ISO/IEC 9594-8:2020

INTERNATIONAL ISO/IEC
STANDARD 9594-8
Ninth edition
2020-11
Information technology — Open
systems interconnection —
Part 8:
The Directory: Public-key and
attribute certificate frameworks
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
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ii © ISO/IEC 2020 – All rights reserved

Foreword
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This document was prepared by ITU-T as ITU-T X.509 (10/2019) and drafted in accordance with
its editorial rules, in collaboration with Joint Technical Committee ISO/IEC JTC 1, Information
technology, Subcommittee SC 6, Telecommunications and information exchange between systems.
This ninth edition cancels and replaces the eighth edition (ISO/IEC 9594-8:2017), which has been
technically revised.
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Any feedback or questions on this document should be directed to the user’s national standards body.
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© ISO/IEC 2020 – All rights reserved iii

CONTENTS
Page
SECTION 1 – General . 1
1 Scope . 1
2 Normative references. 1
2.1 Identical Recommendations | International Standards . 1
2.2 Paired Recommendations | International Standards equivalent in technical content . 2
2.3 Recommendations . 2
2.4 Other references . 2
3 Definitions . 3
3.1 OSI Reference Model security architecture definitions. 3
3.2 Baseline identity management terms and definitions . 3
3.3 Directory model definitions . 3
3.4 Access control framework definitions . 3
3.5 Public-key and attribute certificate definitions . 3
4 Abbreviations . 7
5 Conventions . 8
6 Frameworks overview . 8
6.1 Digital signatures . 9
6.2 Public-key cryptography and cryptographic algorithms. 10
6.3 Distinguished encoding of basic encoding rules . 12
6.4 Applying distinguished encoding . 12
6.5 Using repositories . 13
SECTION 2 – PUBLIC-KEY CERTIFICATE FRAMEWORK . 14
7 Public keys and public-key certificates . 14
7.1 Introduction . 14
7.2 Public-key certificate. 14
7.3 Public-key certificate extensions . 17
7.4 Types of public-key certificates . 18
7.5 Trust anchor . 18
7.6 Entity relationship . 19
7.7 Certification path . 19
7.8 Generation of key pairs . 21
7.9 Public-key certificate creation . 21
7.10 Certificate revocation list . 22
7.11 Uniqueness of names . 25
7.12 Indirect CRLs . 25
7.13 Repudiation of a digital signing . 26
8 Trust models . 27
8.1 Three-cornered trust model . 27
8.2 Four cornered trust model . 27
9 Public-key certificate and CRL extensions . 28
9.1 Policy handling . 29
9.2 Key and policy information extensions . 31
9.3 Subject and issuer information extensions . 38
9.4 Certification path constraint extensions . 41
9.5 Basic CRL extensions . 45
9.6 CRL distribution points and delta CRL extensions . 52
9.7 Authorization and validation list extensions . 57
9.8 Alternative cryptographic algorithms and digital signature extensions . 58
10 Delta CRL relationship to base . 59
11 Authorization and validation lists . 60
11.1 Authorization and validation list concept . 60
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Rec. ITU-T X.509 (10/2019) v
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11.2 The authorizer . 60
11.3 Authorization and validation list syntax . 61
11.4 Multiple cryptographic algorithms for authorization and validation list . 62
12 Certification path processing procedure . 63
12.1 Path processing inputs . 63
12.2 Path processing outputs . 63
12.3 Path processing variables . 64
12.4 Initialization step . 64
12.5 Public-key certificate processing . 65
13 PKI directory schema . 67
13.1 PKI directory object classes and name forms . 67
13.2 PKI directory attributes . 68
13.3 PKI directory matching rules . 72
13.4 PKI directory syntax definitions. 77
SECTION 3 – ATTRIBUTE CERTIFICATE FRAMEWORK . 80
14 Attribute certificates . 80
14.1 General . 80
14.2 Attribute certificate syntax . 81
14.3 Multiple cryptographic algorithms for attribute certificates . 83
14.4 Delegation paths . 83
14.5 Attribute certificate revocation lists . 84
15 Attribute authority, source of authority and certification authority relationship . 86
15.1 Privilege in attribute certificates . 87
15.2 Privilege in public-key certificates . 87
16 PMI models . 87
16.1 General model . 87
16.2 Control model. 89
16.3 Delegation model . 90
16.4 Group assignment model . 90
16.5 Roles model . 91
16.6 Recognition of Authority Model . 93
16.7 XML privilege information attribute . 96
16.8 Permission attribute and matching rule . 97
17 Attribute certificate and attribute certificate revocation list extensions . 97
17.1 Basic privilege management extensions . 98
17.2 Privilege revocation extensions . 101
17.3 Source of authority extensions . 107
17.4 Role extensions . 109
17.5 Delegation extensions . 110
17.6 Recognition of authority extensions . 114
17.7 Use of alternative digital signature algorithm and digital signature extensions . 117
18 Delegation path processing procedure . 118
18.1 Basic processing procedure . 118
18.2 Role processing procedure . 119
18.3 Delegation processing procedure . 119
19 PMI directory schema. 121
19.1 PMI directory object classes . 121
19.2 PMI directory attributes . 123
19.3 PMI general directory matching rules . 125
Annex A – Public-key and attribute certificate frameworks . 127
Annex B – Reference definition of cryptographic algorithms . 155
Annex C Certificate extension attribute types . 162
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vi Rec. ITU-T X.509 (10/2019)
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C.1 Certificate extension attribute concept . 162
C.2 Formal specification for certificate extension attribute types . 162
Annex D – External ASN.1 modules . 171
Annex E – CRL generation and processing rules . 180
E.1 Introduction . 180
E.2 Determine parameters for CRLs . 181
E.3 Determine CRLs required . 182
E.4 Obtain CRLs. 183
E.5 Process CRLs . 183
Annex F – Examples of delta CRL issuance. 187
Annex G – Privilege policy and privilege attribute definition examples . 189
G.1 Introduction . 189
G.2 Sample syntaxes . 189
G.3 Privilege attribute example . 193
2)
Annex H – An introduction to public key cryptography . 194
Annex I – Examples of use of certification path constraints . 196
I.1 Example 1: Use of basic constraints . 196
I.2 Example 2: Use of policy mapping and policy constraints . 196
I.3 Use of name constraints extension . 196
Annex J – Guidance on determining for which policies a certification path is valid . 205
J.1 Certification path valid for a user-specified policy required . 205
J.2 Certification path valid for any policy required . 206
J.3 Certification path valid regardless of policy . 206
J.4 Certification path valid for a user-specific policy desired, but not required . 206
Annex K – Key usage certificate extension issues . 207
Annex L – Deprecated extensions . 208
L.1 CRL scope extension . 208
Annex M – Directory concepts . 211
M.1 Scope . 211
M.2 The directory attribute concept. 211
M.3 Basic directory concepts . 211
M.4 Subtrees . 212
M.5 Directory distinguished names . 212
M.6 Directory schema . 213
Annex N – Considerations on strong authentication . 214
N.1 Introduction . 214
N.2 One-way authentication . 215
N.3 Two-way authentication . 215
N.4 Three-way authentication . 216
N.5 Five-way authentication (initiated by A) . 217
N.6 Five-way authentication (initiated by B) . 218
Annex O – Alphabetical list of information item definitions . 220
Annex P – Amendments and corrigenda . 223
Bibliography . 224
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Rec. ITU-T X.509 (10/2019) vii

Introduction
Many applications have requirements for security to protect against threats to the communication of information. Virtually
all security services are dependent upon the identities of the communicating parties being reliably known, i.e.,
authenticated.
This Recommendation | International Standard defines a framework for public-key certificates. This framework includes
the specification of data objects used to represent the public-key certificates themselves, as well as revocation notices for
issued public-key certificates that should no longer be trusted. It defines some critical components of a public-key
infrastructure (PKI), but it does not define a PKI in its entirety. However, this Recommendation | International Standard
provides the foundation upon which full PKIs and their specifications can be built.
Similarly, this Recommendation | International Standard defines a framework for attribute certificates. This framework
includes the specification of data objects used to represent the attribute certificates themselves, as well as revocation
notices for issued attribute certificates that should no longer be trusted. It defines some critical components of a privilege
management infrastructure (PMI), but it does not define a PMI in its entirety. However, this Recommendation |
International Standard provides the foundation upon which full PMIs and their specifications can be built.
Directory schema definitions allow PKI and PMI information to be represented in a directory according to the
specification found in the Directory Specifications (Rec. ITU-T X.500 | ISO/IEC 9594-1, Rec. ITU-T X.501 | ISO/IEC
9594-2, Rec. ITU-T X.511 | ISO/IEC 9594-3, Rec. ITU-T X.518 | ISO/IEC 9594-4, Rec. ITU-T X.519 | ISO/IEC 9594-5,
Rec. ITU-T X.520 | ISO/IEC 9594-6, Rec ITU-T X.521 | ISO/IEC 9594-7 and Rec. ITU-T X.525 | ISO/IEC 9594-9) or
according to the lightweight directory access protocol (LDAP) specification.
This Recommendation | International Standard provides the foundation frameworks upon which industry profiles can be
defined by other standards groups and industry forums. Many of the features defined as optional in these frameworks may
be mandated for use in certain environments through profiles. This ninth edition technically revises and enhances the
eighth edition of this Recommendation | International Standard.
This ninth edition specifies versions 1, 2 and 3 of public-key certificates, versions 1 and 2 of certificate revocation lists
and version 2 of attribute certificates.
The extensibility function was added in an earlier edition with version 3 of the public-key certificate and with version 2
of the certificate revocation list and was incorporated into the attribute certificate from its initial inception.
Annex A, which is an integral part of this Recommendation | International Standard, provides the ASN.1 modules which
contain all of the definitions associated with the frameworks.
Annex B, which is not an integral part of this Recommendation | International Standard, lists object identifiers assigned
to cryptographic algorithms defined by other specifications. It is provided for easy reference and import into other ASN.1
modules.
Annex C, which is an integral part of this Recommendation | International Standard, provides definitions for how
certificate extension types may be represented by directory attribute types.
Annex D, which is not an integral part of this Recommendation | International Standard, includes extracts of external
ASN.1 modules referenced by this Recommendation | International Standard.
Annex E, which is an integral part of this Recommendation | International Standard, provides rules for generating and
processing certificate revocation lists (CRLs).
Annex F, which is not an integral part of this Recommendation | International Standard, provides examples of delta
certificate revocation list (CRL) issuance.
Annex G, which is not an integral part of this Recommendation | International Standard, provides examples of privilege
policy syntaxes and privilege attributes.
Annex H, which is not an integral part of this Recommendation | International Standard, is an introduction to public-key
cryptography.
Annex I, which is not an integral part of this Recommendation | International Standard, contains examples of the use of
certification path constraints.
Annex J, which is not an integral part of this Recommendation | International Standard, provides guidance for public-key
infrastructure (PKI) enabled applications on the processing of certificate policy while in the certification path validation
process.
Annex K, which is not an integral part of this Recommendation | International Standard, provides guidance on the use of
the contentCommitment bit in the keyUsage certificate extension.
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viii Rec. ITU-T X.509 (10/2019)

Annex L, which is not an integral part of this Recommendation | International Standard, includes public-key and attribute
certificate extensions that have been deprecated.
Annex M, which is not an integral part of this Recommendation | International Standard, gives a short introduction to
directory and distinguished name concepts.
Annex N, which is not an integral part of this Recommendation | International Standard, provides some general
considerations on strong authentication.
Annex O, which is not an integral part of this Recommendation | International Standard, contains an alphabetical list of
information item definitions in this Recommendation | International Standard.
Annex P, which is not an integral part of this Recommendation | International Standard, lists the amendments and defect
reports that have been incorporated to form this edition of this Recommendation | International Standard.
© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.509 (10/2019) ix
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information technology – Open Systems Interconnection –
The Directory: Public-key and attribute certificate frameworks
SECTION 1 – GENERAL
1 Scope
This Recommendation | International Standard addresses some of the security requirements in the areas of authentication
and other security services through the provision of a set of frameworks upon which full services can be based.
Specifically, this Recommendation | International Standard defines frameworks for:
– public-key certificates; and
– attribute certificates.
The public-key certificate framework defined in this Recommendation | International Standard specifies the information
objects and data types for a public-key infrastructure (PKI), including public-key certificates, certificate revocation lists
(CRLs), trust broker and authorization and validation lists (AVLs). The attribute certificate framework specifies the
information objects and data types for a privilege management infrastructure (PMI), including attribute certificates, and
attribute certificate revocation lists (ACRLs). This Recommendation | International Standard also provides the framework
for issuing, managing, using and revoking certificates. An extensibility mechanism is included in the defined formats for
both certificate types and for all revocation list schemes. This Recommendation | International Standard also includes a
set of extensions, which is expected to be generally useful across a number of applications of PKI and PMI. The schema
components (including object classes, attribute types and matching rules) for storing PKI and PMI information in a
directory, are included in this Recommendation | International Standard.
This Recommendation | International Standard specifies the framework for strong authentication, involving credentials
formed using cryptographic techniques. It is not intended to establish this as a general framework for authentication, but
it can be of general use for applications which consider these techniques adequate.
Authentication (and other security services) can only be provided within the context of a defined security policy. It is a
matter for users of an application to define their own security policy.
2 Normative references
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition
of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
2.1 Identical Recommendations | International Standards
– Recommendation ITU-T X.411 (1999) | ISO/IEC 10021-4:2003, Information technology – Message
Handling Systems (MHS) – Message Transfer System: Abstract Service Definition and Procedures.
– Recommendation ITU-T X.500 (2019) | ISO/IEC 9594-1:2020, Information technology – Open Systems
Interconnection – The Directory: Overview of concepts, models and services.
– Recommendation ITU-T X.501 (2019) | ISO/IEC 9594-2:2020, Information technology – Open Systems
Interconnection – The Directory: Models.
– Recommendation ITU-T X.511 (2019) | ISO/IEC 9594-3:2020, Information technology – Open Systems
Interconnection – The Directory: Abstract service definition.
– Recommendation ITU-T X.518 (2019) | ISO/IEC 9594-4:2020, Information technology – Open Systems
Interconnection – The Directory: Procedures for distributed operation.
– Recommendation ITU-T X.519 (2019) | ISO/IEC 9594-5:2020, Information technology – Open Systems
Interconnection – The Directory: Protocol specifications.
© ISO/IEC 2020 – All rights reserved
Rec. ITU-T X.509 (10/2019) 1
– Recommendation ITU-T X.520 (2019) | ISO/IEC 9594-6:2020, Information technology – Open Systems
Interconnection – The Directory: Selected attribute types.
– Recommendation ITU-T X.521 (2019) | ISO/IEC 9594-7:2020, Information technology – Open Systems
Interconnection – The Directory: Selected object classes.
– Recommendation ITU-T X.525 (2019) | ISO/IEC 9594-9:2020, Information technology – Open Systems
Interconnection – The Directory: Replication.
– Recommendation ITU-T X.660 (2011) | ISO/IEC 9834-1:2012, Information technology – Open Systems
Interconnection – Procedures for the operation of OSI Registration Authorities: General procedures and
top arcs of the International Object Identifier tree.
– Recommendation ITU-T X.680 (2015) | ISO/IEC 8824-1:2015, Information technology – Abstract Syntax
Notation One (ASN.1): Specification of basic notation.
– Recommendation ITU-T X.681 (2015) | ISO/IEC 8824-2:2015, Information technology – Abstract Syntax
Notation One (ASN.1): Information object specification.
– Recommendation ITU-T X.682 (2015) | ISO/IEC 8824-3:2015, Information technology – Abstract Syntax
Notation One (ASN.1): Constraint specification.
– Recommendation ITU-T X.683 (2015) | ISO/IEC 8824-4:2015, Information technology – Abstract Syntax
Notation One (ASN.1): Parameterization of ASN.1 specifications.
– Recommendation ITU-T X.690 (2015) | ISO/IEC 8825-1:2015, Information technology – ASN.1 encoding
rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).
– Recommendation ITU-T X.812 (1995) | ISO/IEC 10181-3:1996, Information technology – Open Systems
Interconnection – Security frameworks for open systems: Access control framework.
– Recommendation ITU-T X.813 (1996) | ISO/IEC 10181-4:1997, Information technology – Open Systems
Interconnection – Security frameworks for open systems: Non-repudiation framework.
– Recommendation ITU-T X.841 (2000) | ISO/IEC 15816:2002, Information technology – Security
techniques – Security information objects for access control.
2.2 Paired Recommendations | International Standards equivalent in technical content
– Recommendation ITU-T X.800 (1991), Security architecture for Open Systems Interconnection for CCITT
applications.
ISO 7498-2:1989, Information processing systems – Open Systems Interconnection – Basic Reference
Model – Part 2: Security Architecture.
2.3 Recommendations
– Recommendation ITU-T X.1252 (2010), Baseline identity management terms and definitions.
2.4 Other references
– IETF RFC 791 (1981), Internet Protocol.
– IETF RFC 822 (1982), Standard for the Format of ARPA Internet Text Messages.
– IETF RFC 1630 (1994), Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of
Names and Addresses of Objects on the Network as used in the World-Wide Web.
– IETF RFC 3492 (2003), Punycode: A Bootstring encoding of Unicode for Internationalized Domain
Names in Applications (IDNA).
– IETF RFC 4511 (2006), Lightweight Directory Access Protocol (LDAP): The Protocol.
– IETF RFC 4523 (2006), Lightweight Directory Access Protocol (LDAP) Schema Definitions for X.509
Certificates.
– IETF RFC 5280 (2008), Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation
List (CRL) Profile.
– IETF RFC 5890 (2010), Internationalized Domain Names for Applications (IDNA): Definitions and
Document Framework.
– IETF RFC 5914 (2010), Trust Anchor Format.
© ISO/IEC 2020 – All rights reserved
2 Rec. ITU-T X.509 (10/2019)
– IETF RFC 6960 (2013), X.509 Internet Public Key Infrastructure Online Certificate Status Protocol –
OCSP.
3 Definitions
For the purposes of this Recommendation | International Standard, the following definitions apply.
3.1 OSI Reference Model security architecture definitions
The following terms are defined in Rec. ITU-T X.800 | ISO 7498-2:
a) authentication exchange;
b) authentication information;
c) confidentiality;
d) credentials;
e) cryptography;
f) data origin authentication;
g) decipherment;
h) digital signature;
i) encipherment; and
j) key;
3.2 Baseline identity management terms and definitions
The following term is defined in Rec. ITU-T X.1252:
a) trust.
3.3 Directory model definitions
The following terms are defined in Rec. ITU-T X.501 | ISO/IEC 9594-2:
a) attribute;
c) directory information tree (DIT);
b) directory system agent;
c) directory user agent (DUA);
d) distinguished name;
e) entry;
f) relative distinguished name;
g) root.
3.4 Access control framework definitions
The following terms are defined in Rec. ITU-T X.812 | ISO/IEC 10181-3:
a) access control decision function (ADF);
b) access control enforcement function (AEF).
3.5 Public-key and attribute certificate definitions
The following terms are defined in this Recommendation | International Standard:
3.5.1 ACRL distribution point: A directory entry or another distribution source for attribute certificate revocation
lists (ACRLs); an ACRL distributed through an ACRL distribution point may contain revocation entries for only a subset
of the full set of attribute certificates issued by one attribute authority (AA) or may contain revocation entries for multiple
AAs.
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Rec. ITU-T X.509 (10/2019) 3
3.5.2 attribute authority certificate: An attribute certificate for one attribute authority (AA) issued by another AA
or by the same AA.
3.5.3 attribute certificate: A data structure, digitally signed by an attribute authority that binds some attribute values
with identification information about its holder.
3.5.4 attribute authority (AA): An authority which assigns privileges by issuing attribute certificates or by including
them in public-key certificates.
3.5.5 attribute authority revocation list (AARL): A revocation list containing a list of references to attribute
certificates issued to attribute authorities (AAs) that are no longer considered valid by the issuing AA.
3.5.6 attribute certificate revocation list (ACRL): A revocation list containing a list of references to attribute
certificates that are no longer considered valid by the issuing attribute authority.
3.5.7 attribute certificate validation: The process of ensuring that an attribute certificate was valid at a given time,
including possibly the construction and processing of a delegation path, and ensuring that all attribute certificates in that
path were valid (e.g., were not expired or revoked) at that given time.
3.5.8 authority: An entity, responsible for the issuance of certificates or of revocation lists. Four types are defined in
this Recommendation | International Standard; a certification authority which issues public-key certificates, an attribute
authority which issues attribute certificates, a certificate revocation list (CRL) issuer which issues CRLs and an attribute
certificate revocation list (ACRL) issuer which issues ACRLs.
3.5.9 authorization and validation list (AVL): A signed list containing information to an AVL entity about potential
communications entities and possible restrictions on the communications with such entities.
3.5.10 authorization and validation list entity (AVL entity): An entity, when acting as a relying party, is dependent
on an AVL issued by a designated authorizer.
3.5.11 authorizer: An entity trusted by one or more entities operating as authorization and validation list (AVL)
entities to create, maintain and sign authorization and validation lists.
3.5.12 base attribute certificate revocation list (base ACRL): An attribute certificate revocation list (ACRL) that is
used as the foundation in the generation of a delta attribute certificate revocation list (dACRL).
3.5.13 base certificate revocation list (base CRL): A certificate revocation list (CRL) that is used as the foundation
in the generation of a delta certificate revocation list (dCRL).
3.5.14 CA certificate: A public-key certificate for one certification authority (CA) issued by another CA or by the
same CA.
3.5.15 certificate policy: A named set of rules that indicates the applicability of a public-key certificate to
...