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rfc:rfc5280

Network Working Group D. Cooper Request for Comments: 5280 NIST Obsoletes: 3280, 4325, 4630 S. Santesson Category: Standards Track Microsoft

                                                            S. Farrell
                                                Trinity College Dublin
                                                             S. Boeyen
                                                               Entrust
                                                            R. Housley
                                                        Vigil Security
                                                               W. Polk
                                                                  NIST
                                                              May 2008
       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.

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 is 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 along with standard and Internet-specific
 extensions.  An algorithm for X.509 certification path validation is
 described.  An ASN.1 module and examples are provided in the
 appendices.

Cooper, et al. Standards Track [Page 1] RFC 5280 PKIX Certificate and CRL Profile May 2008

Table of Contents

 1. Introduction ....................................................4
 2. Requirements and Assumptions ....................................6
    2.1. Communication and Topology .................................7
    2.2. Acceptability Criteria .....................................7
    2.3. User Expectations ..........................................7
    2.4. Administrator Expectations .................................8
 3. Overview of Approach ............................................8
    3.1. X.509 Version 3 Certificate ................................9
    3.2. Certification Paths and Trust .............................10
    3.3. Revocation ................................................13
    3.4. Operational Protocols .....................................14
    3.5. Management Protocols ......................................14
 4. Certificate and Certificate Extensions Profile .................16
    4.1. Basic Certificate Fields ..................................16
         4.1.1. Certificate Fields .................................17
                4.1.1.1. tbsCertificate ............................18
                4.1.1.2. signatureAlgorithm ........................18
                4.1.1.3. signatureValue ............................18
         4.1.2. TBSCertificate .....................................18
                4.1.2.1. Version ...................................19
                4.1.2.2. Serial Number .............................19
                4.1.2.3. Signature .................................19
                4.1.2.4. Issuer ....................................20
                4.1.2.5. Validity ..................................22
                         4.1.2.5.1. UTCTime ........................23
                         4.1.2.5.2. GeneralizedTime ................23
                4.1.2.6. Subject ...................................23
                4.1.2.7. Subject Public Key Info ...................25
                4.1.2.8. Unique Identifiers ........................25
                4.1.2.9. Extensions ................................26
    4.2. Certificate Extensions ....................................26
         4.2.1. Standard Extensions ................................27
                4.2.1.1. Authority Key Identifier ..................27
                4.2.1.2. Subject Key Identifier ....................28
                4.2.1.3. Key Usage .................................29
                4.2.1.4. Certificate Policies ......................32
                4.2.1.5. Policy Mappings ...........................35
                4.2.1.6. Subject Alternative Name ..................35
                4.2.1.7. Issuer Alternative Name ...................38
                4.2.1.8. Subject Directory Attributes ..............39
                4.2.1.9. Basic Constraints .........................39
                4.2.1.10. Name Constraints .........................40
                4.2.1.11. Policy Constraints .......................43
                4.2.1.12. Extended Key Usage .......................44
                4.2.1.13. CRL Distribution Points ..................45
                4.2.1.14. Inhibit anyPolicy ........................48

Cooper, et al. Standards Track [Page 2] RFC 5280 PKIX Certificate and CRL Profile May 2008

                4.2.1.15. Freshest CRL (a.k.a. Delta CRL
                          Distribution Point) ......................48
         4.2.2. Private Internet Extensions ........................49
                4.2.2.1. Authority Information Access ..............49
                4.2.2.2. Subject Information Access ................51
 5. CRL and CRL Extensions Profile .................................54
    5.1. CRL Fields ................................................55
         5.1.1. CertificateList Fields .............................56
                5.1.1.1. tbsCertList ...............................56
                5.1.1.2. signatureAlgorithm ........................57
                5.1.1.3. signatureValue ............................57
         5.1.2. Certificate List "To Be Signed" ....................58
                5.1.2.1. Version ...................................58
                5.1.2.2. Signature .................................58
                5.1.2.3. Issuer Name ...............................58
                5.1.2.4. This Update ...............................58
                5.1.2.5. Next Update ...............................59
                5.1.2.6. Revoked Certificates ......................59
                5.1.2.7. Extensions ................................60
    5.2. CRL Extensions ............................................60
         5.2.1. Authority Key Identifier ...........................60
         5.2.2. Issuer Alternative Name ............................60
         5.2.3. CRL Number .........................................61
         5.2.4. Delta CRL Indicator ................................62
         5.2.5. Issuing Distribution Point .........................65
         5.2.6. Freshest CRL (a.k.a. Delta CRL Distribution
                Point) .............................................67
         5.2.7. Authority Information Access .......................67
    5.3. CRL Entry Extensions ......................................69
         5.3.1. Reason Code ........................................69
         5.3.2. Invalidity Date ....................................70
         5.3.3. Certificate Issuer .................................70
 6. Certification Path Validation ..................................71
    6.1. Basic Path Validation .....................................72
         6.1.1. Inputs .............................................75
         6.1.2. Initialization .....................................77
         6.1.3. Basic Certificate Processing .......................80
         6.1.4. Preparation for Certificate i+1 ....................84
         6.1.5. Wrap-Up Procedure ..................................87
         6.1.6. Outputs ............................................89
    6.2. Using the Path Validation Algorithm .......................89
    6.3. CRL Validation ............................................90
         6.3.1. Revocation Inputs ..................................91
         6.3.2. Initialization and Revocation State Variables ......91
         6.3.3. CRL Processing .....................................92
 7. Processing Rules for Internationalized Names ...................95
    7.1. Internationalized Names in Distinguished Names ............96
    7.2. Internationalized Domain Names in GeneralName .............97

Cooper, et al. Standards Track [Page 3] RFC 5280 PKIX Certificate and CRL Profile May 2008

    7.3. Internationalized Domain Names in Distinguished Names .....98
    7.4. Internationalized Resource Identifiers ....................98
    7.5. Internationalized Electronic Mail Addresses ..............100
 8. Security Considerations .......................................100
 9. IANA Considerations ...........................................105
 10. Acknowledgments ..............................................105
 11. References ...................................................105
    11.1. Normative References ....................................105
    11.2. Informative References ..................................107
 Appendix A.  Pseudo-ASN.1 Structures and OIDs ....................110
    A.1. Explicitly Tagged Module, 1988 Syntax ....................110
    A.2. Implicitly Tagged Module, 1988 Syntax ....................125
 Appendix B. ASN.1 Notes ..........................................133
 Appendix C. Examples .............................................136
    C.1. RSA Self-Signed Certificate ..............................137
    C.2. End Entity Certificate Using RSA .........................140
    C.3. End Entity Certificate Using DSA .........................143
    C.4. Certificate Revocation List ..............................147

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
 that 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 is 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 that 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.

Cooper, et al. Standards Track [Page 4] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Procedures for identification and encoding of public key materials
 and digital signatures are defined in [RFC3279], [RFC4055], and
 [RFC4491].  Implementations of this specification are not required to
 use any particular cryptographic algorithms.  However, conforming
 implementations that use the algorithms identified in [RFC3279],
 [RFC4055], and [RFC4491] MUST identify and encode the public key
 materials and digital signatures as described in those
 specifications.
 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 conforming certificates and a conforming CRL.
 This specification obsoletes [RFC3280].  Differences from RFC 3280
 are summarized below:
  • Enhanced support for internationalized names is specified in

Section 7, with rules for encoding and comparing

      Internationalized Domain Names, Internationalized Resource
      Identifiers (IRIs), and distinguished names.  These rules are
      aligned with comparison rules established in current RFCs,
      including [RFC3490], [RFC3987], and [RFC4518].
  • Sections 4.1.2.4 and 4.1.2.6 incorporate the conditions for

continued use of legacy text encoding schemes that were

      specified in [RFC4630].  Where in use by an established PKI,
      transition to UTF8String could cause denial of service based on
      name chaining failures or incorrect processing of name
      constraints.
  • Section 4.2.1.4 in RFC 3280, which specified the

privateKeyUsagePeriod certificate extension but deprecated its

      use, was removed.  Use of this ISO standard extension is neither
      deprecated nor recommended for use in the Internet PKI.
  • Section 4.2.1.5 recommends marking the policy mappings extension

as critical. RFC 3280 required that the policy mappings

      extension be marked as non-critical.
  • Section 4.2.1.11 requires marking the policy constraints

extension as critical. RFC 3280 permitted the policy

      constraints extension to be marked as critical or non-critical.
  • The Authority Information Access (AIA) CRL extension, as

specified in [RFC4325], was added as Section 5.2.7.

Cooper, et al. Standards Track [Page 5] RFC 5280 PKIX Certificate and CRL Profile May 2008

  • Sections 5.2 and 5.3 clarify the rules for handling unrecognized

CRL extensions and CRL entry extensions, respectively.

  • Section 5.3.2 in RFC 3280, which specified the

holdInstructionCode CRL entry extension, was removed.

  • The path validation algorithm specified in Section 6 no longer

tracks the criticality of the certificate policies extensions in

      a chain of certificates.  In RFC 3280, this information was
      returned to a relying party.
  • The Security Considerations section addresses the risk of

circular dependencies arising from the use of https or similar

      schemes in the CRL distribution points, authority information
      access, or subject information access extensions.
  • The Security Considerations section addresses risks associated

with name ambiguity.

  • The Security Considerations section references RFC 4210 for

procedures to signal changes in CA operations.

 The ASN.1 modules in Appendix A are unchanged from RFC 3280, except
 that ub-emailaddress-length was changed from 128 to 255 in order to
 align with PKCS #9 [RFC2985].
 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 [RFC2119].

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

Cooper, et al. Standards Track [Page 6] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 [X.500] or a Lightweight Directory Access Protocol (LDAP)
 directory system [RFC4510].  The profile does not prohibit the use of
 an X.500 directory or an 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

Cooper, et al. Standards Track [Page 7] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 that shield the user from many malicious actions, and
 applications that 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 Public-Key Infrastructure using X.509 (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: a system that generates and signs CRLs; and
 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.
 CAs are responsible for indicating the revocation status of the
 certificates that they issue.  Revocation status information may be
 provided using the Online Certificate Status Protocol (OCSP)
 [RFC2560], certificate revocation lists (CRLs), or some other
 mechanism.  In general, when revocation status information is
 provided using CRLs, the CA is also the CRL issuer.  However, a CA
 may delegate the responsibility for issuing CRLs to a different
 entity.
 Note that an Attribute Authority (AA) might also choose to delegate
 the publication of CRLs to a CRL issuer.

Cooper, et al. Standards Track [Page 8] RFC 5280 PKIX Certificate and CRL Profile May 2008

 +---+
 | 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

Cooper, et al. Standards Track [Page 9] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 [RFC1422].  The experience gained in attempts to
 deploy RFC 1422 made it clear that the v1 and v2 certificate formats
 were deficient in several respects.  Most importantly, more fields
 were needed to carry information that PEM design and implementation
 experience had proven necessary.  In response to these new
 requirements, the 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

Cooper, et al. Standards Track [Page 10] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.

Cooper, et al. Standards Track [Page 11] RFC 5280 PKIX Certificate and CRL Profile May 2008

 RFC 1422 uses the X.509 v1 certificate format.  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.
 X.509 v3 also includes an extension that identifies the subject of a
 certificate as being either a CA or an end entity, reducing the
 reliance on out-of-band information demanded in PEM.
 This specification covers two classes of certificates: CA
 certificates and end entity certificates.  CA certificates may be
 further divided into three classes: cross-certificates, self-issued

Cooper, et al. Standards Track [Page 12] RFC 5280 PKIX Certificate and CRL Profile May 2008

 certificates, and self-signed certificates.  Cross-certificates are
 CA certificates in which the issuer and subject are different
 entities.  Cross-certificates describe a trust relationship between
 the two CAs.  Self-issued certificates are CA certificates in which
 the issuer and subject are the same entity.  Self-issued certificates
 are generated to support changes in policy or operations.  Self-
 signed certificates are self-issued certificates where the digital
 signature may be verified by the public key bound into the
 certificate.  Self-signed certificates are used to convey a public
 key for use to begin certification paths.  End entity certificates
 are issued to subjects that are not authorized to issue certificates.

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 that 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

Cooper, et al. Standards Track [Page 13] RFC 5280 PKIX Certificate and CRL Profile May 2008

 revocation is reported now, that revocation will not be reliably
 notified to certificate-using systems until all currently issued CRLs
 are scheduled to be 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 that cross-certify each
 other.  The set of functions that 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.

Cooper, et al. Standards Track [Page 14] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (b)  initialization:  Before a client system can operate securely,
         it is necessary to install key materials that 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 that 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.

Cooper, et al. Standards Track [Page 15] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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., email, 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

Cooper, et al. Standards Track [Page 16] RFC 5280 PKIX Certificate and CRL Profile May 2008

      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
                  -- contains the DER encoding of an ASN.1 value
                  -- corresponding to the extension type identified
                  -- by extnID
      }
 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.

Cooper, et al. Standards Track [Page 17] RFC 5280 PKIX Certificate and CRL Profile May 2008

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.
 [RFC3279], [RFC4055], and [RFC4491] list 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 the algorithms listed in [RFC3279], [RFC4055], and [RFC4491].
 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 that issued it.  Every
 TBSCertificate contains the names of the subject and issuer, a public

Cooper, et al. Standards Track [Page 18] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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, the
 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.  Conforming 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

Cooper, et al. Standards Track [Page 19] RFC 5280 PKIX Certificate and CRL Profile May 2008

 4.1.1.2).  The contents of the optional parameters field will vary
 according to the algorithm identified.  [RFC3279], [RFC4055], and
 [RFC4491] list supported signature algorithms, but other signature
 algorithms MAY also be supported.

4.1.2.4. Issuer

 The issuer field identifies the entity that 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 { -- only one possibility for now --
   rdnSequence  RDNSequence }
 RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
 RelativeDistinguishedName ::=
   SET SIZE (1..MAX) 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.  CAs
 conforming to this profile MUST use either the PrintableString or
 UTF8String encoding of DirectoryString, with two exceptions.  When
 CAs have previously issued certificates with issuer fields with
 attributes encoded using TeletexString, BMPString, or
 UniversalString, then the CA MAY continue to use these encodings of
 the DirectoryString to preserve backward compatibility.  Also, new

Cooper, et al. Standards Track [Page 20] RFC 5280 PKIX Certificate and CRL Profile May 2008

 CAs that are added to a domain where existing CAs issue certificates
 with issuer fields with attributes encoded using TeletexString,
 BMPString, or UniversalString MAY encode attributes that they share
 with the existing CAs using the same encodings as the existing CAs
 use.
 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 [RFC4519].
 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 extensions.  Implementations are not required to

Cooper, et al. Standards Track [Page 21] RFC 5280 PKIX Certificate and CRL Profile May 2008

 convert such names into DNS names.  The syntax and associated OID for
 this attribute type are provided in the ASN.1 modules in Appendix A.
 Rules for encoding internationalized domain names for use with the
 domainComponent attribute type are specified in Section 7.3.
 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.  Rules for comparing distinguished names are specified
 in Section 7.1.  If the names in the issuer and subject field in a
 certificate match according to the rules specified in Section 7.1,
 then the certificate is self-issued.

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.
 Conforming applications MUST be able to process validity dates that
 are encoded in either UTCTime or GeneralizedTime.
 The validity period for a certificate is the period of time from
 notBefore through notAfter, inclusive.
 In some situations, devices are given certificates for which no good
 expiration date can be assigned.  For example, a device could be
 issued a certificate that binds its model and serial number to its
 public key; such a certificate is intended to be used for the entire
 lifetime of the device.
 To indicate that a certificate has no well-defined expiration date,
 the notAfter SHOULD be assigned the GeneralizedTime value of
 99991231235959Z.
 When the issuer will not be able to maintain status information until
 the notAfter date (including when the notAfter date is
 99991231235959Z), the issuer MUST ensure that no valid certification
 path exists for the certificate after maintenance of status

Cooper, et al. Standards Track [Page 22] RFC 5280 PKIX Certificate and CRL Profile May 2008

 information is terminated.  This may be accomplished by expiration or
 revocation of all CA certificates containing the public key used to
 verify the signature on the certificate and discontinuing use of the
 public key used to verify the signature on the certificate as a trust
 anchor.

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 in
 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 in 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 Section 4.2.1.9, 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 Section 4.2.1.3, is present and the value of cRLSign is TRUE),

Cooper, et al. Standards Track [Page 23] RFC 5280 PKIX Certificate and CRL Profile May 2008

 then the subject field MUST be populated with a non-empty
 distinguished name matching the contents of the issuer field (Section
 5.1.2.3) 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 field.  A CA
 MAY issue more than one certificate with the same DN to the same
 subject entity.
 The subject 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).  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 the comparison rules in Section 7.1 to process
 unfamiliar attribute types (i.e., for name chaining) whose attribute
 values use one of the encoding options from DirectoryString.  Binary
 comparison should be used when unfamiliar attribute types include
 attribute values with encoding options other than those found in
 DirectoryString.  This allows implementations to process certificates
 with unfamiliar attributes in the subject name.
 When encoding attribute values of type DirectoryString, conforming
 CAs MUST use PrintableString or UTF8String encoding, with the
 following exceptions:
    (a)  When the subject of the certificate is a CA, the subject
         field MUST be encoded in the same way as it is encoded in the
         issuer field (Section 4.1.2.4) in all certificates issued by
         the subject CA.  Thus, if the subject CA encodes attributes
         in the issuer fields of certificates that it issues using the
         TeletexString, BMPString, or UniversalString encodings, then
         the subject field of certificates issued to that CA MUST use
         the same encoding.
    (b)  When the subject of the certificate is a CRL issuer, the
         subject field MUST be encoded in the same way as it is
         encoded in the issuer field (Section 5.1.2.3) in all CRLs
         issued by the subject CRL issuer.

Cooper, et al. Standards Track [Page 24] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (c)  TeletexString, BMPString, 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, including cases in which a new certificate is
         being issued to an existing subject or a certificate is being
         issued to a new subject where the attributes being encoded
         have been previously established in certificates issued to
         other subjects.  Certificate users SHOULD be prepared to
         receive certificates with these types.
 Legacy implementations exist where an electronic mail address is
 embedded in the subject distinguished name as an emailAddress
 attribute [RFC2985].  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., "subscriber@example.com" is the same as
 "SUBSCRIBER@EXAMPLE.COM").
 Conforming implementations generating new certificates with
 electronic mail addresses MUST use the rfc822Name in the subject
 alternative name extension (Section 4.2.1.6) 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 [RFC3279],
 [RFC4055], and [RFC4491].

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 MUST NOT generate
 certificates with unique identifiers.  Applications conforming to

Cooper, et al. Standards Track [Page 25] RFC 5280 PKIX Certificate and CRL Profile May 2008

 this profile SHOULD be capable of parsing certificates that include
 unique identifiers, but there are no processing requirements
 associated with the 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 are 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 relationships between CAs.  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 or a critical extension
 that contains information that it cannot process.  A non-critical
 extension MAY be ignored if it is not recognized, but MUST be
 processed if it is 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 that 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 DER 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 for CAs conforming to this
 profile.
 Conforming CAs MUST support key identifiers (Sections 4.2.1.1 and
 4.2.1.2), basic constraints (Section 4.2.1.9), key usage (Section
 4.2.1.3), and certificate policies (Section 4.2.1.4) extensions.  If
 the CA issues certificates with an empty sequence for the subject
 field, the CA MUST support the subject alternative name extension
 (Section 4.2.1.6).  Support for the remaining extensions is OPTIONAL.
 Conforming CAs MAY support extensions that are not identified within

Cooper, et al. Standards Track [Page 26] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 4.2.1.4), subject alternative name (Section
 4.2.1.6), basic constraints (Section 4.2.1.9), name constraints
 (Section 4.2.1.10), policy constraints (Section 4.2.1.11), extended
 key usage (Section 4.2.1.12), and inhibit anyPolicy (Section
 4.2.1.14).
 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 mappings (Section 4.2.1.5) 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 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

Cooper, et al. Standards Track [Page 27] RFC 5280 PKIX Certificate and CRL Profile May 2008

 that generates unique values.  Two common methods for generating key
 identifiers from the public key 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 or use of a similar method that uses a different hash
 algorithm.  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.
 Conforming CAs MUST mark this extension as non-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 4.2.1.9) where the
 value of cA is TRUE.  In conforming CA certificates, 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.  Applications
 are not required to verify that key identifiers match when performing
 certification path validation.
 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).

Cooper, et al. Standards Track [Page 28] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 bits).
 Other methods of generating unique numbers are also acceptable.
 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 or use of a similar method that uses a different hash
 algorithm.  Where a key identifier has been previously established,
 the CA SHOULD use the previously established identifier.
 Conforming CAs MUST mark this extension as non-critical.
 id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }
 SubjectKeyIdentifier ::= KeyIdentifier

4.2.1.3. Key Usage

 The key usage extension defines the purpose (e.g., encipherment,
 signature, certificate signing) of the key contained in the
 certificate.  The usage restriction might be employed when a 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.

Cooper, et al. Standards Track [Page 29] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Conforming CAs MUST include this extension in certificates that
 contain public keys that are used to validate digital signatures on
 other public key certificates or CRLs.  When present, conforming CAs
 SHOULD mark this extension as critical.
    id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }
    KeyUsage ::= BIT STRING {
         digitalSignature        (0),
         nonRepudiation          (1), -- recent editions of X.509 have
                              -- renamed this bit to contentCommitment
         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 for verifying digital signatures, other than signatures on
    certificates (bit 5) and CRLs (bit 6), such as those used in an
    entity authentication service, a data origin authentication
    service, and/or an integrity service.
    The nonRepudiation bit is asserted when the subject public key is
    used to verify digital signatures, other than signatures on
    certificates (bit 5) and CRLs (bit 6), used to provide a non-
    repudiation service that protects against the signing entity
    falsely denying some action.  In the case of later conflict, a
    reliable third party may determine the authenticity of the signed
    data.  (Note that recent editions of X.509 have renamed the
    nonRepudiation bit to contentCommitment.)
    The keyEncipherment bit is asserted when the subject public key is
    used for enciphering private or secret keys, i.e., for key
    transport.  For example, this bit shall be set when an RSA public
    key is to be used for encrypting a symmetric content-decryption
    key or an asymmetric private key.
    The dataEncipherment bit is asserted when the subject public key
    is used for directly enciphering raw user data without the use of
    an intermediate symmetric cipher.  Note that the use of this bit
    is extremely uncommon; almost all applications use key transport
    or key agreement to establish a symmetric key.

Cooper, et al. Standards Track [Page 30] RFC 5280 PKIX Certificate and CRL Profile May 2008

    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 signatures on public key certificates.  If the
    keyCertSign bit is asserted, then the cA bit in the basic
    constraints extension (Section 4.2.1.9) MUST also be asserted.
    The cRLSign bit is asserted when the subject public key is used
    for verifying signatures on certificate revocation lists (e.g.,
    CRLs, delta CRLs, or ARLs).
    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.
 If the keyUsage extension is present, then the subject public key
 MUST NOT be used to verify signatures on certificates or CRLs unless
 the corresponding keyCertSign or cRLSign bit is set.  If the subject
 public key is only to be used for verifying signatures on
 certificates and/or CRLs, then the digitalSignature and
 nonRepudiation bits SHOULD NOT be set.  However, the digitalSignature
 and/or nonRepudiation bits MAY be set in addition to the keyCertSign
 and/or cRLSign bits if the subject public key is to be used to verify
 signatures on certificates and/or CRLs as well as other objects.
 Combining the nonRepudiation bit in the keyUsage certificate
 extension with other keyUsage bits may have security implications
 depending on the context in which the certificate is to be used.
 Further distinctions between the digitalSignature and nonRepudiation
 bits may be provided in specific certificate policies.
 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 [RFC3279], [RFC4055], and [RFC4491].  When the
 keyUsage extension appears in a certificate, at least one of the bits
 MUST be set to 1.

Cooper, et al. Standards Track [Page 31] RFC 5280 PKIX Certificate and CRL Profile May 2008

4.2.1.4. 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.  A certificate policy OID MUST NOT appear more than once in a
 certificate policies extension.
 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 that include this certificate.  When a CA does
 not wish to limit the set of policies for certification paths that
 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 that 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 the 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.  Only those
 qualifiers returned as a result of path validation are considered.
 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.  Only user notices returned as a result of path
 validation are intended for display to the user.  If a notice is

Cooper, et al. Standards Track [Page 32] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.  Conforming CAs SHOULD NOT use the noticeRef
 option.
    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.  Conforming CAs SHOULD use the
    UTF8String encoding for explicitText, but MAY use IA5String.
    Conforming CAs MUST NOT encode explicitText as VisibleString or
    BMPString.  The explicitText string SHOULD NOT include any control
    characters (e.g., U+0000 to U+001F and U+007F to U+009F).  When
    the UTF8String encoding is used, all character sequences SHOULD be
    normalized according to Unicode normalization form C (NFC) [NFC].
 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.

Cooper, et al. Standards Track [Page 33] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 }
  1. - 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)) }

Cooper, et al. Standards Track [Page 34] RFC 5280 PKIX Certificate and CRL Profile May 2008

4.2.1.5. 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 mappings extension SHOULD
 also be asserted in a certificate policies extension in the same
 certificate.  Policies MUST NOT be mapped either to or from the
 special value anyPolicy (Section 4.2.1.4).
 In general, certificate policies that appear in the
 issuerDomainPolicy field of the policy mappings extension are not
 considered acceptable policies for inclusion in subsequent
 certificates in the certification path.  In some circumstances, a CA
 may wish to map from one policy (p1) to another (p2), but still wants
 the issuerDomainPolicy (p1) to be considered acceptable for inclusion
 in subsequent certificates.  This may occur, for example, if the CA
 is in the process of transitioning from the use of policy p1 to the
 use of policy p2 and has valid certificates that were issued under
 each of the policies.  A CA may indicate this by including two policy
 mappings in the CA certificates that it issues.  Each policy mapping
 would have an issuerDomainPolicy of p1; one policy mapping would have
 a subjectDomainPolicy of p1 and the other would have a
 subjectDomainPolicy of p2.
 This extension MAY be supported by CAs and/or applications.
 Conforming CAs SHOULD mark this extension as critical.
 id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }
 PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
      issuerDomainPolicy      CertPolicyId,
      subjectDomainPolicy     CertPolicyId }

4.2.1.6. Subject Alternative Name

 The subject alternative name extension allows identities to be bound
 to the subject of the certificate.  These identities may be included
 in addition to or in place of the identity in the subject field of
 the certificate.  Defined options include an Internet electronic mail

Cooper, et al. Standards Track [Page 35] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 also be
 represented in the subject field using the domainComponent attribute
 as described in Section 4.1.2.4.  Note that where such names are
 represented in the subject field implementations are not required to
 convert them into DNS names.
 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, then the issuing CA MUST include a
 subjectAltName extension that is marked as critical.  When including
 the subjectAltName extension in a certificate that has a non-empty
 subject distinguished name, conforming CAs SHOULD mark the
 subjectAltName extension as non-critical.
 When the subjectAltName extension contains an Internet mail address,
 the address MUST be stored in the rfc822Name.  The format of an
 rfc822Name is a "Mailbox" as defined in Section 4.1.2 of [RFC2821].
 A Mailbox has the form "Local-part@Domain".  Note that a Mailbox 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
 ">".  Rules for encoding Internet mail addresses that include
 internationalized domain names are specified in Section 7.5.
 When the subjectAltName extension contains an iPAddress, the address
 MUST be stored in the octet string in "network byte order", as
 specified in [RFC791].  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 [RFC791], the octet string MUST contain
 exactly four octets.  For IP version 6, as specified in
 [RFC2460], the octet string MUST contain exactly sixteen octets.
 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
 Section 3.5 of [RFC1034] and as modified by Section 2.1 of
 [RFC1123].  Note that while uppercase and lowercase letters are
 allowed in domain names, no significance is attached to the case.  In

Cooper, et al. Standards Track [Page 36] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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
 (subscriber.example.com instead of subscriber@example.com) MUST NOT
 be used; such identities are to be encoded as rfc822Name.  Rules for
 encoding internationalized domain names are specified in Section 7.2.
 When the subjectAltName extension contains a URI, the name MUST be
 stored in the uniformResourceIdentifier (an IA5String).  The name
 MUST NOT be a relative URI, and it MUST follow the URI syntax and
 encoding rules specified in [RFC3986].  The name MUST include both a
 scheme (e.g., "http" or "ftp") and a scheme-specific-part.  URIs that
 include an authority ([RFC3986], Section 3.2) MUST include a fully
 qualified domain name or IP address as the host.  Rules for encoding
 Internationalized Resource Identifiers (IRIs) are specified in
 Section 7.4.
 As specified in [RFC3986], the scheme name is not case-sensitive
 (e.g., "http" is equivalent to "HTTP").  The host part, if present,
 is also not case-sensitive, but other components of the scheme-
 specific-part may be case-sensitive.  Rules for comparing URIs are
 specified in Section 7.4.
 When the subjectAltName extension contains a DN in the directoryName,
 the encoding rules are the same as those specified for the issuer
 field in Section 4.1.2.4.  The DN MUST be unique for each subject
 entity certified by the one CA as defined by the issuer 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 [RFC4120] format names can be encoded into the otherName,
 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 4.2.1.10.
 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

Cooper, et al. Standards Track [Page 37] RFC 5280 PKIX Certificate and CRL Profile May 2008

 that encounter such a certificate when processing a certification
 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 }

4.2.1.7. Issuer Alternative Name

 As with Section 4.2.1.6, this extension is used to associate Internet
 style identities with the certificate issuer.  Issuer alternative
 name MUST be encoded as in 4.2.1.6.  Issuer alternative names are not
 processed as part of the certification path validation algorithm in
 Section 6.  (That is, issuer alternative names are not used in name
 chaining and name constraints are not enforced.)
 Where present, conforming CAs SHOULD mark this extension as non-
 critical.
 id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }
 IssuerAltName ::= GeneralNames

Cooper, et al. Standards Track [Page 38] RFC 5280 PKIX Certificate and CRL Profile May 2008

4.2.1.8. 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.
 Conforming CAs MUST mark this extension as non-critical.
 id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }
 SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

4.2.1.9. 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 may be used
 to verify certificate signatures.  If the cA boolean is not asserted,
 then the keyCertSign bit in the key usage extension MUST NOT be
 asserted.  If the basic constraints extension is not present in a
 version 3 certificate, or the extension is present but the cA boolean
 is not asserted, then the certified public key MUST NOT be used to
 verify certificate signatures.
 The pathLenConstraint field is meaningful only if the cA boolean is
 asserted and the key usage extension, if present, 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.  (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 no non-
 self-issued intermediate CA certificates 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.
 Conforming CAs MUST include this extension in all CA certificates
 that contain public keys used to validate digital signatures on
 certificates and MUST mark the extension as critical in such
 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

Cooper, et al. Standards Track [Page 39] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 }

4.2.1.10. 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 self-issued certificates (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.  Conforming CAs MUST mark this extension as
 critical and SHOULD NOT impose name constraints on the x400Address,
 ediPartyName, or registeredID name forms.  Conforming CAs MUST NOT
 issue certificates where name constraints is an empty sequence.  That
 is, either the permittedSubtrees field or the excludedSubtrees MUST
 be present.
 Applications conforming to this profile MUST be able to process name
 constraints that are imposed on the directoryName name form and
 SHOULD be able to process name constraints that are imposed on the
 rfc822Name, uniformResourceIdentifier, dNSName, and iPAddress name
 forms.  If a name constraints extension that is marked as critical
 imposes constraints on a particular name form, and an instance of
 that name form appears in the subject field or subjectAltName
 extension of a subsequent certificate, then the application MUST
 either process the constraint or reject the certificate.

Cooper, et al. Standards Track [Page 40] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Within this profile, the minimum and maximum fields are not used with
 any name forms, thus, the minimum MUST be zero, and maximum MUST be
 absent.  However, if an application encounters a critical name
 constraints extension that specifies other values for minimum or
 maximum for a name form that appears in a subsequent certificate, the
 application MUST either process these fields or reject the
 certificate.
 For URIs, the constraint applies to the host part of the name.  The
 constraint MUST be specified as a fully qualified domain name and MAY
 specify a host or a domain.  Examples would be "host.example.com" and
 ".example.com".  When the constraint begins with a period, it MAY be
 expanded with one or more labels.  That is, the constraint
 ".example.com" is satisfied by both host.example.com and
 my.host.example.com.  However, the constraint ".example.com" is not
 satisfied by "example.com".  When the constraint does not begin with
 a period, it specifies a host.  If a constraint is applied to the
 uniformResourceIdentifier name form and a subsequent certificate
 includes a subjectAltName extension with a uniformResourceIdentifier
 that does not include an authority component with a host name
 specified as a fully qualified domain name (e.g., if the URI either
 does not include an authority component or includes an authority
 component in which the host name is specified as an IP address), then
 the application MUST reject the certificate.
 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@example.com" indicates the root mailbox on the host
 "example.com".  To indicate all Internet mail addresses on a
 particular host, the constraint is specified as the host name.  For
 example, the constraint "example.com" is satisfied by any mail
 address at the host "example.com".  To specify any address within a
 domain, the constraint is specified with a leading period (as with
 URIs).  For example, ".example.com" indicates all the Internet mail
 addresses in the domain "example.com", but not Internet mail
 addresses on the host "example.com".
 DNS name restrictions are expressed as host.example.com.  Any DNS
 name that can be constructed by simply adding zero or more labels to
 the left-hand side of the name satisfies the name constraint.  For
 example, www.host.example.com would satisfy the constraint but
 host1.example.com would not.
 Legacy implementations exist where an electronic mail address is
 embedded in the subject distinguished name in an attribute of type
 emailAddress (Section 4.1.2.6).  When constraints are imposed on the

Cooper, et al. Standards Track [Page 41] RFC 5280 PKIX Certificate and CRL Profile May 2008

 rfc822Name name form, but the certificate does not include a subject
 alternative name, the rfc822Name 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 (when the certificate includes a non-empty
 subject field) and to any names of type directoryName in the
 subjectAltName extension.  Restrictions of the form x400Address MUST
 be applied to any names of type x400Address in the subjectAltName
 extension.
 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 7.1.  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 4.2.1.6 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 4632 (CIDR) to represent an
 address range [RFC4632].  For IPv6 addresses, the iPAddress field
 MUST contain 32 octets similarly encoded.  For example, a name
 constraint for "class C" subnet 192.0.2.0 is represented as the
 octets C0 00 02 00 FF FF FF 00, representing the CIDR notation
 192.0.2.0/24 (mask 255.255.255.0).
 Additional rules for encoding and processing name constraints are
 specified in Section 7.
 The syntax and semantics for name constraints for otherName,
 ediPartyName, and registeredID are not defined by this specification,
 however, syntax and semantics for name constraints for other name
 forms may be specified in other documents.
    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

Cooper, et al. Standards Track [Page 42] RFC 5280 PKIX Certificate and CRL Profile May 2008

    GeneralSubtree ::= SEQUENCE {
         base                    GeneralName,
         minimum         [0]     BaseDistance DEFAULT 0,
         maximum         [1]     BaseDistance OPTIONAL }
    BaseDistance ::= INTEGER (0..MAX)

4.2.1.11. 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
 that has been declared equivalent through policy mapping.
 Conforming applications MUST be able to process the
 requireExplicitPolicy field and SHOULD be able to process the
 inhibitPolicyMapping field.  Applications that support the
 inhibitPolicyMapping field MUST also implement support for the
 policyMappings extension.  If the policyConstraints extension is
 marked as critical and the inhibitPolicyMapping field is present,
 applications that do not implement support for the
 inhibitPolicyMapping field MUST reject the certificate.
 Conforming CAs MUST NOT issue certificates where policy constraints
 is an empty sequence.  That is, either the inhibitPolicyMapping field
 or the requireExplicitPolicy field MUST be present.  The behavior of
 clients that encounter an empty policy constraints field is not
 addressed in this profile.
 Conforming CAs MUST mark this extension as critical.

Cooper, et al. Standards Track [Page 43] RFC 5280 PKIX Certificate and CRL Profile May 2008

 id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }
 PolicyConstraints ::= SEQUENCE {
      requireExplicitPolicy           [0] SkipCerts OPTIONAL,
      inhibitPolicyMapping            [1] SkipCerts OPTIONAL }
 SkipCerts ::= INTEGER (0..MAX)

4.2.1.12. 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 the extended key usage extension be
 present and 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 in addition to the
 particular key purposes required by the applications.  Conforming CAs
 SHOULD NOT mark this extension as critical if the anyExtendedKeyUsage
 KeyPurposeId is present.  Applications that require the presence of a
 particular purpose MAY reject certificates that include the
 anyExtendedKeyUsage OID but not the particular OID expected for the
 application.

Cooper, et al. Standards Track [Page 44] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 }
 -- Email 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

4.2.1.13. 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.

Cooper, et al. Standards Track [Page 45] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 conforming CAs MUST omit the cRLIssuer field and MUST include
 the distributionPoint field.
 When the distributionPoint field is present, it contains either a
 SEQUENCE of general names or a single value, nameRelativeToCRLIssuer.
 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 distributionPoint field contains a directoryName, the entry
 for that directoryName contains the current CRL for the associated
 reasons and the CRL is issued by the associated cRLIssuer.  The CRL
 may be stored in either the certificateRevocationList or
 authorityRevocationList attribute.  The CRL is to be obtained by the
 application from whatever directory server is locally configured.
 The protocol the application uses to access the directory (e.g., DAP
 or LDAP) is a local matter.
 If the DistributionPointName 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.  When the HTTP or FTP URI scheme is used, the
 URI MUST point to a single DER encoded CRL as specified in
 [RFC2585].  HTTP server implementations accessed via the URI SHOULD
 specify the media type application/pkix-crl in the content-type
 header field of the response.  When the LDAP URI scheme [RFC4516] is
 used, the URI MUST include a <dn> field containing the distinguished
 name of the entry holding the CRL, MUST include a single <attrdesc>
 that contains an appropriate attribute description for the attribute
 that holds the CRL [RFC4523], and SHOULD include a <host>
 (e.g., <ldap://ldap.example.com/cn=example%20CA,dc=example,dc=com?
 certificateRevocationList;binary>).  Omitting the <host> (e.g.,
 <ldap:///cn=CA,dc=example,dc=com?authorityRevocationList;binary>) has
 the effect of relying on whatever a priori knowledge the client might
 have to contact an appropriate server.  When present,
 DistributionPointName SHOULD include at least one LDAP or HTTP URI.
 If the DistributionPointName contains the single value
 nameRelativeToCRLIssuer, the value provides a distinguished name

Cooper, et al. Standards Track [Page 46] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.  Conforming CAs SHOULD NOT use
 nameRelativeToCRLIssuer to specify distribution point names.  The
 DistributionPointName MUST NOT use the nameRelativeToCRLIssuer
 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.  This profile
 RECOMMENDS against segmenting CRLs by reason code.  When a conforming
 CA includes a cRLDistributionPoints extension in a certificate, it
 MUST include at least one DistributionPoint that points to a CRL that
 covers the certificate for all reasons.
 The cRLIssuer identifies the entity that signs and issues the CRL.
 If present, the cRLIssuer MUST only contain the distinguished name
 (DN) from the issuer field of the CRL to which the DistributionPoint
 is pointing.  The encoding of the name in the cRLIssuer field MUST be
 exactly the same as the encoding in issuer field of the CRL.  If the
 cRLIssuer field is included and the DN in that field does not
 correspond to an X.500 or LDAP directory entry where CRL is located,
 then conforming CAs MUST include the distributionPoint field.
 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 }

Cooper, et al. Standards Track [Page 47] RFC 5280 PKIX Certificate and CRL Profile May 2008

 ReasonFlags ::= BIT STRING {
      unused                  (0),
      keyCompromise           (1),
      cACompromise            (2),
      affiliationChanged      (3),
      superseded              (4),
      cessationOfOperation    (5),
      certificateHold         (6),
      privilegeWithdrawn      (7),
      aACompromise            (8) }

4.2.1.14. Inhibit anyPolicy

 The inhibit anyPolicy extension can be used in certificates issued to
 CAs.  The inhibit anyPolicy extension indicates that the special
 anyPolicy OID, with the value { 2 5 29 32 0 }, is not considered an
 explicit match for other certificate policies except when it appears
 in an intermediate self-issued CA certificate.  The value indicates
 the number of additional non-self-issued 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.
 Conforming CAs MUST mark this extension as critical.
 id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }
 InhibitAnyPolicy ::= SkipCerts
 SkipCerts ::= INTEGER (0..MAX)

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

 The freshest CRL extension identifies how delta CRL information is
 obtained.  The extension MUST be marked as non-critical by conforming
 CAs.  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
 4.2.1.13.  The same conventions apply to both extensions.
 id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }
 FreshestCRL ::= CRLDistributionPoints

Cooper, et al. Standards Track [Page 48] RFC 5280 PKIX Certificate and CRL Profile May 2008

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 issuer or the subject.
 Each extension contains a sequence of access methods and access
 locations.  The access method is an object identifier that indicates
 the type of information that is available.  The access location is a
 GeneralName that implicitly specifies the location and format of the
 information and the method for obtaining the information.
 Object identifiers are defined for the private extensions.  The
 object identifiers associated with the private extensions are 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
 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.  Conforming CAs MUST mark this
 extension as 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 }

Cooper, et al. Standards Track [Page 49] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Each entry in the sequence AuthorityInfoAccessSyntax describes the
 format and location of additional information provided by the issuer
 of the certificate in which this extension appears.  The type and
 format of the information are 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.
 In a public key certificate, the id-ad-caIssuers OID is used when the
 additional information lists certificates that were issued 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.
 When the accessLocation is a directoryName, the information is to be
 obtained by the application from whatever directory server is locally
 configured.  The entry for the directoryName contains CA certificates
 in the crossCertificatePair and/or cACertificate attributes as
 specified in [RFC4523].  The protocol that application uses to access
 the directory (e.g., DAP or LDAP) is a local matter.
 Where the information is available via LDAP, the accessLocation
 SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
 include a <dn> field containing the distinguished name of the entry
 holding the certificates, MUST include an <attributes> field that
 lists appropriate attribute descriptions for the attributes that hold
 the DER encoded certificates or cross-certificate pairs [RFC4523],
 and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
 dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).
 Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
 cACertificate;binary>) has the effect of relying on whatever a priori
 knowledge the client might have to contact an appropriate server.
 Where the information is available via HTTP or FTP, accessLocation
 MUST be a uniformResourceIdentifier and the URI MUST point to either
 a single DER encoded certificate as specified in [RFC2585] or a
 collection of certificates in a BER or DER encoded "certs-only" CMS
 message as specified in [RFC2797].

Cooper, et al. Standards Track [Page 50] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Conforming applications that support HTTP or FTP for accessing
 certificates MUST be able to accept individual DER encoded
 certificates and SHOULD be able to accept "certs-only" CMS messages.
 HTTP server implementations accessed via the URI SHOULD specify the
 media type application/pkix-cert [RFC2585] in the content-type header
 field of the response for a single DER encoded certificate and SHOULD
 specify the media type application/pkcs7-mime [RFC2797] in the
 content-type header field of the response for "certs-only" CMS
 messages.  For FTP, the name of a file that contains a single DER
 encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
 name of a file that contains a "certs-only" CMS message SHOULD have a
 suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
 or file extension as a hint to the content, but should not depend
 solely on the presence of the correct media type or file extension in
 the server response.
 The semantics of other id-ad-caIssuers accessLocation name forms are
 not defined.
 An authorityInfoAccess extension may include multiple instances of
 the id-ad-caIssuers accessMethod.  The different instances may
 specify different methods for accessing the same information or may
 point to different information.  When the id-ad-caIssuers
 accessMethod is used, at least one instance SHOULD specify an
 accessLocation that is an HTTP [RFC2616] or LDAP [RFC4516] URI.
 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) [RFC2560].
 When id-ad-ocsp appears as accessMethod, the accessLocation field is
 the location of the OCSP responder, using the conventions defined in
 [RFC2560].
 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

Cooper, et al. Standards Track [Page 51] RFC 5280 PKIX Certificate and CRL Profile May 2008

 specifications for the supported services.  This extension may be
 included in end entity or CA certificates.  Conforming CAs MUST mark
 this extension as 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 are 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 that
 publishes certificates it issues in a repository.  The accessLocation
 field is defined as a GeneralName, which can take several forms.
 When the accessLocation is a directoryName, the information is to be
 obtained by the application from whatever directory server is locally
 configured.  When the extension is used to point to CA certificates,
 the entry for the directoryName contains CA certificates in the
 crossCertificatePair and/or cACertificate attributes as specified in
 [RFC4523].  The protocol the application uses to access the directory
 (e.g., DAP or LDAP) is a local matter.
 Where the information is available via LDAP, the accessLocation
 SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
 include a <dn> field containing the distinguished name of the entry
 holding the certificates, MUST include an <attributes> field that
 lists appropriate attribute descriptions for the attributes that hold
 the DER encoded certificates or cross-certificate pairs [RFC4523],
 and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
 dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).

Cooper, et al. Standards Track [Page 52] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
 cACertificate;binary>) has the effect of relying on whatever a priori
 knowledge the client might have to contact an appropriate server.
 Where the information is available via HTTP or FTP, accessLocation
 MUST be a uniformResourceIdentifier and the URI MUST point to either
 a single DER encoded certificate as specified in [RFC2585] or a
 collection of certificates in a BER or DER encoded "certs-only" CMS
 message as specified in [RFC2797].
 Conforming applications that support HTTP or FTP for accessing
 certificates MUST be able to accept individual DER encoded
 certificates and SHOULD be able to accept "certs-only" CMS messages.
 HTTP server implementations accessed via the URI SHOULD specify the
 media type application/pkix-cert [RFC2585] in the content-type header
 field of the response for a single DER encoded certificate and SHOULD
 specify the media type application/pkcs7-mime [RFC2797] in the
 content-type header field of the response for "certs-only" CMS
 messages.  For FTP, the name of a file that contains a single DER
 encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
 name of a file that contains a "certs-only" CMS message SHOULD have a
 suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
 or file extension as a hint to the content, but should not depend
 solely on the presence of the correct media type or file extension in
 the server response.
 The semantics of other id-ad-caRepository accessLocation name forms
 are not defined.
 A subjectInfoAccess extension may include multiple instances of the
 id-ad-caRepository accessMethod.  The different instances may specify
 different methods for accessing the same information or may point to
 different information.  When the id-ad-caRepository accessMethod is
 used, at least one instance SHOULD specify an accessLocation that is
 an HTTP [RFC2616] or LDAP [RFC4516] URI.
 The id-ad-timeStamping OID is used when the subject offers
 timestamping services using the Time Stamp Protocol defined in
 [RFC3161].  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.

Cooper, et al. Standards Track [Page 53] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.  The CRL issuer is either the CA or an entity
 that has been authorized by the CA to issue CRLs.  CAs publish CRLs
 to provide status information about the certificates they issued.
 However, a CA may delegate this responsibility to another trusted
 authority.
 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 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.  A full and complete CRL lists all unexpired
 certificates issued by a CA that have been revoked for any reason.
 (Note that since CAs and CRL issuers are identified by name, the
 scope of a CRL is not affected by the key used to sign the CRL or the
 key(s) used to sign certificates.)

Cooper, et al. Standards Track [Page 54] RFC 5280 PKIX Certificate and CRL Profile May 2008

 If the scope of the CRL includes one or more certificates issued by
 an entity other than the CRL issuer, then it is an indirect CRL.  The
 scope of an indirect CRL may be limited to certificates issued by a
 single CA or may include certificates issued by multiple CAs.  If the
 issuer of the indirect CRL is a CA, then the scope of the indirect
 CRL MAY also include certificates issued by the issuer of the CRL.
 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 defines one private Internet CRL extension but does not
 define any private 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.

Cooper, et al. Standards Track [Page 55] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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, version MUST be v2
                                }  OPTIONAL,
      crlExtensions           [0]  EXPLICIT Extensions OPTIONAL
                                    -- if present, version MUST be v2
                                }
  1. - Version, Time, CertificateSerialNumber, and Extensions
  2. - are all defined in the ASN.1 in Section 4.1
  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.

Cooper, et al. Standards Track [Page 56] RFC 5280 PKIX Certificate and CRL Profile May 2008

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.  [RFC3279], [RFC4055], and [RFC4491] list 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 [RFC3279], [RFC4055], and [RFC4491].
 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.

Cooper, et al. Standards Track [Page 57] RFC 5280 PKIX Certificate and CRL Profile May 2008

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, and the date and time the
 CRL was issued.
 Optional fields include the date and time by which the CRL issuer
 will issue the next CRL, 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.  This profile requires conforming CRL issuers to include
 the nextUpdate field and 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.  [RFC3279], [RFC4055], and [RFC4491] list 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 that has signed and issued the
 CRL.  The issuer identity is carried in the issuer field.
 Alternative name forms may also appear in the issuerAltName extension
 (Section 5.2.2).  The issuer field MUST contain a non-empty X.500
 distinguished name (DN).  The issuer 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

Cooper, et al. Standards Track [Page 58] RFC 5280 PKIX Certificate and CRL Profile May 2008

 this profile MUST encode thisUpdate as GeneralizedTime for dates in
 the year 2050 or later.  Conforming applications MUST be able to
 process dates that are encoded in either UTCTime or GeneralizedTime.
 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.
 Conforming CRL issuers MUST include the nextUpdate field in all CRLs.
 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 that 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.  Conforming applications MUST be able to
 process dates that are encoded in either UTCTime or GeneralizedTime.
 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.

Cooper, et al. Standards Track [Page 59] RFC 5280 PKIX Certificate and CRL Profile May 2008

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.  If a CRL contains a critical extension
 that the application cannot process, then the application MUST NOT
 use that CRL to determine the status of certificates.  However,
 applications may ignore unrecognized non-critical extensions.  The
 following subsections present those extensions used within Internet
 CRLs.  Communities may elect to include extensions in CRLs that are
 not defined in this specification.  However, caution should be
 exercised in adopting any critical extensions in CRLs that 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 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 name extension allows additional identities to
 be associated with the issuer of the CRL.  Defined options include an
 electronic mail address (rfc822Name), a DNS name, an IP address, and
 a URI.  Multiple instances of a name form and multiple name forms may

Cooper, et al. Standards Track [Page 60] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.
 Conforming CRL issuers SHOULD mark the issuerAltName extension as
 non-critical.
 The OID and syntax for this CRL extension are defined in Section
 4.2.1.7.

5.2.3. CRL Number

 The CRL number is a non-critical CRL extension that 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 and MUST mark this extension as non-critical.
 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.  Conforming CRL issuers MUST NOT use CRLNumber
 values longer than 20 octets.
 id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }
 CRLNumber ::= INTEGER (0..MAX)

Cooper, et al. Standards Track [Page 61] RFC 5280 PKIX Certificate and CRL Profile May 2008

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 that 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

Cooper, et al. Standards Track [Page 62] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.

Cooper, et al. Standards Track [Page 63] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 (for any revocation reason, including certificateHold), if it
 is 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 the time 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.

Cooper, et al. Standards Track [Page 64] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.  However, implementations that do not support this
 extension MUST either treat the status of any certificate not listed
 on this CRL as unknown or locate another CRL that does not contain
 any unrecognized critical extensions.
 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
 from 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 a CRL includes an issuingDistributionPoint extension with
 onlySomeReasons present, then every certificate in the scope of the
 CRL that is revoked MUST be assigned a revocation reason other than
 unspecified.  The assigned revocation reason is used to determine on
 which CRL(s) to list the revoked certificate, however, there is no
 requirement to include the reasonCode CRL entry extension in the
 corresponding CRL entry.
 The syntax and semantics for the distributionPoint field are the same
 as for the distributionPoint field in the cRLDistributionPoints
 extension (Section 4.2.1.13).  If the distributionPoint field is
 present, then it MUST include at least one of names from the
 corresponding distributionPoint field of the cRLDistributionPoints

Cooper, et al. Standards Track [Page 65] RFC 5280 PKIX Certificate and CRL Profile May 2008

 extension of every certificate that is within the scope of this CRL.
 The identical encoding MUST be used in the distributionPoint fields
 of the certificate and the CRL.
 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.
 If the scope of the CRL only includes certificates issued by the CRL
 issuer, then the indirectCRL boolean MUST be set to FALSE.
 Otherwise, if the scope of the CRL includes certificates issued by
 one or more authorities other than the CRL issuer, the indirectCRL
 boolean MUST be set to TRUE.  The authority responsible for each
 entry is indicated by the certificate issuer CRL entry extension
 (Section 5.3.3).
 If the scope of the CRL only includes end entity public key
 certificates, then onlyContainsUserCerts MUST be set to TRUE.  If the
 scope of the CRL only includes CA certificates, then
 onlyContainsCACerts MUST be set to TRUE.  If either
 onlyContainsUserCerts or onlyContainsCACerts is set to TRUE, then the
 scope of the CRL MUST NOT include any version 1 or version 2
 certificates.  Conforming CRLs issuers MUST set the
 onlyContainsAttributeCerts boolean to FALSE.
 Conforming CRLs issuers MUST NOT issue CRLs where the DER encoding of
 the issuing distribution point extension is an empty sequence.  That
 is, if onlyContainsUserCerts, onlyContainsCACerts, indirectCRL, and
 onlyContainsAttributeCerts are all FALSE, then either the
 distributionPoint field or the onlySomeReasons field MUST be present.
 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 }
  1. - at most one of onlyContainsUserCerts, onlyContainsCACerts,
  2. - and onlyContainsAttributeCerts may be set to TRUE.

Cooper, et al. Standards Track [Page 66] RFC 5280 PKIX Certificate and CRL Profile May 2008

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.  Conforming CRL issuers MUST mark this
 extension as 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 4.2.1.13.  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 4.2.1.13 apply to this extension.
 id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }
 FreshestCRL ::= CRLDistributionPoints

5.2.7. Authority Information Access

 This section defines the use of the Authority Information Access
 extension in a CRL.  The syntax and semantics defined in Section
 4.2.2.1 for the certificate extension are also used for the CRL
 extension.
 This CRL extension MUST be marked as non-critical.
 When present in a CRL, this extension MUST include at least one
 AccessDescription specifying id-ad-caIssuers as the accessMethod.
 The id-ad-caIssuers OID is used when the information available lists
 certificates that can be used to verify the signature on the CRL
 (i.e., certificates that have a subject name that matches the issuer
 name on the CRL and that have a subject public key that corresponds
 to the private key used to sign the CRL).  Access method types other
 than id-ad-caIssuers MUST NOT be included.  At least one instance of
 AccessDescription SHOULD specify an accessLocation that is an HTTP
 [RFC2616] or LDAP [RFC4516] URI.

Cooper, et al. Standards Track [Page 67] RFC 5280 PKIX Certificate and CRL Profile May 2008

 Where the information is available via HTTP or FTP, accessLocation
 MUST be a uniformResourceIdentifier and the URI MUST point to either
 a single DER encoded certificate as specified in [RFC2585] or a
 collection of certificates in a BER or DER encoded "certs-only" CMS
 message as specified in [RFC2797].
 Conforming applications that support HTTP or FTP for accessing
 certificates MUST be able to accept individual DER encoded
 certificates and SHOULD be able to accept "certs-only" CMS messages.
 HTTP server implementations accessed via the URI SHOULD specify the
 media type application/pkix-cert [RFC2585] in the content-type header
 field of the response for a single DER encoded certificate and SHOULD
 specify the media type application/pkcs7-mime [RFC2797] in the
 content-type header field of the response for "certs-only" CMS
 messages.  For FTP, the name of a file that contains a single DER
 encoded certificate SHOULD have a suffix of ".cer" [RFC2585] and the
 name of a file that contains a "certs-only" CMS message SHOULD have a
 suffix of ".p7c" [RFC2797].  Consuming clients may use the media type
 or file extension as a hint to the content, but should not depend
 solely on the presence of the correct media type or file extension in
 the server response.
 When the accessLocation is a directoryName, the information is to be
 obtained by the application from whatever directory server is locally
 configured.  When one CA public key is used to validate signatures on
 certificates and CRLs, the desired CA certificate is stored in the
 crossCertificatePair and/or cACertificate attributes as specified in
 [RFC4523].  When different public keys are used to validate
 signatures on certificates and CRLs, the desired certificate is
 stored in the userCertificate attribute as specified in [RFC4523].
 Thus, implementations that support the directoryName form of
 accessLocation MUST be prepared to find the needed certificate in any
 of these three attributes.  The protocol that an application uses to
 access the directory (e.g., DAP or LDAP) is a local matter.
 Where the information is available via LDAP, the accessLocation
 SHOULD be a uniformResourceIdentifier.  The LDAP URI [RFC4516] MUST
 include a <dn> field containing the distinguished name of the entry
 holding the certificates, MUST include an <attributes> field that
 lists appropriate attribute descriptions for the attributes that hold
 the DER encoded certificates or cross-certificate pairs [RFC4523],
 and SHOULD include a <host> (e.g., <ldap://ldap.example.com/cn=CA,
 dc=example,dc=com?cACertificate;binary,crossCertificatePair;binary>).
 Omitting the <host> (e.g., <ldap:///cn=exampleCA,dc=example,dc=com?
 cACertificate;binary>) has the effect of relying on whatever a priori
 knowledge the client might have to contact an appropriate server.

Cooper, et al. Standards Track [Page 68] RFC 5280 PKIX Certificate and CRL Profile May 2008

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.  If a CRL
 contains a critical CRL entry extension that the application cannot
 process, then the application MUST NOT use that CRL to determine the
 status of any certificates.  However, applications may ignore
 unrecognized non-critical CRL entry extensions.
 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 CRL
 entry extensions in CRLs that might be used in a general context.
 Support for the CRL entry extensions defined in this specification is
 optional for conforming CRL issuers and applications.  However, CRL
 issuers SHOULD include reason codes (Section 5.3.1) and invalidity
 dates (Section 5.3.2) 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.
 The removeFromCRL (8) reasonCode value may only appear in delta CRLs
 and indicates that a certificate is to be removed from a CRL because
 either the certificate expired or was removed from hold.  All other
 reason codes may appear in any CRL and indicate that the specified
 certificate should be considered revoked.

Cooper, et al. Standards Track [Page 69] RFC 5280 PKIX Certificate and CRL Profile May 2008

 id-ce-cRLReasons OBJECT IDENTIFIER ::= { id-ce 21 }
  1. - reasonCode ::= { CRLReason }
 CRLReason ::= ENUMERATED {
      unspecified             (0),
      keyCompromise           (1),
      cACompromise            (2),
      affiliationChanged      (3),
      superseded              (4),
      cessationOfOperation    (5),
      certificateHold         (6),
           -- value 7 is not used
      removeFromCRL           (8),
      privilegeWithdrawn      (9),
      aACompromise           (10) }

5.3.2. 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

5.3.3. 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.  When present, the certificate issuer CRL entry extension
 includes one or more names from the issuer field and/or issuer
 alternative name extension of the certificate that corresponds to the
 CRL entry.  If this extension is not present on the first entry in an
 indirect CRL, the certificate issuer defaults to the CRL issuer.  On

Cooper, et al. Standards Track [Page 70] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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
 Conforming CRL issuers MUST include in this extension the
 distinguished name (DN) from the issuer field of the certificate that
 corresponds to this CRL entry.  The encoding of the DN MUST be
 identical to the encoding used in the certificate.
 CRL issuers MUST mark this extension as critical since an
 implementation that ignored this extension 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 that are specified in the
 certificates that comprise the path and inputs that 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 that 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

Cooper, et al. Standards Track [Page 71] RFC 5280 PKIX Certificate and CRL Profile May 2008

 validation procedure is the same regardless of the choice of trust
 anchor.  In addition, different applications may rely on different
 trust anchors, or may accept paths that begin with any of a set of
 trust anchors.
 Section 6.2 describes methods for using the path validation algorithm
 in specific implementations.
 Section 6.3 describes the steps necessary to determine if a
 certificate is revoked 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
 conforming 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 mappings
 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.
 While the certificate and CRL profiles specified in Sections 4 and 5
 of this document specify values for certificate and CRL fields and
 extensions that are considered to be appropriate for the Internet
 PKI, the algorithm presented in this section is not limited to
 accepting certificates and CRLs that conform to these profiles.
 Therefore, the algorithm only includes checks to verify that the
 certification path is valid according to X.509 and does not include
 checks to verify that the certificates and CRLs conform to this
 profile.  While the algorithm could be extended to include checks for
 conformance to the profiles in Sections 4 and 5, this profile
 RECOMMENDS against including such checks.
 The algorithm presented in this section validates the certificate
 with respect to the current date and time.  A conforming
 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.

Cooper, et al. Standards Track [Page 72] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 target certificate, based
 on the public key of the trust anchor.  In most cases, the target
 certificate will be an end entity certificate, but the target
 certificate may be a CA certificate as long as the subject public key
 is to be used for a purpose other than verifying the signature on a
 public key certificate.  Verifying the binding between the name and
 subject public key 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 (i.e., the
         target certificate); and
    (d)  for all x in {1, ..., n}, the certificate was valid at the
         time in question.
 A certificate MUST NOT appear more than once in a prospective
 certification path.
 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
 is 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 mappings extension, policy constraints extension,
 and inhibit anyPolicy extension.  To achieve this, the path

Cooper, et al. Standards Track [Page 73] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 same DN appears in the subject
 and issuer fields (the two DNs are the same if they match according
 to the rules specified in Section 7.1).  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.

Cooper, et al. Standards Track [Page 74] RFC 5280 PKIX Certificate and CRL Profile May 2008

                         +-------+
                         | 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 that the following nine inputs are provided to
 the path processing logic:
    (a)  a prospective certification path of length n.
    (b)  the current date/time.

Cooper, et al. Standards Track [Page 75] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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.
    When the trust anchor information is provided in the form of a
    certificate, the name in the subject field is used as the trusted
    issuer name and the contents of the subjectPublicKeyInfo field is
    used as the source of the trusted public key algorithm and the
    trusted public key.  The trust 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.
    (h)  initial-permitted-subtrees, which indicates for each name
         type (e.g., X.500 distinguished names, email addresses, or IP
         addresses) a set of subtrees within which all subject names
         in every certificate in the certification path MUST fall.
         The initial-permitted-subtrees input includes a set for each
         name type.  For each name type, the set may consist of a

Cooper, et al. Standards Track [Page 76] RFC 5280 PKIX Certificate and CRL Profile May 2008

         single subtree that includes all names of that name type or
         one or more subtrees that each specifies a subset of the
         names of that name type, or the set may be empty.  If the set
         for a name type is empty, then the certification path will be
         considered invalid if any certificate in the certification
         path includes a name of that name type.
    (i)  initial-excluded-subtrees, which indicates for each name type
         (e.g., X.500 distinguished names, email addresses, or IP
         addresses) a set of subtrees within which no subject name in
         any certificate in the certification path may fall.  The
         initial-excluded-subtrees input includes a set for each name
         type.  For each name type, the set may be empty or may
         consist of one or more subtrees that each specifies a subset
         of the names of that name type.  If the set for a name type
         is empty, then no names of that name type are excluded.
 Conforming implementations are not required to support the setting of
 all of these inputs.  For example, a conforming implementation may be
 designed to validate all certification paths using a value of FALSE
 for initial-any-policy-inhibit.

6.1.2. Initialization

 This initialization phase establishes eleven state variables based
 upon the nine 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 three data
         objects: the valid policy, a set of associated policy
         qualifiers, and a set of one or more expected policy values.
         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.

Cooper, et al. Standards Track [Page 77] RFC 5280 PKIX Certificate and CRL Profile May 2008

       (2)  The qualifier_set is a set of policy qualifiers associated
            with the valid policy in certificate x.
       (3)  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, and an
    expected_policy_set with the single value anyPolicy.  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
            +----------------+
            |  {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, and the initial value is initial-permitted-subtrees.
    (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 is initial-excluded-subtrees.
    (d)  explicit_policy:  an integer that 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 cannot remove this
         requirement.  If initial-explicit-policy is set, then the
         initial value is 0, otherwise the initial value is n+1.

Cooper, et al. Standards Track [Page 78] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (e)  inhibit_anyPolicy:  an integer that 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 other than an intermediate self-issued
         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 cannot 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 that 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 that policy mapping is not permitted, it cannot 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 name
         provided in the trust anchor information.

Cooper, et al. Standards Track [Page 79] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 signature on the certificate can be verified using
            working_public_key_algorithm, 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.  This
            may be determined by obtaining the appropriate CRL
            (Section 6.3), by 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 any 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 any of the excluded_subtrees for that name type.

Cooper, et al. Standards Track [Page 80] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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
            for policy P and P-Q denote the qualifier set for policy
            P.  Perform the following steps in order:
          (i)   For each node of depth i-1 in the valid_policy_tree
                where P-OID is in the expected_policy_set, create a
                child node as follows: 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 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
                           |  {Gold, White}  |
                           +-----------------+
                                    |
                                    |
                                    |
                                    V
                           +-----------------+
                           |      Gold       |
                           +-----------------+
                           |       {}        |
                           +-----------------+   node of depth i
                           |     {Gold}      |
                           +-----------------+
                  Figure 4.  Processing an Exact Match

Cooper, et al. Standards Track [Page 81] RFC 5280 PKIX Certificate and CRL Profile May 2008

          (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
                                 |   {anyPolicy}   |
                                 +-----------------+
                                    /           \
                                   /             \
                                  /               \
                                 /                 \
                   +-----------------+          +-----------------+
                   |      Gold       |          |     Silver      |
                   +-----------------+          +-----------------+
                   |       {}        |          |   {Q-Silver}    |
                   +-----------------+ nodes of +-----------------+
                   |     {Gold}      | depth i  |    {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_anyPolicy 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

Cooper, et al. Standards Track [Page 82] RFC 5280 PKIX Certificate and CRL Profile May 2008

            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 with no policy qualifiers, but
            Gold and Silver do not appear.  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
                             |  {Gold, Silver} |
                             +-----------------+
                                /           \
                               /             \
                              /               \
                             /                 \
               +-----------------+          +-----------------+
               |      Gold       |          |     Silver      |
               +-----------------+          +-----------------+
               |       {}        |          |       {}        |
               +-----------------+ nodes of +-----------------+
               |     {Gold}      | depth i  |    {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 they are deleted.
            Applying this rule to the resulting tree will cause the
            node at depth i-2 that is marked with a 'Y' to be deleted.
            In the resulting tree, there are no nodes of depth i-1 or
            less without children, and this step is complete.

Cooper, et al. Standards Track [Page 83] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 Section 6.1.4.  If i is equal to n, perform the wrap-up
 steps listed in Section 6.1.5.
                               +-----------+
                               |           | 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

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 mappings extension is present, verify that the
         special value anyPolicy does not appear as an
         issuerDomainPolicy or a subjectDomainPolicy.
    (b)  If a policy mappings extension is present, then for each
         issuerDomainPolicy ID-P in the policy mappings extension:

Cooper, et al. Standards Track [Page 84] RFC 5280 PKIX Certificate and CRL Profile May 2008

       (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 mappings 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; and
          (iii)  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.

Cooper, et al. Standards Track [Page 85] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 example.com and foo.example.com is
            foo.example.com.  And the intersection of example.com and
            example.net 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 example.com and foo.example.com is
            example.com.  And the union of example.com and example.net
            is both name spaces.
    (h)  If certificate i is not self-issued:
       (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_anyPolicy is not 0, decrement inhibit_anyPolicy
            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.

Cooper, et al. Standards Track [Page 86] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (j)  If the inhibitAnyPolicy extension is included in the
         certificate and is less than inhibit_anyPolicy, set
         inhibit_anyPolicy to the value of inhibitAnyPolicy.
    (k)  If certificate i is a version 3 certificate, verify that the
         basicConstraints extension is present and that cA is set to
         TRUE.  (If certificate i is a version 1 or version 2
         certificate, then the application MUST either verify that
         certificate i is a CA certificate through out-of-band means
         or reject the certificate.  Conforming implementations may
         choose to reject all version 1 and version 2 intermediate
         certificates.)
    (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 pathLenConstraint is present in the certificate and is
         less than max_path_length, set max_path_length to the value
         of pathLenConstraint.
    (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 that is relevant to path
         processing.
 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 Section
 6.1.3.

6.1.5. Wrap-Up Procedure

 To complete the processing of the target certificate, perform the
 following steps for certificate n:
    (a)  If 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.

Cooper, et al. Standards Track [Page 87] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 that is relevant to path
         processing.
    (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.

Cooper, et al. Standards Track [Page 88] RFC 5280 PKIX Certificate and CRL Profile May 2008

           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, 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.  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

Cooper, et al. Standards Track [Page 89] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.
 An implementation MAY augment the algorithm presented in Section 6.1
 to further limit the set of valid certification paths that begin with
 a particular trust anchor.  For example, an implementation MAY modify
 the algorithm to apply a path length constraint to a specific trust
 anchor during the initialization phase, or the application MAY
 require the presence of a particular alternative name form in the
 target 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.
 Where a CA distributes self-signed certificates to specify trust
 anchor information, certificate extensions can be used to specify
 recommended inputs to path validation.  For example, a policy
 constraints extension could be included in the self-signed
 certificate to indicate that paths beginning with this trust anchor
 should be trusted only for the specified policies.  Similarly, a name
 constraints extension could be included to indicate that paths
 beginning with this trust anchor should be trusted only for the
 specified name spaces.  The path validation algorithm presented in
 Section 6.1 does not assume that trust anchor information is provided
 in self-signed certificates and does not specify processing rules for
 additional information included in such certificates.
 Implementations that use self-signed certificates to specify trust
 anchor information are free to process or ignore such information.

6.3. CRL Validation

 This section describes the steps necessary to determine if a
 certificate is revoked 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 when processing CRLs that are issued in conformance with
 this profile.  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.

Cooper, et al. Standards Track [Page 90] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 cRLDistributionPoints and freshestCRL extensions to
         determine revocation status.
    (b)  use-deltas:  This boolean input determines whether delta CRLs
         are applied to CRLs.

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 minus 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.

Cooper, et al. Standards Track [Page 91] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 that 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's 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 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 and either the
                certificate or the CRL contains the freshest CRL
                extension, 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, use-deltas is set, and either the certificate or
            the CRL contains the freshest CRL extension, then obtain
            the current delta CRL that can be used to update the
            locally cached complete CRL as specified in Section 5.2.4.

Cooper, et al. Standards Track [Page 92] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 indirectCRL 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 the 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.

Cooper, et al. Standards Track [Page 93] RFC 5280 PKIX Certificate and CRL Profile May 2008

       (3)  Verify that the delta CRL authority key identifier
            extension matches the 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 the 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 the 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 are not included in the reasons_mask.
    (f)  Obtain and validate the certification path for the issuer of
         the complete CRL.  The trust anchor for the certification
         path MUST be the same as the trust anchor used to validate
         the target certificate.  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 5.3.3, then
         set the cert_status variable to the indicated reason as
         follows:

Cooper, et al. Standards Track [Page 94] RFC 5280 PKIX Certificate and CRL Profile May 2008

       (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 5.3.3, 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.
    (l)  Set the reasons_mask state variable to the union of its
         previous value and the value of the interim_reasons_mask
         state variable.
 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.  After processing such CRLs, if the revocation status has
 still not been determined, then return the cert_status UNDETERMINED.

7. Processing Rules for Internationalized Names

 Internationalized names may be encountered in numerous certificate
 and CRL fields and extensions, including distinguished names,
 internationalized domain names, electronic mail addresses, and
 Internationalized Resource Identifiers (IRIs).  Storage, comparison,
 and presentation of such names require special care.  Some characters
 may be encoded in multiple ways.  The same names could be represented
 in multiple encodings (e.g., ASCII or UTF8).  This section
 establishes conformance requirements for storage or comparison of
 each of these name forms.  Informative guidance on presentation is
 provided for some of these name forms.

Cooper, et al. Standards Track [Page 95] RFC 5280 PKIX Certificate and CRL Profile May 2008

7.1. Internationalized Names in Distinguished Names

 Representation of internationalized names in distinguished names is
 covered in Sections 4.1.2.4, Issuer Name, and 4.1.2.6, Subject Name.
 Standard naming attributes, such as common name, employ the
 DirectoryString type, which supports internationalized names through
 a variety of language encodings.  Conforming implementations MUST
 support UTF8String and PrintableString.  RFC 3280 required only
 binary comparison of attribute values encoded in UTF8String, however,
 this specification requires a more comprehensive handling of
 comparison.  Implementations may encounter certificates and CRLs with
 names encoded using TeletexString, BMPString, or UniversalString, but
 support for these is OPTIONAL.
 Conforming implementations MUST use the LDAP StringPrep profile
 (including insignificant space handling), as specified in [RFC4518],
 as the basis for comparison of distinguished name attributes encoded
 in either PrintableString or UTF8String.  Conforming implementations
 MUST support name comparisons using caseIgnoreMatch.  Support for
 attribute types that use other equality matching rules is optional.
 Before comparing names using the caseIgnoreMatch matching rule,
 conforming implementations MUST perform the six-step string
 preparation algorithm described in [RFC4518] for each attribute of
 type DirectoryString, with the following clarifications:
  • In step 2, Map, the mapping shall include case folding as

specified in Appendix B.2 of [RFC3454].

  • In step 6, Insignificant Character Removal, perform white space

compression as specified in Section 2.6.1, Insignificant Space

       Handling, of [RFC4518].
 When performing the string preparation algorithm, attributes MUST be
 treated as stored values.
 Comparisons of domainComponent attributes MUST be performed as
 specified in Section 7.3.
 Two naming attributes match if the attribute types are the same and
 the values of the attributes are an exact match after processing with
 the string preparation algorithm.  Two relative distinguished names
 RDN1 and RDN2 match if they have the same number of naming attributes
 and for each naming attribute in RDN1 there is a matching naming
 attribute in RDN2.  Two distinguished names DN1 and DN2 match if they
 have the same number of RDNs, for each RDN in DN1 there is a matching
 RDN in DN2, and the matching RDNs appear in the same order in both
 DNs.  A distinguished name DN1 is within the subtree defined by the

Cooper, et al. Standards Track [Page 96] RFC 5280 PKIX Certificate and CRL Profile May 2008

 distinguished name DN2 if DN1 contains at least as many RDNs as DN2,
 and DN1 and DN2 are a match when trailing RDNs in DN1 are ignored.

7.2. Internationalized Domain Names in GeneralName

 Internationalized Domain Names (IDNs) may be included in certificates
 and CRLs in the subjectAltName and issuerAltName extensions, name
 constraints extension, authority information access extension,
 subject information access extension, CRL distribution points
 extension, and issuing distribution point extension.  Each of these
 extensions uses the GeneralName type; one choice in GeneralName is
 the dNSName field, which is defined as type IA5String.
 IA5String is limited to the set of ASCII characters.  To accommodate
 internationalized domain names in the current structure, conforming
 implementations MUST convert internationalized domain names to the
 ASCII Compatible Encoding (ACE) format as specified in Section 4 of
 RFC 3490 before storage in the dNSName field.  Specifically,
 conforming implementations MUST perform the conversion operation
 specified in Section 4 of RFC 3490, with the following
 clarifications:
  • in step 1, the domain name SHALL be considered a "stored

string". That is, the AllowUnassigned flag SHALL NOT be set;

  • in step 3, set the flag called "UseSTD3ASCIIRules";
  • in step 4, process each label with the "ToASCII" operation; and
  • in step 5, change all label separators to U+002E (full stop).
 When comparing DNS names for equality, conforming implementations
 MUST perform a case-insensitive exact match on the entire DNS name.
 When evaluating name constraints, conforming implementations MUST
 perform a case-insensitive exact match on a label-by-label basis.  As
 noted in Section 4.2.1.10, any DNS name that may be constructed by
 adding labels to the left-hand side of the domain name given as the
 constraint is considered to fall within the indicated subtree.
 Implementations should convert IDNs to Unicode before display.
 Specifically, conforming implementations should perform the
 conversion operation specified in Section 4 of RFC 3490, with the
 following clarifications:
  • in step 1, the domain name SHALL be considered a "stored

string". That is, the AllowUnassigned flag SHALL NOT be set;

  • in step 3, set the flag called "UseSTD3ASCIIRules";

Cooper, et al. Standards Track [Page 97] RFC 5280 PKIX Certificate and CRL Profile May 2008

  • in step 4, process each label with the "ToUnicode" operation;

and

  • skip step 5.
 Note:  Implementations MUST allow for increased space requirements
 for IDNs.  An IDN ACE label will begin with the four additional
 characters "xn--" and may require as many as five ASCII characters to
 specify a single international character.

7.3. Internationalized Domain Names in Distinguished Names

 Domain Names may also be represented as distinguished names using
 domain components in the subject field, the issuer field, the
 subjectAltName extension, or the issuerAltName extension.  As with
 the dNSName in the GeneralName type, the value of this attribute is
 defined as an IA5String.  Each domainComponent attribute represents a
 single label.  To represent a label from an IDN in the distinguished
 name, the implementation MUST perform the "ToASCII" label conversion
 specified in Section 4.1 of RFC 3490.  The label SHALL be considered
 a "stored string".  That is, the AllowUnassigned flag SHALL NOT be
 set.
 Conforming implementations shall perform a case-insensitive exact
 match when comparing domainComponent attributes in distinguished
 names, as described in Section 7.2.
 Implementations should convert ACE labels to Unicode before display.
 Specifically, conforming implementations should perform the
 "ToUnicode" conversion operation specified, as described in Section
 7.2, on each ACE label before displaying the name.

7.4. Internationalized Resource Identifiers

 Internationalized Resource Identifiers (IRIs) are the
 internationalized complement to the Uniform Resource Identifier
 (URI).  IRIs are sequences of characters from Unicode, while URIs are
 sequences of characters from the ASCII character set.  [RFC3987]
 defines a mapping from IRIs to URIs.  While IRIs are not encoded
 directly in any certificate fields or extensions, their mapped URIs
 may be included in certificates and CRLs.  URIs may appear in the
 subjectAltName and issuerAltName extensions, name constraints
 extension, authority information access extension, subject
 information access extension, issuing distribution point extension,
 and CRL distribution points extension.  Each of these extensions uses
 the GeneralName type; URIs are encoded in the
 uniformResourceIdentifier field in GeneralName, which is defined as
 type IA5String.

Cooper, et al. Standards Track [Page 98] RFC 5280 PKIX Certificate and CRL Profile May 2008

 To accommodate IRIs in the current structure, conforming
 implementations MUST map IRIs to URIs as specified in Section 3.1 of
 [RFC3987], with the following clarifications:
  • in step 1, generate a UCS character sequence from the original

IRI format normalizing according to the NFC as specified in

       Variant b (normalization according to NFC);
  • perform step 2 using the output from step 1.
 Implementations MUST NOT convert the ireg-name component before
 performing step 2.
 Before URIs may be compared, conforming implementations MUST perform
 a combination of the syntax-based and scheme-based normalization
 techniques described in [RFC3987].  Specifically, conforming
 implementations MUST prepare URIs for comparison as follows:
  • Step 1: Where IRIs allow the usage of IDNs, those names MUST be

converted to ASCII Compatible Encoding as specified in Section

       7.2 above.
  • Step 2: The scheme and host are normalized to lowercase, as

described in Section 5.3.2.1 of [RFC3987].

  • Step 3: Perform percent-encoding normalization, as specified in

Section 5.3.2.3 of [RFC3987].

  • Step 4: Perform path segment normalization, as specified in

Section 5.3.2.4 of [RFC3987].

  • Step 5: If recognized, the implementation MUST perform scheme-

based normalization as specified in Section 5.3.3 of [RFC3987].

 Conforming implementations MUST recognize and perform scheme-based
 normalization for the following schemes: ldap, http, https, and ftp.
 If the scheme is not recognized, step 5 is omitted.
 When comparing URIs for equivalence, conforming implementations shall
 perform a case-sensitive exact match.
 Implementations should convert URIs to Unicode before display.
 Specifically, conforming implementations should perform the
 conversion operation specified in Section 3.2 of [RFC3987].

Cooper, et al. Standards Track [Page 99] RFC 5280 PKIX Certificate and CRL Profile May 2008

7.5. Internationalized Electronic Mail Addresses

 Electronic Mail addresses may be included in certificates and CRLs in
 the subjectAltName and issuerAltName extensions, name constraints
 extension, authority information access extension, subject
 information access extension, issuing distribution point extension,
 or CRL distribution points extension.  Each of these extensions uses
 the GeneralName construct; GeneralName includes the rfc822Name
 choice, which is defined as type IA5String.  To accommodate email
 addresses with internationalized domain names using the current
 structure, conforming implementations MUST convert the addresses into
 an ASCII representation.
 Where the host-part (the Domain of the Mailbox) contains an
 internationalized name, the domain name MUST be converted from an IDN
 to the ASCII Compatible Encoding (ACE) format as specified in Section
 7.2.
 Two email addresses are considered to match if:
    1)  the local-part of each name is an exact match, AND
    2)  the host-part of each name matches using a case-insensitive
        ASCII comparison.
 Implementations should convert the host-part of internationalized
 email addresses specified in these extensions to Unicode before
 display.  Specifically, conforming implementations should perform the
 conversion of the host-part of the Mailbox as described in Section
 7.2.

8. 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

Cooper, et al. Standards Track [Page 100] RFC 5280 PKIX Certificate and CRL Profile May 2008

 parties might wish to review the CA's certification 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., Secure Sockets Layer
 (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 that 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

Cooper, et al. Standards Track [Page 101] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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

Cooper, et al. Standards Track [Page 102] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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.
 In general, using the nameConstraints extension to constrain one name
 form (e.g., DNS names) offers no protection against use of other name
 forms (e.g., electronic mail addresses).
 While X.509 mandates that names be unambiguous, there is a risk that
 two unrelated authorities will issue certificates and/or CRLs under
 the same issuer name.  As a means of reducing problems and security
 issues related to issuer name collisions, CA and CRL issuer names
 SHOULD be formed in a way that reduces the likelihood of name
 collisions.  Implementers should take into account the possible
 existence of multiple unrelated CAs and CRL issuers with the same
 name.  At a minimum, implementations validating CRLs MUST ensure that
 the certification path of a certificate and the CRL issuer
 certification path used to validate the certificate terminate at the
 same trust anchor.
 While the local-part of an electronic mail address is case sensitive
 [RFC2821], emailAddress attribute values are not case sensitive
 [RFC2985].  As a result, there is a risk that two different email
 addresses will be treated as the same address when the matching rule
 for the emailAddress attribute is used, if the email server exploits
 the case sensitivity of mailbox local-parts.  Implementers should not
 include an email address in the emailAddress attribute if the email
 server that hosts the email address treats the local-part of email
 addresses as case sensitive.
 Implementers should be aware of risks involved if the CRL
 distribution points or authority information access extensions of

Cooper, et al. Standards Track [Page 103] RFC 5280 PKIX Certificate and CRL Profile May 2008

 corrupted certificates or CRLs contain links to malicious code.
 Implementers should always take the steps of validating the retrieved
 data to ensure that the data is properly formed.
 When certificates include a cRLDistributionPoints extension with an
 https URI or similar scheme, circular dependencies can be introduced.
 The relying party is forced to perform an additional path validation
 in order to obtain the CRL required to complete the initial path
 validation!  Circular conditions can also be created with an https
 URI (or similar scheme) in the authorityInfoAccess or
 subjectInfoAccess extensions.  At worst, this situation can create
 unresolvable dependencies.
 CAs SHOULD NOT include URIs that specify https, ldaps, or similar
 schemes in extensions.  CAs that include an https URI in one of these
 extensions MUST ensure that the server's certificate can be validated
 without using the information that is pointed to by the URI.  Relying
 parties that choose to validate the server's certificate when
 obtaining information pointed to by an https URI in the
 cRLDistributionPoints, authorityInfoAccess, or subjectInfoAccess
 extensions MUST be prepared for the possibility that this will result
 in unbounded recursion.
 Self-issued certificates provide CAs with one automated mechanism to
 indicate changes in the CA's operations.  In particular, self-issued
 certificates may be used to implement a graceful change-over from one
 non-compromised CA key pair to the next.  Detailed procedures for "CA
 key update" are specified in [RFC4210], where the CA protects its new
 public key using its previous private key and vice versa using two
 self-issued certificates.  Conforming client implementations will
 process the self-issued certificate and determine whether
 certificates issued under the new key may be trusted.  Self-issued
 certificates MAY be used to support other changes in CA operations,
 such as additions to the CA's policy set, using similar procedures.
 Some legacy implementations support names encoded in the ISO 8859-1
 character set (Latin1String) [ISO8859] but tag them as TeletexString.
 TeletexString encodes a larger character set than ISO 8859-1, but it
 encodes some characters differently.  The name comparison rules
 specified in Section 7.1 assume that TeletexStrings are encoded as
 described in the ASN.1 standard.  When comparing names encoded using
 the Latin1String character set, false positives and negatives are
 possible.
 When strings are mapped from internal representations to visual
 representations, sometimes two different strings will have the same
 or similar visual representations.  This can happen for many
 different reasons, including use of similar glyphs and use of

Cooper, et al. Standards Track [Page 104] RFC 5280 PKIX Certificate and CRL Profile May 2008

 composed characters (such as e + ' equaling U+00E9, the Korean
 composed characters, and vowels above consonant clusters in certain
 languages).  As a result of this situation, people doing visual
 comparisons between two different names may think they are the same
 when in fact they are not.  Also, people may mistake one string for
 another.  Issuers of certificates and relying parties both need to be
 aware of this situation.

9. IANA Considerations

 Extensions in certificates and CRLs are identified using object
 identifiers.  The objects are defined in an arc delegated by IANA to
 the PKIX Working Group.  No further action by IANA is necessary for
 this document or any anticipated updates.

10. Acknowledgments

 Warwick Ford participated with the authors in some of the design team
 meetings that directed development of this document.  The design
 team's efforts were guided by contributions from Matt Crawford, Tom
 Gindin, Steve Hanna, Stephen Henson, Paul Hoffman, Takashi Ito, Denis
 Pinkas, and Wen-Cheng Wang.

11. References

11.1. Normative References

 [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791, September
            1981.
 [RFC1034]  Mockapetris, P., "Domain Names - Concepts and Facilities",
            STD 13, RFC 1034, November 1987.
 [RFC1123]  Braden, R., Ed., "Requirements for Internet Hosts --
            Application and Support", STD 3, RFC 1123, October 1989.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998.
 [RFC2585]  Housley, R. and P. Hoffman, "Internet X.509 Public Key
            Infrastructure: Operational Protocols: FTP and HTTP", RFC
            2585, May 1999.

Cooper, et al. Standards Track [Page 105] RFC 5280 PKIX Certificate and CRL Profile May 2008

 [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
            Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
            Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
 [RFC2797]  Myers, M., Liu, X., Schaad, J., and J. Weinstein,
            "Certificate Management Messages over CMS", RFC 2797,
            April 2000.
 [RFC2821]  Klensin, J., Ed., "Simple Mail Transfer Protocol", RFC
            2821, April 2001.
 [RFC3454]  Hoffman, P. and M. Blanchet, "Preparation of
            Internationalized Strings ("stringprep")", RFC 3454,
            December 2002.
 [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
            "Internationalizing Domain Names in Applications (IDNA)",
            RFC 3490, March 2003.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, November 2003.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66, RFC
            3986, January 2005.
 [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
            Identifiers (IRIs)", RFC 3987, January 2005.
 [RFC4516]  Smith, M., Ed., and T. Howes, "Lightweight Directory
            Access Protocol (LDAP): Uniform Resource Locator", RFC
            4516, June 2006.
 [RFC4518]  Zeilenga, K., "Lightweight Directory Access Protocol
            (LDAP): Internationalized String Preparation", RFC 4518,
            June 2006.
 [RFC4523]  Zeilenga, K., "Lightweight Directory Access Protocol
            (LDAP) Schema Definitions for X.509 Certificates", RFC
            4523, June 2006.
 [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
            (CIDR): The Internet Address Assignment and Aggregation
            Plan", BCP 122, RFC 4632, August 2006.
 [X.680]    ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002,
            Information technology - Abstract Syntax Notation One
            (ASN.1):  Specification of basic notation.

Cooper, et al. Standards Track [Page 106] RFC 5280 PKIX Certificate and CRL Profile May 2008

 [X.690]    ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
            Information technology - ASN.1 encoding rules:
            Specification of Basic Encoding Rules (BER), Canonical
            Encoding Rules (CER) and Distinguished Encoding Rules
            (DER).

11.2. Informative References

 [ISO8859]  ISO/IEC 8859-1:1998.  Information technology -- 8-bit
            single-byte coded graphic character sets -- Part 1: Latin
            alphabet No. 1.
 [ISO10646] ISO/IEC 10646:2003.  Information technology -- Universal
            Multiple-Octet Coded Character Set (UCS).
 [NFC]      Davis, M. and M. Duerst, "Unicode Standard Annex #15:
            Unicode Normalization Forms", October 2006,
            <http://www.unicode.org/reports/tr15/>.
 [RFC1422]  Kent, S., "Privacy Enhancement for Internet Electronic
            Mail: Part II: Certificate-Based Key Management", RFC
            1422, February 1993.
 [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
            Languages", BCP 18, RFC 2277, January 1998.
 [RFC2459]  Housley, R., Ford, W., Polk, W., and D. Solo, "Internet
            X.509 Public Key Infrastructure Certificate and CRL
            Profile", RFC 2459, January 1999.
 [RFC2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
            Adams, "X.509 Internet Public Key Infrastructure Online
            Certificate Status Protocol - OCSP", RFC 2560, June 1999.
 [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
            Classes and Attribute Types Version 2.0", RFC 2985,
            November 2000.
 [RFC3161]  Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
            "Internet X.509 Public Key Infrastructure Time-Stamp
            Protocol (TSP)", RFC 3161, August 2001.
 [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
            Identifiers for the Internet X.509 Public Key
            Infrastructure Certificate and Certificate Revocation List
            (CRL) Profile", RFC 3279, April 2002.

Cooper, et al. Standards Track [Page 107] RFC 5280 PKIX Certificate and CRL Profile May 2008

 [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
            X.509 Public Key Infrastructure Certificate and
            Certificate Revocation List (CRL) Profile", RFC 3280,
            April 2002.
 [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
            Algorithms and Identifiers for RSA Cryptography for use in
            the Internet X.509 Public Key Infrastructure Certificate
            and Certificate Revocation List (CRL) Profile", RFC 4055,
            June 2005.
 [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
            Kerberos Network Authentication Service (V5)", RFC 4120,
            July 2005.
 [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
            "Internet X.509 Public Key Infrastructure Certificate
            Management Protocol (CMP)", RFC 4210, September 2005.
 [RFC4325]  Santesson, S. and R. Housley, "Internet X.509 Public Key
            Infrastructure Authority Information Access Certificate
            Revocation List (CRL) Extension", RFC 4325, December 2005.
 [RFC4491]  Leontiev, S., Ed., and D. Shefanovski, Ed., "Using the
            GOST R 34.10-94, GOST R 34.10-2001, and GOST R 34.11-94
            Algorithms with the Internet X.509 Public Key
            Infrastructure Certificate and CRL Profile", RFC 4491, May
            2006.
 [RFC4510]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
            (LDAP): Technical Specification Road Map", RFC 4510, June
            2006.
 [RFC4512]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
            (LDAP): Directory Information Models", RFC 4512, June
            2006.
 [RFC4514]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
            (LDAP): String Representation of Distinguished Names", RFC
            4514, June 2006.
 [RFC4519]  Sciberras, A., Ed., "Lightweight Directory Access Protocol
            (LDAP): Schema for User Applications", RFC 4519, June
            2006.

Cooper, et al. Standards Track [Page 108] RFC 5280 PKIX Certificate and CRL Profile May 2008

 [RFC4630]  Housley, R. and S. Santesson, "Update to DirectoryString
            Processing in the Internet X.509 Public Key Infrastructure
            Certificate and Certificate Revocation List (CRL)
            Profile", RFC 4630, August 2006.
 [X.500]    ITU-T Recommendation X.500 (2005) | ISO/IEC 9594-1:2005,
            Information technology - Open Systems Interconnection -
            The Directory: Overview of concepts, models and services.
 [X.501]    ITU-T Recommendation X.501 (2005) | ISO/IEC 9594-2:2005,
            Information technology - Open Systems Interconnection -
            The Directory: Models.
 [X.509]    ITU-T Recommendation X.509 (2005) | ISO/IEC 9594-8:2005,
            Information technology - Open Systems Interconnection -
            The Directory: Public-key and attribute certificate
            frameworks.
 [X.520]    ITU-T Recommendation X.520 (2005) | ISO/IEC 9594-6:2005,
            Information technology - Open Systems Interconnection -
            The Directory: Selected attribute types.
 [X.660]    ITU-T Recommendation X.660 (2004) | ISO/IEC 9834-1:2005,
            Information technology - Open Systems Interconnection -
            Procedures for the operation of OSI Registration
            Authorities: General procedures, and top arcs of the ASN.1
            Object Identifier tree.
 [X.683]    ITU-T Recommendation X.683 (2002) | ISO/IEC 8824-4:2002,
            Information technology - Abstract Syntax Notation One
            (ASN.1): Parameterization of ASN.1 specifications.
 [X9.55]    ANSI X9.55-1997, Public Key Cryptography for the Financial
            Services Industry: Extensions to Public Key Certificates
            and Certificate Revocation Lists, January 1997.

Cooper, et al. Standards Track [Page 109] RFC 5280 PKIX Certificate and CRL Profile May 2008

Appendix A. Pseudo-ASN.1 Structures and OIDs

 This appendix 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

  1. - UniversalString is defined in ASN.1:1993

BMPString ::= [UNIVERSAL 30] IMPLICIT OCTET STRING

  1. - BMPString is the subtype of UniversalString and models
  2. - the Basic Multilingual Plane of ISO/IEC 10646

UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING

  1. - The content of this type conforms to RFC 3629.

– PKIX specific OIDs

id-pkix OBJECT IDENTIFIER ::=

       { iso(1) identified-organization(3) dod(6) internet(1)
                  security(5) mechanisms(5) pkix(7) }

Cooper, et al. Standards Track [Page 110] RFC 5280 PKIX Certificate and CRL Profile May 2008

– PKIX arcs

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

  1. - arc for private certificate extensions

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

  1. - arc for policy qualifier types

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

  1. - arc for extended key purpose OIDS

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

  1. - arc for access descriptors

– policyQualifierIds for Internet policy qualifiers

id-qt-cps OBJECT IDENTIFIER ::= { id-qt 1 }

  1. - OID for CPS qualifier

id-qt-unotice OBJECT IDENTIFIER ::= { id-qt 2 }

  1. - 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 – DEFINED BY AttributeType

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

Cooper, et al. Standards Track [Page 111] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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 }

– Naming attributes of type X520Name: – X520name ::= DirectoryString (SIZE (1..ub-name)) – – Expanded to avoid parameterized type: 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 }

– Naming attributes of type X520CommonName: – X520CommonName ::= DirectoryName (SIZE (1..ub-common-name)) – – Expanded to avoid parameterized type: 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)) }

Cooper, et al. Standards Track [Page 112] RFC 5280 PKIX Certificate and CRL Profile May 2008

– Naming attributes of type X520LocalityName

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

– Naming attributes of type X520LocalityName: – X520LocalityName ::= DirectoryName (SIZE (1..ub-locality-name)) – – Expanded to avoid parameterized type: 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 }

– Naming attributes of type X520StateOrProvinceName: – X520StateOrProvinceName ::= DirectoryName (SIZE (1..ub-state-name)) – – Expanded to avoid parameterized type: 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)) }

Cooper, et al. Standards Track [Page 113] RFC 5280 PKIX Certificate and CRL Profile May 2008

– Naming attributes of type X520OrganizationName

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

– Naming attributes of type X520OrganizationName: – X520OrganizationName ::= – DirectoryName (SIZE (1..ub-organization-name)) – – Expanded to avoid parameterized type: 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 }

– Naming attributes of type X520OrganizationalUnitName: – X520OrganizationalUnitName ::= – DirectoryName (SIZE (1..ub-organizational-unit-name)) – – Expanded to avoid parameterized type: 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)) }

Cooper, et al. Standards Track [Page 114] RFC 5280 PKIX Certificate and CRL Profile May 2008

– Naming attributes of type X520Title

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

– Naming attributes of type X520Title: – X520Title ::= DirectoryName (SIZE (1..ub-title)) – – Expanded to avoid parameterized type: 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 }

– Naming attributes of type X520Pseudonym: – X520Pseudonym ::= DirectoryName (SIZE (1..ub-pseudonym)) – – Expanded to avoid parameterized type: 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)) }

Cooper, et al. Standards Track [Page 115] RFC 5280 PKIX Certificate and CRL Profile May 2008

– Naming attributes of type DomainComponent (from RFC 4519)

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  }

Cooper, et al. Standards Track [Page 116] RFC 5280 PKIX Certificate and CRL Profile May 2008

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
               -- contains the DER encoding of an ASN.1 value
               -- corresponding to the extension type identified
               -- by extnID
   }

Cooper, et al. Standards Track [Page 117] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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, version MUST be v2
                             }  OPTIONAL,
   crlExtensions           [0] Extensions OPTIONAL }
                                 -- if present, version 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 }

Cooper, et al. Standards Track [Page 118] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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))

Cooper, et al. Standards Track [Page 119] RFC 5280 PKIX Certificate and CRL Profile May 2008

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))

Cooper, et al. Standards Track [Page 120] RFC 5280 PKIX Certificate and CRL Profile May 2008

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

Cooper, et al. Standards Track [Page 121] RFC 5280 PKIX Certificate and CRL Profile May 2008

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

Cooper, et al. Standards Track [Page 122] RFC 5280 PKIX Certificate and CRL Profile May 2008

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)) }

Cooper, et al. Standards Track [Page 123] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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 ::= 255 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

Cooper, et al. Standards Track [Page 124] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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

Cooper, et al. Standards Track [Page 125] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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),  -- recent editions of X.509 have
                              -- renamed this bit to contentCommitment
   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

Cooper, et al. Standards Track [Page 126] RFC 5280 PKIX Certificate and CRL Profile May 2008

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

Cooper, et al. Standards Track [Page 127] RFC 5280 PKIX Certificate and CRL Profile May 2008

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 }

Cooper, et al. Standards Track [Page 128] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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 }

Cooper, et al. Standards Track [Page 129] RFC 5280 PKIX Certificate and CRL Profile May 2008

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

Cooper, et al. Standards Track [Page 130] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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 }
   -- at most one of onlyContainsUserCerts, onlyContainsCACerts,
   -- and onlyContainsAttributeCerts may be set to TRUE.

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

BaseCRLNumber ::= CRLNumber

Cooper, et al. Standards Track [Page 131] RFC 5280 PKIX Certificate and CRL Profile May 2008

– reason code 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 arc holdinstruction arc

holdInstruction OBJECT IDENTIFIER ::=

        {joint-iso-itu-t(2) member-body(2) us(840) x9cm(10040) 2}

– ANSI X9 holdinstructions

id-holdinstruction-none OBJECT IDENTIFIER ::=

                                    {holdInstruction 1} -- deprecated

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

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

Cooper, et al. Standards Track [Page 132] RFC 5280 PKIX Certificate and CRL Profile May 2008

– 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.  Conforming 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.  Conforming 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 that the upper bound is unspecified.
 Implementations are free to choose an upper bound that suits their
 environment.
 The character string type PrintableString supports a very basic Latin
 character set: the lowercase letters 'a' through 'z', uppercase
 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 that include
 either the at sign or underscore character as PrintableString.

Cooper, et al. Standards Track [Page 133] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 zeros 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 [ISO10646].  ISO 10646 is the Universal
 multiple-octet coded Character Set (UCS).
 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].  UTF8String is a
 universal type and has been assigned tag number 12.  The content of
 UTF8String was defined by RFC 2044 and updated in RFC 2279, which was
 updated in [RFC3629].
 In anticipation of these changes, and in conformance with IETF Best
 Practices codified in [RFC2277], IETF Policy on Character Sets and
 Languages, this document includes UTF8String as a choice in
 DirectoryString and in the userNotice certificate policy qualifier.
 For many of the attribute types defined in [X.520], the
 AttributeValue uses the DirectoryString type.  Of the attributes
 specified in Appendix A, the name, surname, givenName, initials,
 generationQualifier, commonName, localityName, stateOrProvinceName,
 organizationName, organizationalUnitName, title, and pseudonym
 attributes all use the DirectoryString type.  X.520 uses a
 parameterized type definition [X.683] of DirectoryString to specify
 the syntax for each of these attributes.  The parameter is used to
 indicate the maximum string length allowed for the attribute.  In
 Appendix A, in order to avoid the use of parameterized type
 definitions, the DirectoryString type is written in its expanded form
 for the definition of each of these attribute types.  So, the ASN.1
 in Appendix A describes the syntax for each of these attributes as
 being a CHOICE of TeletexString, PrintableString, UniversalString,
 UTF8String, and BMPString, with the appropriate constraints on the
 string length applied to each of the types in the CHOICE, rather than
 using the ASN.1 type DirectoryString to describe the syntax.

Cooper, et al. Standards Track [Page 134] RFC 5280 PKIX Certificate and CRL Profile May 2008

 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 that 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 Section 1.4
 of [RFC4512]) 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 that
 contain OIDs that exceed these requirements.  Likewise, CRL issuers
 SHOULD NOT issue CRLs that contain OIDs that exceed these
 requirements.
 The content-specific rules for encoding GeneralName field values in
 the nameConstraints extension differ from rules that apply in other
 extensions.  In all other certificate, CRL, and CRL entry extensions
 specified in this document the encoding rules conform to the rules
 for the underlying type.  For example, values in the
 uniformResourceIdentifier field must contain a valid URI as specified
 in [RFC3986].  The content-specific rules for encoding values in the
 nameConstraints extension are specified in Section 4.2.1.10, and
 these rules may not conform to the rules for the underlying type.
 For example, when the uniformResourceIdentifier field appears in a
 nameConstraints extension, it must hold a DNS name (e.g.,
 "host.example.com" or ".example.com") rather than a URI.
 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 [RFC2459], 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 as critical, those unknown
 elements ought to be ignored, as follows:

Cooper, et al. Standards Track [Page 135] RFC 5280 PKIX Certificate and CRL Profile May 2008

    (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 as critical,
 the implementation MUST reject the certificate or CRL containing the
 unrecognized extension.

Appendix C. Examples

 This appendix contains four examples: three certificates and a CRL.
 The first two certificates and the CRL comprise a minimal
 certification path.
 Appendix C.1 contains an annotated hex dump of a "self-signed"
 certificate issued by a CA whose distinguished name is
 cn=Example CA,dc=example,dc=com.  The certificate contains an RSA
 public key, and is signed by the corresponding RSA private key.
 Appendix C.2 contains an annotated hex dump of an end entity
 certificate.  The end entity certificate contains an RSA public key,
 and is signed by the private key corresponding to the "self-signed"
 certificate in Appendix C.1.
 Appendix C.3 contains an annotated hex dump of an end entity
 certificate that contains a DSA public key with parameters, and is
 signed with DSA and SHA-1.  This certificate is not part of the
 minimal certification path.
 Appendix C.4 contains an annotated hex dump of a CRL.  The CRL is
 issued by the CA whose distinguished name is
 cn=Example CA,dc=example,dc=com and the list of revoked certificates
 includes the end entity certificate presented in Appendix C.2.
 The certificates were processed using Peter Gutmann'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/groups/ST/crypto_apps_infra/documents/pkixtools.

Cooper, et al. Standards Track [Page 136] RFC 5280 PKIX Certificate and CRL Profile May 2008

 In places in this appendix where a distinguished name is specified
 using a string representation, the strings are formatted using the
 rules specified in [RFC4514].

C.1. RSA Self-Signed Certificate

 This appendix contains an annotated hex dump of a 578 byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 17;
 (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is
      cn=Example CA,dc=example,dc=com;
 (d)  the subject's distinguished name is
      cn=Example CA,dc=example,dc=com;
 (e)  the certificate was issued on April 30, 2004 and expired on
      April 30, 2005;
 (f)  the certificate contains a 1024-bit RSA public key;
 (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  574: SEQUENCE {
 4  423:   SEQUENCE {
 8    3:     [0] {
10    1:       INTEGER 2
       :       }
13    1:     INTEGER 17
16   13:     SEQUENCE {
18    9:       OBJECT IDENTIFIER
       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
29    0:       NULL
       :       }
31   67:     SEQUENCE {
33   19:       SET {
35   17:         SEQUENCE {
37   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
49    3:           IA5String 'com'
       :           }
       :         }
54   23:       SET {
56   21:         SEQUENCE {
58   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
70    7:           IA5String 'example'
       :           }

Cooper, et al. Standards Track [Page 137] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :         }
79   19:       SET {
81   17:         SEQUENCE {
83    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
88   10:           PrintableString 'Example CA'
       :           }
       :         }
       :       }

100 30: SEQUENCE { 102 13: UTCTime 30/04/2004 14:25:34 GMT 117 13: UTCTime 30/04/2005 14:25:34 GMT

       :       }

132 67: SEQUENCE { 134 19: SET { 136 17: SEQUENCE { 138 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

150 3: IA5String 'com'

       :           }
       :         }

155 23: SET { 157 21: SEQUENCE { 159 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

171 7: IA5String 'example'

       :           }
       :         }

180 19: SET { 182 17: SEQUENCE { 184 3: OBJECT IDENTIFIER commonName (2 5 4 3) 189 10: PrintableString 'Example CA'

       :           }
       :         }
       :       }

201 159: SEQUENCE { 204 13: SEQUENCE { 206 9: OBJECT IDENTIFIER

       :           rsaEncryption (1 2 840 113549 1 1 1)

217 0: NULL

       :         }

219 141: BIT STRING, encapsulates { 223 137: SEQUENCE { 226 129: INTEGER

       :             00 C2 D7 97 6D 28 70 AA 5B CF 23 2E 80 70 39 EE
       :             DB 6F D5 2D D5 6A 4F 7A 34 2D F9 22 72 47 70 1D
       :             EF 80 E9 CA 30 8C 00 C4 9A 6E 5B 45 B4 6E A5 E6
       :             6C 94 0D FA 91 E9 40 FC 25 9D C7 B7 68 19 56 8F
       :             11 70 6A D7 F1 C9 11 4F 3A 7E 3F 99 8D 6E 76 A5

Cooper, et al. Standards Track [Page 138] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :             74 5F 5E A4 55 53 E5 C7 68 36 53 C7 1D 3B 12 A6
       :             85 FE BD 6E A1 CA DF 35 50 AC 08 D7 B9 B4 7E 5C
       :             FE E2 A3 2C D1 23 84 AA 98 C0 9B 66 18 9A 68 47
       :             E9

358 3: INTEGER 65537

       :           }
       :         }
       :       }

363 66: [3] { 365 64: SEQUENCE { 367 29: SEQUENCE { 369 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14) 374 22: OCTET STRING, encapsulates { 376 20: OCTET STRING

       :               08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A 4A
       :               20 84 2C 32
       :             }
       :           }

398 14: SEQUENCE { 400 3: OBJECT IDENTIFIER keyUsage (2 5 29 15) 405 1: BOOLEAN TRUE 408 4: OCTET STRING, encapsulates { 410 2: BIT STRING 1 unused bits

       :               '0000011'B
       :             }
       :           }

414 15: SEQUENCE { 416 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19) 421 1: BOOLEAN TRUE 424 5: OCTET STRING, encapsulates { 426 3: SEQUENCE { 428 1: BOOLEAN TRUE

       :               }
       :             }
       :           }
       :         }
       :       }
       :     }

431 13: SEQUENCE { 433 9: OBJECT IDENTIFIER

       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)

444 0: NULL

       :     }

446 129: BIT STRING

       :     6C F8 02 74 A6 61 E2 64 04 A6 54 0C 6C 72 13 AD
       :     3C 47 FB F6 65 13 A9 85 90 33 EA 76 A3 26 D9 FC
       :     D1 0E 15 5F 28 B7 EF 93 BF 3C F3 E2 3E 7C B9 52
       :     FC 16 6E 29 AA E1 F4 7A 6F D5 7F EF B3 95 CA F3

Cooper, et al. Standards Track [Page 139] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :     66 88 83 4E A1 35 45 84 CB BC 9B B8 C8 AD C5 5E
       :     46 D9 0B 0E 8D 80 E1 33 2B DC BE 2B 92 7E 4A 43
       :     A9 6A EF 8A 63 61 B3 6E 47 38 BE E8 0D A3 67 5D
       :     F3 FA 91 81 3C 92 BB C5 5F 25 25 EB 7C E7 D8 A1
       :   }

C.2. End Entity Certificate Using RSA

 This appendix contains an annotated hex dump of a 629-byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 18;
 (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is
      cn=Example CA,dc=example,dc=com;
 (d)  the subject's distinguished name is
      cn=End Entity,dc=example,dc=com;
 (e)  the certificate was valid from September 15, 2004 through March
      15, 2005;
 (f)  the certificate contains a 1024-bit RSA 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 electronic
      mail address (rfc822Name) of "end.entity@example.com".
 0  625: SEQUENCE {
 4  474:   SEQUENCE {
 8    3:     [0] {
10    1:       INTEGER 2
       :       }
13    1:     INTEGER 18
16   13:     SEQUENCE {
18    9:       OBJECT IDENTIFIER
       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
29    0:       NULL
       :       }
31   67:     SEQUENCE {
33   19:       SET {
35   17:         SEQUENCE {
37   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
49    3:           IA5String 'com'
       :           }
       :         }
54   23:       SET {

Cooper, et al. Standards Track [Page 140] RFC 5280 PKIX Certificate and CRL Profile May 2008

56   21:         SEQUENCE {
58   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
70    7:           IA5String 'example'
       :           }
       :         }
79   19:       SET {
81   17:         SEQUENCE {
83    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
88   10:           PrintableString 'Example CA'
       :           }
       :         }
       :       }

100 30: SEQUENCE { 102 13: UTCTime 15/09/2004 11:48:21 GMT 117 13: UTCTime 15/03/2005 11:48:21 GMT

       :       }

132 67: SEQUENCE { 134 19: SET { 136 17: SEQUENCE { 138 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

150 3: IA5String 'com'

       :           }
       :         }

155 23: SET { 157 21: SEQUENCE { 159 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

171 7: IA5String 'example'

       :           }
       :         }

180 19: SET { 182 17: SEQUENCE { 184 3: OBJECT IDENTIFIER commonName (2 5 4 3) 189 10: PrintableString 'End Entity'

       :           }
       :         }
       :       }

201 159: SEQUENCE { 204 13: SEQUENCE { 206 9: OBJECT IDENTIFIER

       :           rsaEncryption (1 2 840 113549 1 1 1)

217 0: NULL

       :         }

219 141: BIT STRING, encapsulates { 223 137: SEQUENCE { 226 129: INTEGER

Cooper, et al. Standards Track [Page 141] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :             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

358 3: INTEGER 65537

       :           }
       :         }
       :       }

363 117: [3] { 365 115: SEQUENCE { 367 33: SEQUENCE { 369 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) 374 26: OCTET STRING, encapsulates { 376 24: SEQUENCE { 378 22: [1] 'end.entity@example.com'

       :               }
       :             }
       :           }

402 29: SEQUENCE { 404 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14) 409 22: OCTET STRING, encapsulates { 411 20: OCTET STRING

       :               17 7B 92 30 FF 44 D6 66 E1 90 10 22 6C 16 4F C0
       :               8E 41 DD 6D
       :             }
       :           }

433 31: SEQUENCE { 435 3: OBJECT IDENTIFIER

       :             authorityKeyIdentifier (2 5 29 35)

440 24: OCTET STRING, encapsulates { 442 22: SEQUENCE { 444 20: [0]

       :                 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
       :                 4A 20 84 2C 32
       :               }
       :             }
       :           }

466 14: SEQUENCE { 468 3: OBJECT IDENTIFIER keyUsage (2 5 29 15) 473 1: BOOLEAN TRUE 476 4: OCTET STRING, encapsulates { 478 2: BIT STRING 6 unused bits

       :               '11'B

Cooper, et al. Standards Track [Page 142] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :             }
       :           }
       :         }
       :       }
       :     }

482 13: SEQUENCE { 484 9: OBJECT IDENTIFIER

       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)

495 0: NULL

       :     }

497 129: BIT STRING

       :     00 20 28 34 5B 68 32 01 BB 0A 36 0E AD 71 C5 95
       :     1A E1 04 CF AE AD C7 62 14 A4 1B 36 31 C0 E2 0C
       :     3D D9 1E C0 00 DC 10 A0 BA 85 6F 41 CB 62 7A B7
       :     4C 63 81 26 5E D2 80 45 5E 33 E7 70 45 3B 39 3B
       :     26 4A 9C 3B F2 26 36 69 08 79 BB FB 96 43 77 4B
       :     61 8B A1 AB 91 64 E0 F3 37 61 3C 1A A3 A4 C9 8A
       :     B2 BF 73 D4 4D E4 58 E4 62 EA BC 20 74 92 86 0E
       :     CE 84 60 76 E9 73 BB C7 85 D3 91 45 EA 62 5D CD
       :   }

C.3. End Entity Certificate Using DSA

 This appendix contains an annotated hex dump of a 914-byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 256;
 (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is cn=Example DSA
      CA,dc=example,dc=com;
 (d)  the subject's distinguished name is cn=DSA End
      Entity,dc=example,dc=com;
 (e)  the certificate was issued on May 2, 2004 and expired on May 2,
      2005;
 (f)  the certificate contains a 1024-bit DSA public key with
      parameters;
 (g)  the certificate is an end entity certificate (not a CA
      certificate);
 (h)  the certificate includes a subject alternative name of
      "<http://www.example.com/users/DSAendentity.html>" and an issuer
      alternative name of "<http://www.example.com>" -- both are URLs;

Cooper, et al. Standards Track [Page 143] RFC 5280 PKIX Certificate and CRL Profile May 2008

 (i)  the certificate includes 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  910: SEQUENCE {
 4  846:   SEQUENCE {
 8    3:     [0] {
10    1:       INTEGER 2
       :       }
13    2:     INTEGER 256
17    9:     SEQUENCE {
19    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
       :       }
28   71:     SEQUENCE {
30   19:       SET {
32   17:         SEQUENCE {
34   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
46    3:           IA5String 'com'
       :           }
       :         }
51   23:       SET {
53   21:         SEQUENCE {
55   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
67    7:           IA5String 'example'
       :           }
       :         }
76   23:       SET {
78   21:         SEQUENCE {
80    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
85   14:           PrintableString 'Example DSA CA'
       :           }
       :         }
       :       }

101 30: SEQUENCE { 103 13: UTCTime 02/05/2004 16:47:38 GMT 118 13: UTCTime 02/05/2005 16:47:38 GMT

       :       }

133 71: SEQUENCE { 135 19: SET { 137 17: SEQUENCE { 139 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

Cooper, et al. Standards Track [Page 144] RFC 5280 PKIX Certificate and CRL Profile May 2008

151 3: IA5String 'com'

       :           }
       :         }

156 23: SET { 158 21: SEQUENCE { 160 10: OBJECT IDENTIFIER

       :             domainComponent (0 9 2342 19200300 100 1 25)

172 7: IA5String 'example'

       :           }
       :         }

181 23: SET { 183 21: SEQUENCE { 185 3: OBJECT IDENTIFIER commonName (2 5 4 3) 190 14: PrintableString 'DSA End Entity'

       :           }
       :         }
       :       }

206 439: SEQUENCE { 210 300: SEQUENCE { 214 7: OBJECT IDENTIFIER dsa (1 2 840 10040 4 1) 223 287: SEQUENCE { 227 129: 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

359 21: INTEGER

       :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA 55 F7
       :             7D 57 74 81 E5

382 129: 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
       :           }
       :         }

514 132: BIT STRING, encapsulates { 518 128: INTEGER

Cooper, et al. Standards Track [Page 145] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :           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
       :         }
       :       }

649 202: [3] { 652 199: SEQUENCE { 655 57: SEQUENCE { 657 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) 662 50: OCTET STRING, encapsulates { 664 48: SEQUENCE { 666 46: [6]

       :                 'http://www.example.com/users/DSAendentity.'
       :                 'html'
       :               }
       :             }
       :           }

714 33: SEQUENCE { 716 3: OBJECT IDENTIFIER issuerAltName (2 5 29 18) 721 26: OCTET STRING, encapsulates { 723 24: SEQUENCE { 725 22: [6] 'http://www.example.com'

       :               }
       :             }
       :           }

749 29: SEQUENCE { 751 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14) 756 22: OCTET STRING, encapsulates { 758 20: OCTET STRING

       :               DD 25 66 96 43 AB 78 11 43 44 FE 95 16 F9 D9 B6
       :               B7 02 66 8D
       :             }
       :           }

780 31: SEQUENCE { 782 3: OBJECT IDENTIFIER

       :             authorityKeyIdentifier (2 5 29 35)

787 24: OCTET STRING, encapsulates { 789 22: SEQUENCE { 791 20: [0]

       :                 86 CA A5 22 81 62 EF AD 0A 89 BC AD 72 41 2C
       :                 29 49 F4 86 56
       :               }
       :             }

Cooper, et al. Standards Track [Page 146] RFC 5280 PKIX Certificate and CRL Profile May 2008

       :           }

813 23: SEQUENCE { 815 3: OBJECT IDENTIFIER certificatePolicies (2 5 29 32) 820 16: OCTET STRING, encapsulates { 822 14: SEQUENCE { 824 12: SEQUENCE { 826 10: OBJECT IDENTIFIER '2 16 840 1 101 3 2 1 48 9'

       :                 }
       :               }
       :             }
       :           }

838 14: SEQUENCE { 840 3: OBJECT IDENTIFIER keyUsage (2 5 29 15) 845 1: BOOLEAN TRUE 848 4: OCTET STRING, encapsulates { 850 2: BIT STRING 7 unused bits

       :               '1'B (bit 0)
       :             }
       :           }
       :         }
       :       }
       :     }

854 9: SEQUENCE { 856 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)

       :     }

865 47: BIT STRING, encapsulates { 868 44: SEQUENCE { 870 20: INTEGER

       :         65 57 07 34 DD DC CA CC 5E F4 02 F4 56 42 2C 5E
       :         E1 B3 3B 80

892 20: INTEGER

       :         60 F4 31 17 CA F4 CF FF EE F4 08 A7 D9 B2 61 BE
       :         B1 C3 DA BF
       :       }
       :     }
       :   }

C.4. Certificate Revocation List

 This appendix contains an annotated hex dump of a version 2 CRL with
 two extensions (cRLNumber and authorityKeyIdentifier).  The CRL was
 issued by cn=Example CA,dc=example,dc=com on February 5, 2005; the
 next scheduled issuance was February 6, 2005.  The CRL includes one
 revoked certificate: serial number 18, which was revoked on November
 19, 2004 due to keyCompromise.  The CRL itself is number 12, and it
 was signed with RSA and SHA-1.

Cooper, et al. Standards Track [Page 147] RFC 5280 PKIX Certificate and CRL Profile May 2008

 0  352: SEQUENCE {
 4  202:   SEQUENCE {
 7    1:     INTEGER 1
10   13:     SEQUENCE {
12    9:       OBJECT IDENTIFIER
       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)
23    0:       NULL
       :       }
25   67:     SEQUENCE {
27   19:       SET {
29   17:         SEQUENCE {
31   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
43    3:           IA5String 'com'
       :           }
       :         }
48   23:       SET {
50   21:         SEQUENCE {
52   10:           OBJECT IDENTIFIER
       :             domainComponent (0 9 2342 19200300 100 1 25)
64    7:           IA5String 'example'
       :           }
       :         }
73   19:       SET {
75   17:         SEQUENCE {
77    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
82   10:           PrintableString 'Example CA'
       :           }
       :         }
       :       }
94   13:     UTCTime 05/02/2005 12:00:00 GMT

109 13: UTCTime 06/02/2005 12:00:00 GMT 124 34: SEQUENCE { 126 32: SEQUENCE { 128 1: INTEGER 18 131 13: UTCTime 19/11/2004 15:57:03 GMT 146 12: SEQUENCE { 148 10: SEQUENCE { 150 3: OBJECT IDENTIFIER cRLReason (2 5 29 21) 155 3: OCTET STRING, encapsulates { 157 1: ENUMERATED 1

       :               }
       :             }
       :           }
       :         }
       :       }

160 47: [0] { 162 45: SEQUENCE {

Cooper, et al. Standards Track [Page 148] RFC 5280 PKIX Certificate and CRL Profile May 2008

164 31: SEQUENCE { 166 3: OBJECT IDENTIFIER

       :             authorityKeyIdentifier (2 5 29 35)

171 24: OCTET STRING, encapsulates { 173 22: SEQUENCE { 175 20: [0]

       :                 08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E 70 6A
       :                 4A 20 84 2C 32
       :               }
       :             }
       :           }

197 10: SEQUENCE { 199 3: OBJECT IDENTIFIER cRLNumber (2 5 29 20) 204 3: OCTET STRING, encapsulates { 206 1: INTEGER 12

       :             }
       :           }
       :         }
       :       }
       :     }

209 13: SEQUENCE { 211 9: OBJECT IDENTIFIER

       :         sha1withRSAEncryption (1 2 840 113549 1 1 5)

222 0: NULL

       :     }

224 129: BIT STRING

       :     22 DC 18 7D F7 08 CE CC 75 D0 D0 6A 9B AD 10 F4
       :     76 23 B4 81 6E B5 6D BE 0E FB 15 14 6C C8 17 6D
       :     1F EE 90 17 A2 6F 60 E4 BD AA 8C 55 DE 8E 84 6F
       :     92 F8 9F 10 12 27 AF 4A D4 2F 85 E2 36 44 7D AA
       :     A3 4C 25 38 15 FF 00 FD 3E 7E EE 3D 26 12 EB D8
       :     E7 2B 62 E2 2B C3 46 80 EF 78 82 D1 15 C6 D0 9C
       :     72 6A CB CE 7A ED 67 99 8B 6E 70 81 7D 43 42 74
       :     C1 A6 AF C1 55 17 A2 33 4C D6 06 98 2B A4 FC 2E
       :   }

Cooper, et al. Standards Track [Page 149] RFC 5280 PKIX Certificate and CRL Profile May 2008

Authors' Addresses

 David Cooper
 National Institute of Standards and Technology
 100 Bureau Drive, Mail Stop 8930
 Gaithersburg, MD 20899-8930
 USA
 EMail: david.cooper@nist.gov
 Stefan Santesson
 Microsoft
 One Microsoft Way
 Redmond, WA 98052
 USA
 EMail: stefans@microsoft.com
 Stephen Farrell
 Distributed Systems Group
 Computer Science Department
 Trinity College Dublin
 Ireland
 EMail: stephen.farrell@cs.tcd.ie
 Sharon Boeyen
 Entrust
 1000 Innovation Drive
 Ottawa, Ontario
 Canada K2K 3E7
 EMail: sharon.boeyen@entrust.com
 Russell Housley
 Vigil Security, LLC
 918 Spring Knoll Drive
 Herndon, VA 20170
 USA
 EMail: housley@vigilsec.com
 Tim Polk
 National Institute of Standards and Technology
 100 Bureau Drive, Mail Stop 8930
 Gaithersburg, MD 20899-8930
 USA
 EMail: wpolk@nist.gov

Cooper, et al. Standards Track [Page 150] RFC 5280 PKIX Certificate and CRL Profile May 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights 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; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Cooper, et al. Standards Track [Page 151]

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