER 2
          :       }
 13 02    1:     INTEGER 17
 16 30    9:     SEQUENCE {
 18 06    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
          :       }
 27 30   42:     SEQUENCE {
 29 31   11:       SET {
 31 30    9:         SEQUENCE {
 33 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
 38 13    2:           PrintableString 'US'
          :           }
          :         }
 42 31   12:       SET {
 44 30   10:         SEQUENCE {
 46 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
 51 13    3:           PrintableString 'gov'
          :           }
          :         }
 56 31   13:       SET {
 58 30   11:         SEQUENCE {
 60 06    3:           OBJECT IDENTIFIER
          :             organizationalUnitName (2 5 4 11)
 65 13    4:           PrintableString 'NIST'
           :           }
           :         }
           :       }
 71 30   30:     SEQUENCE {
 73 17   13:       UTCTime '970630000000Z'
 88 17   13:       UTCTime '971231000000Z'
           :       }
103 30   42:     SEQUENCE {
105 31   11:       SET {

107 30    9:         SEQUENCE {
109 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
114 13    2:           PrintableString 'US'
           :           }
           :         }
118 31   12:       SET {
120 30   10:         SEQUENCE {
122 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
127 13    3:           PrintableString 'gov'
           :           }
           :         }
132 31   13:       SET {
134 30   11:         SEQUENCE {
136 06    3:           OBJECT IDENTIFIER
           :             organizationalUnitName (2 5 4 11)
141 13    4:           PrintableString 'NIST'
           :           }
           :         }
           :       }
147 30  440:     SEQUENCE {
151 30  300:       SEQUENCE {
155 06    7:         OBJECT IDENTIFIER dsa (1 2 840 10040 4 1)
164 30  287:         SEQUENCE {
168 02  129:           INTEGER
           :             00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC
           :             FB 95 32 AC 01 12 33 B9 E0 1C AD 90 9B BC
           :             48 54 9E F3 94 77 3C 2C 71 35 55 E6 FE 4F
           :             22 CB D5 D8 3E 89 93 33 4D FC BD 4F 41 64
           :             3E A2 98 70 EC 31 B4 50 DE EB F1 98 28 0A
           :             C9 3E 44 B3 FD 22 97 96 83 D0 18 A3 E3 BD
           :             35 5B FF EE A3 21 72 6A 7B 96 DA B9 3F 1E
           :             5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
           :             FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48
           :             63 FE 43
300 02   21:           INTEGER
           :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA
           :             55 F7 7D 57 74 81 E5
323 02  129:           INTEGER
           :             00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91
           :             C0 8E 47 F1 0A C3 01 47 C2 44 42 36 A9 92
           :             81 DE 57 C5 E0 68 86 58 00 7B 1F F9 9B 77
           :             A1 C5 10 A5 80 91 78 51 51 3C F6 FC FC CC
           :             46 C6 81 78 92 84 3D F4 93 3D 0C 38 7E 1A
           :             5B 99 4E AB 14 64 F6 0C 21 22 4E 28 08 9C
           :             92 B9 66 9F 40 E8 95 F6 D5 31 2A EF 39 A2
           :             62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
           :             F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE
           :             1E 57 18

           :           }
           :         }
455 03  133:       BIT STRING 0 unused bits, encapsulates {
459 02  129:           INTEGER
           :             00 B5 9E 1F 49 04 47 D1 DB F5 3A DD CA 04
           :             75 E8 DD 75 F6 9B 8A B1 97 D6 59 69 82 D3
           :             03 4D FD 3B 36 5F 4A F2 D1 4E C1 07 F5 D1
           :             2A D3 78 77 63 56 EA 96 61 4D 42 0B 7A 1D
           :             FB AB 91 A4 CE DE EF 77 C8 E5 EF 20 AE A6
           :             28 48 AF BE 69 C3 6A A5 30 F2 C2 B9 D9 82
           :             2B 7D D9 C4 84 1F DE 0D E8 54 D7 1B 99 2E
           :             B3 D0 88 F6 D6 63 9B A7 E2 0E 82 D4 3B 8A
           :             68 1B 06 56 31 59 0B 49 EB 99 A5 D5 81 41
           :             7B C9 55
           :           }
           :       }
591 A3   50:     [3] {
593 30   48:       SEQUENCE {
595 30   29:         SEQUENCE {
597 06    3:           OBJECT IDENTIFIER
           :             subjectKeyIdentifier (2 5 29 14)
602 04   22:           OCTET STRING, encapsulates {
604 04   20:               OCTET STRING
           :                 86 CA A5 22 81 62 EF AD 0A 89 BC AD 72 41
           :                 2C 29 49 F4 86 56
           :               }
           :           }
626 30   15:         SEQUENCE {
628 06    3:           OBJECT IDENTIFIER basicConstraints (2 5 29 19)
633 01    1:           BOOLEAN TRUE
636 04    5:           OCTET STRING, encapsulates {
638 30    3:               SEQUENCE {
640 01    1:                 BOOLEAN TRUE
           :                 }
           :               }
           :           }
           :         }
           :       }
           :     }
643 30    9:   SEQUENCE {
645 06    7:     OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
           :     }
654 03   47:   BIT STRING 0 unused bits, encapsulates {
657 30   44:       SEQUENCE {
659 02   20:         INTEGER
           :           43 1B CF 29 25 45 C0 4E 52 E7 7D D6 FC B1
           :           66 4C 83 CF 2D 77
681 02   20:         INTEGER

           :           0B 5B 9A 24 11 98 E8 F3 86 90 04 F6 08 A9
           :           E1 8D A5 CC 3A D4
           :         }
           :       }
           :   }

C.2  Certificate

   This section contains an annotated hex dump of a 730 byte version 3
   certificate.  The certificate contains the following information:
   (a)  the serial number is 18 (12 hex);
   (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;
   (c)  the issuer's distinguished name is OU=nist; O=gov; C=US
   (d)  and the subject's distinguished name is CN=Tim Polk; OU=nist;
   O=gov; C=US
   (e)  the certificate was valid from July 30, 1997 through December 1,
   1997;
   (f)  the certificate contains a 1024 bit DSA public key;
   (g)  the certificate is an end entity certificate, as the basic
   constraints extension is not present;
   (h)  the certificate contains an authority key identifier extension
   matching the subject key identifier of the certificate in Appendix
   C.1; and
   (i)  the certificate includes one alternative name - an RFC 822
   address of "wpolk@nist.gov".

     0 30  730: SEQUENCE {
     4 30  665:   SEQUENCE {
     8 A0    3:     [0] {
    10 02    1:       INTEGER 2
              :       }
    13 02    1:     INTEGER 18
    16 30    9:     SEQUENCE {
    18 06    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
              :       }
    27 30   42:     SEQUENCE {
    29 31   11:       SET {
    31 30    9:         SEQUENCE {
    33 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
    38 13    2:           PrintableString 'US'
              :           }
              :         }
    42 31   12:       SET {
    44 30   10:         SEQUENCE {
    46 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
    51 13    3:           PrintableString 'gov'
              :           }
              :         }

    56 31   13:       SET {
    58 30   11:         SEQUENCE {
    60 06    3:           OBJECT IDENTIFIER
              :             organizationalUnitName (2 5 4 11)
    65 13    4:           PrintableString 'NIST'
              :           }
              :         }
              :       }
    71 30   30:     SEQUENCE {
    73 17   13:       UTCTime '970730000000Z'
    88 17   13:       UTCTime '971201000000Z'
              :       }
   103 30   61:     SEQUENCE {
   105 31   11:       SET {
   107 30    9:         SEQUENCE {
   109 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
   114 13    2:           PrintableString 'US'
              :           }
              :         }
   118 31   12:       SET {
   120 30   10:         SEQUENCE {
   122 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
   127 13    3:           PrintableString 'gov'
              :           }
              :         }
   132 31   13:       SET {
   134 30   11:         SEQUENCE {
   136 06    3:           OBJECT IDENTIFIER
              :             organizationalUnitName (2 5 4 11)
   141 13    4:           PrintableString 'NIST'
              :           }
              :         }
   147 31   17:       SET {
   149 30   15:         SEQUENCE {
   151 06    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
   156 13    8:           PrintableString 'Tim Polk'
              :           }
              :         }
              :       }
   166 30  439:     SEQUENCE {
   170 30  300:       SEQUENCE {
   174 06    7:         OBJECT IDENTIFIER dsa (1 2 840 10040 4 1)
   183 30  287:         SEQUENCE {
   187 02  129:           INTEGER
              :             00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC
              :             FB 95 32 AC 01 12 33 B9 E0 1C AD 90 9B BC
              :             48 54 9E F3 94 77 3C 2C 71 35 55 E6 FE 4F
              :             22 CB D5 D8 3E 89 93 33 4D FC BD 4F 41 64

              :             3E A2 98 70 EC 31 B4 50 DE EB F1 98 28 0A
              :             C9 3E 44 B3 FD 22 97 96 83 D0 18 A3 E3 BD
              :             35 5B FF EE A3 21 72 6A 7B 96 DA B9 3F 1E
              :             5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
              :             FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48
              :             63 FE 43
   319 02   21:           INTEGER
              :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA
              :             55 F7 7D 57 74 81 E5
   342 02  129:           INTEGER
              :             00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91
              :             C0 8E 47 F1 0A C3 01 47 C2 44 42 36 A9 92
              :             81 DE 57 C5 E0 68 86 58 00 7B 1F F9 9B 77
              :             A1 C5 10 A5 80 91 78 51 51 3C F6 FC FC CC
              :             46 C6 81 78 92 84 3D F4 93 3D 0C 38 7E 1A
              :             5B 99 4E AB 14 64 F6 0C 21 22 4E 28 08 9C
              :             92 B9 66 9F 40 E8 95 F6 D5 31 2A EF 39 A2
              :             62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
              :             F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE
              :             1E 57 18
              :           }
              :         }
   474 03  132:       BIT STRING 0 unused bits, encapsulates {
   478 02  128:           INTEGER
              :             30 B6 75 F7 7C 20 31 AE 38 BB 7E 0D 2B AB
              :             A0 9C 4B DF 20 D5 24 13 3C CD 98 E5 5F 6C
              :             B7 C1 BA 4A BA A9 95 80 53 F0 0D 72 DC 33
              :             37 F4 01 0B F5 04 1F 9D 2E 1F 62 D8 84 3A
              :             9B 25 09 5A 2D C8 46 8E 2B D4 F5 0D 3B C7
              :             2D C6 6C B9 98 C1 25 3A 44 4E 8E CA 95 61
              :             35 7C CE 15 31 5C 23 13 1E A2 05 D1 7A 24
              :             1C CB D3 72 09 90 FF 9B 9D 28 C0 A1 0A EC
              :             46 9F 0D B8 D0 DC D0 18 A6 2B 5E F9 8F B5
              :             95 BE
              :           }
              :       }
   609 A3   62:     [3] {
   611 30   60:       SEQUENCE {
   613 30   25:         SEQUENCE {
   615 06    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
   620 04   18:           OCTET STRING, encapsulates {
   622 30   16:               SEQUENCE {
   624 81   14:                 [1] 'wpolk@nist.gov'
              :                 }
              :               }
              :           }
   640 30   31:         SEQUENCE {
   642 06    3:           OBJECT IDENTIFIER

              :             authorityKeyIdentifier (2 5 29 35)
   647 04   24:           OCTET STRING, encapsulates {
   649 30   22:               SEQUENCE {
   651 80   20:                 [0]
              :                   86 CA A5 22 81 62 EF AD 0A 89 BC AD 72
              :                   41 2C 29 49 F4 86 56
              :                 }
              :               }
              :           }
              :         }
              :       }
              :     }
   673 30    9:   SEQUENCE {
   675 06    7:     OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
              :     }
   684 03   48:   BIT STRING 0 unused bits, encapsulates {
   687 30   45:       SEQUENCE {
   689 02   20:         INTEGER
              :           36 97 CB E3 B4 2C E1 BB 61 A9 D3 CC 24 CC
              :           22 92 9F F4 F5 87
   711 02   21:         INTEGER
              :           00 AB C9 79 AF D2 16 1C A9 E3 68 A9 14 10
              :           B4 A0 2E FF 22 5A 73
              :         }
              :       }
              :   }

C.3  End Entity Certificate Using RSA

   This section contains an annotated hex dump of a 654 byte version 3
   certificate.  The certificate contains the following information:
   (a)  the serial number is 256;
   (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
   (c)  the issuer's distinguished name is OU=NIST; O=gov; C=US
   (d)  and the subject's distinguished name is CN=Tim Polk; OU=NIST;
   O=gov; C=US
   (e)  the certificate was issued on May 21, 1996 at 09:58:26 and
   expired on May 21, 1997 at 09:58:26;
   (f)  the certificate contains a 1024 bit RSA public key;
   (g)  the certificate is an end entity certificate (not a CA
   certificate);
   (h)  the certificate includes an alternative subject name of
   "<http://www.itl.nist.gov/div893/staff/polk/index.html>" and an
   alternative issuer name of "<http://www.nist.gov/>" - both are URLs;
   (i)  the certificate include an authority key identifier extension
   and a certificate policies extension specifying the policy OID
   2.16.840.1.101.3.2.1.48.9; and

   (j)  the certificate includes a critical key usage extension
   specifying that the public key is intended for verification of
   digital signatures.

  0 30  654: SEQUENCE {
  4 30  503:   SEQUENCE {
  8 A0    3:     [0] {
 10 02    1:       INTEGER 2
           :       }
 13 02    2:     INTEGER 256
 17 30   13:     SEQUENCE {
 19 06    9:       OBJECT IDENTIFIER
           :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
 30 05    0:       NULL
           :       }
 32 30   42:     SEQUENCE {
 34 31   11:       SET {
 36 30    9:         SEQUENCE {
 38 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
 43 13    2:           PrintableString 'US'
           :           }
           :         }
 47 31   12:       SET {
 49 30   10:         SEQUENCE {
 51 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
 56 13    3:           PrintableString 'gov'
           :           }
           :         }
 61 31   13:       SET {
 63 30   11:         SEQUENCE {
 65 06    3:           OBJECT IDENTIFIER
           :             organizationalUnitName (2 5 4 11)
 70 13    4:           PrintableString 'NIST'
           :           }
           :         }
           :       }
 76 30   30:     SEQUENCE {
 78 17   13:       UTCTime '960521095826Z'
 93 17   13:       UTCTime '970521095826Z'
           :       }
108 30   61:     SEQUENCE {
110 31   11:       SET {
112 30    9:         SEQUENCE {
114 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
119 13    2:           PrintableString 'US'
           :           }
           :         }
123 31   12:       SET {

125 30   10:         SEQUENCE {
127 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
132 13    3:           PrintableString 'gov'
           :           }
           :         }
137 31   13:       SET {
139 30   11:         SEQUENCE {
141 06    3:           OBJECT IDENTIFIER
           :             organizationalUnitName (2 5 4 11)
146 13    4:           PrintableString 'NIST'
           :           }
           :         }
152 31   17:       SET {
154 30   15:         SEQUENCE {
156 06    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
161 13    8:           PrintableString 'Tim Polk'
           :           }
           :         }
           :       }
171 30  159:     SEQUENCE {
174 30   13:       SEQUENCE {
176 06    9:         OBJECT IDENTIFIER
           :           rsaEncryption (1 2 840 113549 1 1 1)
187 05    0:         NULL
           :         }
189 03  141:       BIT STRING 0 unused bits, encapsulates {
193 30  137:           SEQUENCE {
196 02  129:             INTEGER
           :               00 E1 6A E4 03 30 97 02 3C F4 10 F3 B5 1E
           :               4D 7F 14 7B F6 F5 D0 78 E9 A4 8A F0 A3 75
           :               EC ED B6 56 96 7F 88 99 85 9A F2 3E 68 77
           :               87 EB 9E D1 9F C0 B4 17 DC AB 89 23 A4 1D
           :               7E 16 23 4C 4F A8 4D F5 31 B8 7C AA E3 1A
           :               49 09 F4 4B 26 DB 27 67 30 82 12 01 4A E9
           :               1A B6 C1 0C 53 8B 6C FC 2F 7A 43 EC 33 36
           :               7E 32 B2 7B D5 AA CF 01 14 C6 12 EC 13 F2
           :               2D 14 7A 8B 21 58 14 13 4C 46 A3 9A F2 16
           :               95 FF 23
328 02    3:             INTEGER 65537
           :             }
           :           }
           :       }
333 A3  175:     [3] {
336 30  172:       SEQUENCE {
339 30   63:         SEQUENCE {
341 06    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
346 04   56:           OCTET STRING, encapsulates {
348 30   54:               SEQUENCE {

350 86   52:                 [6]
           :                   'http://www.itl.nist.gov/div893/staff/'
           :                   'polk/index.html'
           :                 }
           :               }
           :           }
404 30   31:         SEQUENCE {
406 06    3:           OBJECT IDENTIFIER issuerAltName (2 5 29 18)
411 04   24:           OCTET STRING, encapsulates {
413 30   22:               SEQUENCE {
415 86   20:                 [6] 'http://www.nist.gov/'
           :                 }
           :               }
           :           }
437 30   31:         SEQUENCE {
439 06    3:           OBJECT IDENTIFIER
           :             authorityKeyIdentifier (2 5 29 35)
444 04   24:           OCTET STRING, encapsulates {
446 30   22:               SEQUENCE {
448 80   20:                 [0]
           :                   08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E
           :                   70 6A 4A 20 84 2C 32
           :                 }
           :               }
           :           }
470 30   23:         SEQUENCE {
472 06    3:           OBJECT IDENTIFIER
           :             certificatePolicies (2 5 29 32)
477 04   16:           OCTET STRING, encapsulates {
479 30   14:               SEQUENCE {
481 30   12:                 SEQUENCE {
483 06   10:                   OBJECT IDENTIFIER
           :                            '2 16 840 1 101 3 2 1 48 9'
           :                   }
           :                 }
           :               }
           :           }
495 30   14:         SEQUENCE {
497 06    3:           OBJECT IDENTIFIER keyUsage (2 5 29 15)
502 01    1:           BOOLEAN TRUE
505 04    4:           OCTET STRING, encapsulates {
507 03    2:               BIT STRING 7 unused bits
           :                 '1'B (bit 0)
           :               }
           :           }
           :         }
           :       }
           :     }

511 30   13:   SEQUENCE {
513 06    9:     OBJECT IDENTIFIER
           :       sha1withRSAEncryption (1 2 840 113549 1 1 5)
524 05    0:     NULL
           :     }
526 03  129:   BIT STRING 0 unused bits
           :     1E 07 77 6E 66 B5 B6 B8 57 F0 03 DC 6F 77
           :     6D AF 55 1D 74 E5 CE 36 81 FC 4B C5 F4 47
           :     82 C4 0A 25 AA 8D D6 7D 3A 89 AB 44 34 39
           :     F6 BD 61 1A 78 85 7A B8 1E 92 A2 22 2F CE
           :     07 1A 08 8E F1 46 03 59 36 4A CB 60 E6 03
           :     40 01 5B 2A 44 D6 E4 7F EB 43 5E 74 0A E6
           :     E4 F9 3E E1 44 BE 1F E7 5F 5B 2C 41 8D 08
           :     BD 26 FE 6A A6 C3 2F B2 3B 41 12 6B C1 06
           :     8A B8 4C 91 59 EB 2F 38 20 2A 67 74 20 0B
           :     77 F3
           :   }

C.4  Certificate Revocation List

   This section contains an annotated hex dump of a version 2 CRL with
   one extension (cRLNumber).  The CRL was issued by OU=NIST; O=gov;
   C=US on August 7, 1997; the next scheduled issuance was September 7,
   1997.  The CRL includes one revoked certificates: serial number 18
   (12 hex), which was revoked on July 31, 1997 due to keyCompromise.
   The CRL itself is number 18, and it was signed with DSA and SHA-1.

  0 30  203: SEQUENCE {
  3 30  140:   SEQUENCE {
  6 02    1:     INTEGER 1
  9 30    9:     SEQUENCE {
 11 06    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
           :       }
 20 30   42:     SEQUENCE {
 22 31   11:       SET {
 24 30    9:         SEQUENCE {
 26 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
 31 13    2:           PrintableString 'US'
           :           }
           :         }
 35 31   12:       SET {
 37 30   10:         SEQUENCE {
 39 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
 44 13    3:           PrintableString 'gov'
           :           }
           :         }
 49 31   13:       SET {
 51 30   11:         SEQUENCE {

 53 06    3:           OBJECT IDENTIFIER
           :             organizationalUnitName (2 5 4 11)
 58 13    4:           PrintableString 'NIST'
           :           }
           :         }
           :       }
 64 17   13:     UTCTime '970807000000Z'
 79 17   13:     UTCTime '970907000000Z'
 94 30   34:     SEQUENCE {
 96 30   32:       SEQUENCE {
 98 02    1:         INTEGER 18
101 17   13:         UTCTime '970731000000Z'
116 30   12:         SEQUENCE {
118 30   10:           SEQUENCE {
120 06    3:             OBJECT IDENTIFIER cRLReason (2 5 29 21)
125 04    3:             OCTET STRING, encapsulates {
127 0A    1:                 ENUMERATED 1
           :                 }
           :             }
           :           }
           :         }
           :       }
130 A0   14:     [0] {
132 30   12:       SEQUENCE {
134 30   10:         SEQUENCE {
136 06    3:           OBJECT IDENTIFIER cRLNumber (2 5 29 20)
141 04    3:           OCTET STRING, encapsulates {
143 02    1:               INTEGER 12
           :               }
           :           }
           :         }
           :       }
           :     }
146 30    9:   SEQUENCE {
148 06    7:     OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
           :     }
157 03   47:   BIT STRING 0 unused bits, encapsulates {
160 30   44:       SEQUENCE {
162 02   20:         INTEGER
           :           22 4E 9F 43 BA 95 06 34 F2 BB 5E 65 DB A6
           :           80 05 C0 3A 29 47
184 02   20:         INTEGER
           :           59 1A 57 C9 82 D7 02 21 14 C3 D4 0B 32 1B
           :           96 16 B1 1F 46 5A
           :         }
           :       }
           :   }

Author Addresses

   Russell Housley
   RSA Laboratories
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   EMail:  rhousley@rsasecurity.com

   Warwick Ford
   VeriSign, Inc.
   401 Edgewater Place
   Wakefield, MA 01880
   USA

   EMail:  wford@verisign.com

   Tim Polk
   NIST
   Building 820, Room 426
   Gaithersburg, MD 20899
   USA

   EMail:  wpolk@nist.gov

   David Solo
   Citigroup
   909 Third Ave, 16th Floor
   New York, NY 10043
   USA

   EMail:  dsolo@alum.mit.edu

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