ISO/IEC 9594-11:2025

Information technology - Open systems interconnection directory - Part 11: Protocol specifications for secure operations

This document provides guidance on how to prepare new and old protocols for cryptographic algorithm migration and defines auxiliary cryptographic algorithms to be used for migration purposes. This document specifies a general wrapper protocol that provides authentication, integrity and confidentiality (encryption) protection for other protocols. This wrapper protocol includes a migration path for cryptographic algorithms allowing for smooth migration to stronger cryptographic algorithms as such requirements evolve. This will allow migration to quantum-safe cryptographic algorithms. Protected protocols can then be developed without taking security and cryptographic algorithms into consideration. This document also includes some protocols to be protected by the wrapper protocol primarily for support of public-key infrastructure (PKI). Other specifications, e.g., Recommendations or International Standards, may also develop protocols designed to be protected by the wrapper protocol.

Technologies de l'information — Interconnexion de systèmes ouverts (OSI) — Partie 11: Titre manque

General Information

• Status: Published
• Publication Date: 26-Aug-2025
• ICS: 35.100.70 - Application layer
• Technical Committee: ISO/IEC JTC 1/SC 6 - Telecommunications and information exchange between systems
• Drafting Committee: ISO/IEC JTC 1/SC 6/WG 10 - Directory, ASN.1 and Registration
• Current Stage: 6060 - International Standard published
• Start Date: 27-Aug-2025
• Due Date: 22-Feb-2028
• Completion Date: 27-Aug-2025

Relations

• Revises: ISO/IEC 9594-11:2020 - Information technology - Open systems interconnection directory - Part 11: Protocol specifications for secure operations
• Effective Date: 01-Mar-2025

Overview - ISO/IEC 9594-11:2025 (Directory - Protocol specifications for secure operations)

ISO/IEC 9594-11:2025 defines a standardized approach to securing Open Systems Interconnection (OSI) directory protocols by specifying a general wrapper protocol that provides authentication, integrity and confidentiality for other protocols. The standard focuses on enabling smooth cryptographic algorithm migration (including migration to quantum‑safe algorithms) so protected protocols can be developed without embedding specific cryptographic algorithms. This second edition (prepared as ITU‑T X.510) replaces the 2020 edition and updates protocol, cryptographic and key‑management guidance for directory services and PKI-related operations.

Key technical topics and requirements

• Wrapper protocol architecture

  • General concepts, communication model, data unit structure and error handling for the wrapper that encapsulates protected protocols.
  • Association (handshake), data transfer and release procedures; sequence numbers; invocation identifiers.

• Cryptographic algorithm migration

  • Guidance and auxiliary algorithm specifications to support migration paths and coexistence of old and new algorithms.
  • Mechanisms to allow switching to stronger / quantum‑safe algorithms without redesigning protected protocols.

• Cryptographic primitives and key management

  • Specification of symmetric algorithms (e.g., AES, Camellia, SEED, SM4).
  • Public‑key and digital signature algorithm coverage and key establishment methods including Diffie‑Hellman (prime field) and Elliptic Curve Diffie‑Hellman (ECDH).
  • Key derivation, symmetric key renewal and sequence number usage.

• Protected protocols (examples)

  • Protocols for Public Key Infrastructure (PKI) support such as certification authority subscription and authorization/validation list management.
  • Plug‑in model for other standards to be secured by the wrapper protocol.

• Data types, ASN.1 tooling and multiple‑algorithm specification

  • Use of ASN.1 information object class tools and parameterized data types to express multi‑algorithm values and algorithm identifiers.

Practical applications and who uses this standard

• Directory service implementers and vendors securing LDAP/OSI directory interactions.
• PKI operators and Certification Authorities implementing subscription, certificate distribution and validation management.
• Security architects designing protocol stacks that must remain algorithm‑agile and future‑proof against quantum threats.
• Product teams building secure middleware, gateways or appliances that need a standard wrapper to protect diverse application protocols.
• Standards bodies and specification authors who want their protocols to be interoperable with a standardized, algorithm‑migratable security layer.

Related standards and references

• ISO/IEC 9594 series (Directory standards)
• ITU‑T Recommendation X.510 (basis for this edition)
• Relevant cryptographic algorithm standards (e.g., AES) and future quantum‑safe algorithm specifications

Keywords: ISO/IEC 9594-11:2025, wrapper protocol, cryptographic algorithm migration, quantum‑safe, directory, PKI, ASN.1, Diffie‑Hellman, AES, secure operations.

Standards Content (Sample)

International
Standard
ISO/IEC 9594-11
Second edition
Information technology —
2025-08
Open systems interconnection
directory —
Part 11:
Protocol specifications for secure
operations
Reference number
© ISO/IEC 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
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ISO copyright office
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Published in Switzerland
© ISO/IEC 2025 – All rights reserved
ii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members
of ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
document should be noted.
ISO and IEC draw attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held responsible for
identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by ITU-T as ITU-T X.510 (10/2023) 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 second edition cancels and replaces the first edition (ISO/IEC 9594-11:2020), which has been technically
revised.
A list of all parts in the ISO/IEC 9594 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html and www.iec.ch/national-
committees.
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 . 1
2.3 International Standards . 2
2.4 Other references . 2
3 Definitions . 2
3.1 OSI reference model definitions . 2
3.2 Directory model definitions . 2
3.3 Public-key and attribute certificate definitions . 2
3.4 Terms defined in this Recommendation | International Standard . 3
4 Abbreviations . 4
5 Conventions . 5
6 Communication model . 5
7 Common data types and special cryptographic algorithms . 5
7.1 Introduction . 5
7.2 ASN.1 information object class specification tool. 5
7.3 Parameterized data types . 7
7.4 Multiple cryptographic algorithm specifications . 9
7.5 Parameterized data types for providing multiple-cryptographic algorithm-values . 15
7.6 Formal specification of encipherment . 16
8 Symmetric-key algorithms . 17
8.1 Introduction to symmetric-key algorithms . 17
8.2 Advance encryption standard (AES) – symmetric-key algorithms . 18
8.3 Camellia symmetric-key algorithms . 21
8.4 SEED – symmetric-key algorithms . 24
8.5 SM4 – symmetric-key algorithms. 26
9 Public-key and digital signature algorithms . 28
10 Key establishment algorithms . 28
10.1 General . 28
10.2 Diffie-Hellman over prime field . 28
10.3 Elliptic curve Diffie-Hellman . 30
10.4 Key derivation . 31
11 General concepts for securing protocols . 32
11.1 Introduction . 32
11.2 Protected protocol plug-in concept . 32
11.3 Communication structure . 32
11.4 Another view of the relationship between the wrapper protocol and the protected protocol . 33
11.5 Structure of the application protocol data unit . 33
11.6 Exception conditions . 33
SECTION 2 – THE WRAPPER PROTOCOL . 34
12 Wrapper protocol general concepts . 34
12.1 Introduction . 34
12.2 UTC time specification . 34
12.3 Use of alternative cryptographic algorithms . 34
12.4 Establishment of symmetric keys . 34
12.5 Sequence numbers . 35
12.6 Use of invocation identification in the wrapper protocol . 35
12.7 Mapping to underlying services . 35
12.8 Addressing of communicating entities. 35
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
iv
12.9 Definition of protected protocols . 35
12.10 Overview of wrapper protocol data units. 35
13 Association management . 36
13.1 Introduction to association management . 36
13.2 Association handshake request . 36
13.3 Association handshake accept . 37
13.4 Association reject due to security issues . 38
13.5 Association reject by the protected protocol . 39
13.6 Handshake security abort . 40
13.7 Handshake abort by protected protocol . 40
13.8 Data transfer security abort . 41
13.9 Abort by protected protocol . 41
13.10 Release request WrPDU . 42
13.11 Release response WrPDU . 42
13.12 Release collision . 43
14 Data transfer phase . 43
14.1 Symmetric keys renewal . 43
14.2 Data transfer by the client . 44
14.3 Data transfer by the server . 45
15 Information flow. 48
15.1 Purpose and general model . 48
15.2 Protected protocol SAOC . 49
15.3 Wrapper SAOC . 49
16 Wrapper error handling . 52
16.1 General . 52
16.2 Checking of a wrapper handshake request . 52
16.3 Checking of a wrapper handshake accept . 53
16.4 Checking of data transfer WrPDUs . 54
16.5 Wrapper diagnostic codes . 56
17 End-to-end communications . 57
SECTION 3 – PROTECTED PROTOCOLS . 58
18 Authorization and validation list management . 58
18.1 General on authorization and validation management . 58
18.2 Defined protected protocol data unit types . 58
18.3 Authorization and validation management protocol initialization request . 59
18.4 Authorization and validation management protocol initialization accept . 59
18.5 Authorization and validation management protocol initialization reject . 59
18.6 Authorization and validation management protocol initialization abort . 59
18.7 Add authorization and validation list request . 60
18.8 Add authorization and validation list response . 61
18.9 Replace authorization and validation list request . 61
18.10 Replace authorization and validation list response . 61
18.11 Delete authorization and validation list request . 62
18.12 Delete authorization and validation list response . 62
18.13 Authorization and validation list abort . 63
18.14 Authorization and validation list error codes . 63
19 Certification authority subscription protocol . 64
19.1 Certification authority subscription introduction . 64
19.2 Defined protected protocol data unit types . 64
19.3 Certification authority subscription protocol initialization request. 65
19.4 Certification authority subscription protocol initialization accept . 65
19.5 Certification authority subscription protocol initialization reject . 65
19.6 Certification authority subscription protocol initialization abort . 65
19.7 Public-key certificate subscription request . 66
19.8 Public-key certificate subscription response . 66
19.9 Public-key certificate un-subscription request . 67
19.10 Public-key certificate un-subscription response . 68
19.11 Public-key certificate replacements request . 69
19.12 Public-key certificate replacement response . 69
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
v
19.13 End-entity public-key certificate updates request . 70
19.14 End-entity public-key certificate updates response . 71
19.15 Certification authority subscription abort . 72
19.16 Certification authority subscription error codes. 72
20 Trust broker protocol . 72
20.1 Introduction . 72
20.2 Defined protected protocol data unit types . 73
20.3 Trust broker protocol initialization request . 73
20.4 Trust broker protocol initialization accept . 73
20.5 Trust broker protocol initialization reject . 73
20.6 Trust broker protocol initialization abort . 74
20.7 Trust broker request syntax . 74
20.8 Trust broker response syntax . 74
20.9 Trust broker error information . 75
Annex A Crypto Tools in ASN.1 . 76
Annex B General cryptographic algorithms . 81
Annex C Wrapper protocol in ASN.1 . 92
Annex D Protected protocol interface to the wrapper protocol . 97
Annex E Authorization and validation list management in ASN.1 . 99
Annex F Certification authority subscription in ASN.1. 102
Annex G Trust broker in ASN.1 . 106
Annex H Migration of cryptographic algorithms . 108
H.1 Migration of cryptographic algorithms . 108
H.2 Migration tools or migration approaches . 109
H.3 Migration of public-key certificates and other data types using the extension mechanism . 110
H.4 General migration approach for communication protocols . 110
H.5 Use of multiple and choice cryptographic algorithms . 111
Annex I Auxiliary specifications . 114
Annex J Amendments and corrigenda . 119
Bibliography . 120
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
vi
Introduction
The Internet Engineering Task Force (IETF) maintains a substantial set of protocols for supporting public-key
infrastructure (PKI). Recommendation ITU-T X.510 | ISO/IEC 9594-11 provides protocols to supplement those protocols
developed by IETF, especially for:
a) supporting new functions specified by Rec. ITU-T X.509 | ISO/IEC 9594-8, for which IETF has not
provided support, e.g., support for authorization and validation list (AVL) maintenance;
b) constraint environments, where lean protocols are required.
In addition, it specifies:
c) a wrapper protocol that provides security services for other protocols.
This Recommendation | International Standard consist of three sections as follows.
Section 1 gives general specifications for this Recommendation | International Standard.
Section 2 is the wrapper protocol specification.
Section 3 specifies some protocols to be protected by the wrapper protocol:
a) a protocol for maintaining authorization and validation lists (AVLs);
b) a protocol for subscribing public-key certificate status information from certification authorities (CAs);
and
c) a protocol for accessing a trust broker.
The following annexes are included:
Annex A, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for
specifications to be imported by protocols providing a migration path for cryptographic algorithms.
Annex B, which is an integral part of this Recommendation | International Standard, provides cryptographic algorithm
specification.
Annex C, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for the
wrapper protocol.
Annex D, which is an integral part of this Recommendation | International Standard, provides specifications for how a
protected protocol is wrapped by the wrapper protocol.
Annex E, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for
maintenance of the authorization and validation lists (AVLs) protocol.
Annex F, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for
certification authority subscription protocol.
Annex G, which is an integral part of this Recommendation | International Standard, provides the ASN.1 module for the
trust broker protocol.
Annex H, which is not an integral part of this Recommendation | International Standard, provides guidance for
cryptographic algorithm migration.
Annex I, which is not an integral part of this Recommendation | International Standard, reproduces the ASN.1
specification from other Specifications in the Rec. ITU X.500 Series | ISO/IEC 9594-all parts.
Annex J, which is not an integral part of this Recommendation | International Standard, provides lists amendments and
corrigenda included in this Specification.
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
vii
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information Technology – Open systems Interconnection – The Directory – Protocol
specifications for secure operations
SECTION 1 – GENERAL
1 Scope
This Recommendation | International Standard provides guidance on how to prepare new and old protocols for
cryptographic algorithm migration and defines auxiliary cryptographic algorithms to be used for migration purposes.
This Recommendation | International Standard specifies a general wrapper protocol that provides authentication, integrity
and confidentiality (encryption) protection for other protocols. This wrapper protocol includes a migration path for
cryptographic algorithms allowing for smooth migration to stronger cryptographic algorithms as such requirements
evolve. This will allow migration to quantum-safe cryptographic algorithms. Protected protocols can then be developed
without taking security and cryptographic algorithms into consideration.
This Recommendation | International Standard also includes some protocols to be protected by the wrapper protocol
primarily for support of public-key infrastructure (PKI). Other specifications, e.g., Recommendations or International
Standards, may also develop protocols designed to be protected by the wrapper protocol.
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.501 (2019) | ISO/IEC 9594-2:2020, Information technology – Open Systems
Interconnection – The Directory: Models.
– Recommendation ITU-T X.509 (2019) | ISO/IEC 9594-8:2020, Information technology – Open Systems
Interconnection – The Directory: Public-key and attribute certificate frameworks.
– Recommendation ITU-T X.680 (2021) | ISO/IEC 8824-1:2021, Information technology - Abstract Syntax
Notation One (ASN.1): Specification of basic notation.
– Recommendation ITU-T X.681 (2021) | ISO/IEC 8824-2:2021, Information technology – Abstract Syntax
Notation One (ASN.1): Information object specification.
– Recommendation ITU-T X.682 (2021) | ISO/IEC 8824-3:2021, Information technology - Abstract Syntax
Notation One (ASN.1): Constraint specification.
– Recommendation ITU-T X.683 (2021) | ISO/IEC 8824-4:2021, Information technology - Abstract Syntax
Notation One (ASN.1): Parameterization of ASN.1 specifications.
– Recommendation ITU-T X.690 (2021) | ISO/IEC 8825-1:2021, 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.691 (2021) | ISO/IEC 8825-2:2021, Information technology – ASN.1 encoding
rules: Specification of Packed Encoding Rules (PER).
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.
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
2.3 International Standards
– ISO/IEC 10116:2017, Information technology – Security techniques – Modes of operation for a n-bit block
cipher.
– ISO/IEC 18033-3:2010, Information technology – Security techniques – Encryption algorithms – Part 3:
Block ciphers.
– ISO/IEC 18033-3:2010/Amd.1:2021, Information technology – Security techniques – Encryption
algorithms – Part 3: Block ciphers, Amendment 1: SM4.
2.4 Other references
– IETF RFC 793 (1981), Transmission Control Protocol.
– IETF RFC 2104 (1997), HMAC: Keyed-Hashing for Message Authentication.
– IETF RFC 3526 (2003), More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key
Exchange (IKE).
– IETF RFC 5084 (2007), Using AES-CCM and AES-GCM Authenticated Encryption in the Cryptographic
Message Syntax (CMS).
– IETF RFC 5114 (2008), Additional Diffie-Hellman Groups for Use with IETF Standards.
– IETF RFC 5869 (2010), HMAC-based Extract-and-Expand Key Derivation Function (HKDF).
– IETF RFC 6932 (2013), Brainpool Elliptic Curves for the Internet Key Exchange (IKE) Group Description
Registry.
3 Definitions
For the purposes of this Recommendation | International Standard, the following definitions apply:
3.1 OSI reference model definitions
The following terms are defined in Rec. ITU-T X.800 | ISO 7498-2:
a) confidentiality;
b) cryptography;
c) digital signature.
3.2 Directory model definitions
The following term is defined in Rec. ITU-T X.501 | ISO/IEC 9594-2:
a) attribute.
3.3 Public-key and attribute certificate definitions
The following terms are defined in Rec. ITU-T X.509 | ISO/IEC 9594-8:
a) attribute certificate;
b) authorization and validation list (AVL);
c) authorization and validation list entity (AVL entity);
d) authorizer;
e) certification authority (CA);
f) certification path;
g) end entity;
h) end-entity public-key certificate;
i) hash function;
j) key agreement;
k) private key;
l) public key;
m) public-key certificate;
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
n) public-key infrastructure (PKI);
o) relying party.
3.4 Terms defined in this Recommendation | International Standard
This Recommendation | International Standard defines the following terms:
3.4.1 abstract syntax: A specification of application-protocol-data-units by using notation rules that are independent
of the encoding technique used to represent them.
NOTE – The term abstract syntax is originally an OSI term but is extended here to be general applicable.
3.4.2 alternative cryptographic algorithm: A cryptographic algorithm to which migration is wanted.
3.4.3 application entity: An active element embodying a set of capabilities which is pertinent to communication
systems, and which is defined for the application layer.
NOTE – The term application entity is originally an open systems interconnection (OSI) term, but is extended here to be generally
applicable.
3.4.4 application protocol data unit (APDU): Data that is transmitted as a single unit at the application layer
between two application entities.
3.4.5 association: A cooperative relationship between two application entities, which enables the communication of
information and the coordination of their joint operation for an instance of communication.
3.4.6 block: A string of bits of defined length.
3.4.7 block cipher: Symmetric encipherment system with the property that the encryption algorithm operates on a
block of plain text, i.e., a string of bits of a defined length, to yield a block of ciphertext.
3.4.8 client: The entity that initiates an association.
3.4.9 cryptographic algorithm pluck-in concept: The ability to specify the use of a cryptographic algorithm in the
base protocol, but the exact selection of the cryptographic algorithm is determined later for a particular instance of
communication.
3.4.10 cryptographic check algorithm: Either an integrity check value (ICV) algorithm or a digital signature
algorithm, i.e., an algorithm that takes as an input a message and a symmetric or private key and returns a string of bits
that can be used to verify the origin and integrity of the message.
3.4.11 cryptographic check value: Output of a cryptographic check function invocation.
3.4.12 data transfer phase: The phase from the completion of the establishment of an association to the termination
of the association.
3.4.13 digital signature: The result of a cryptographic transformation of data that, when properly implemented,
provides a mechanism for origin authentication, data integrity and signatory non-repudiation.
3.4.14 inner cryptographic algorithm: A cryptographic algorithm that included as a parameter of an outer
cryptographic algorithm.
3.4.15 native cryptographic algorithm: A cryptographic algorithm used prior to a migration period.
3.4.16 protected protocol data unit (PrPDU): Application protocol data unit defined by an application protocol to
be protected by the wrapper protocol.
3.4.17 protected protocol pluck-in concept: The ability to specify the inclusion of a communications protocol to be
protected in the base protocol, but the exact identification of a specific protocol is determined later for a particular instance
of communication.
3.4.18 outer cryptographic algorithm: A cryptographic algorithm that has as parameters one or more other
cryptographic algorithms, and in this way lets multiple inner cryptographic algorithms have the appearance of a single
cryptographic algorithm.
3.4.19 server: The entity that accepts or rejects an association request.
3.4.20 symmetric key: A cryptographic key used for both encryption of plaintext and decryption of ciphertext.
3.4.21 wrapper protocol data unit (WrPDU): An application protocol data unit carrying security protocol control
information and, when relevant, carrying a protected protocol data unit.
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
4 Abbreviations
For the purposes of this Recommendation | International Standard, the following abbreviations apply:
AEAD Authenticated Encryption with Associated Data
AES Advanced Encryption Standard
APDU Application Protocol Data Unit
ASN.1 Abstract Syntax Notation One
AVL Authorization and Validation List
AVMP Authorization and Validation Management Protocol
BER Basic Encoding Rules
CA Certification Authority
CAM CAMELLIA
CASP Certification Authority Subscription Protocol
CBC Cipher Block Chaining
CFB Cipher FeedBack
CMAC Cipher-based Message Authentication Code
CTR Counter
DER Distinguished Encoding Rules
DH Diffie-Hellman
DNS Domain Name System
ECB Electronic CodeBook
ECDH Elliptic Curve Diffie-Hellman
FQDN Fully Qualified Domain Name
HKDF HMAC-based extract-and-expand Key Derivation Function
HMAC keyed-Hash Message Authentication Code
ICV Integrity Check Value
ICT Information and Communications Technology
ID Identifier
LoA Loss of Alignment
MAC Message Authentication Code
MODP Modular exponential
OFB Output Feedback
OKM Output Keying Material
OSI Open Systems Interconnection
PDU Protocol Data Unit
PKI Public-Key Infrastructure
PMI Privilege Management Infrastructure
PRK Pseudorandom Key
PrPDU Protected protocol Data Unit
RAOC Receive Application Object Class
SAOC Send Application Object Class
SIV  Synthetic Initialization Vector
TCP Transmission Control Protocol
UTC Coordinated Universal Time
WrPDU Wrapper Protocol Data Unit
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
5 Conventions
The term "Specification" (as in "this Specification") shall be taken to mean this Recommendation | International Standard.
If an International Standard or ITU-T Recommendation is referenced within normal text without an indication of the
edition, the edition shall be taken to be the one specified in the normative references clause.
This Specification makes extensive use of the abstract syntax notation one (ASN.1) for the formal specification of data
types and values, as it is specified in Rec. ITU-T X.680 | ISO/IEC 8824-1, Rec. ITU-T X.681 | ISO/IEC 8824-2,
Rec. ITU-T X.682 | ISO/IEC 8824-3, Rec. ITU-T X.683 | ISO/IEC 8824-4, Rec. ITU-T X.690 | ISO/IEC 8825-1 and
Rec. ITU-T X.691 | ISO/IEC 8825-2.
This Specification presents ASN.1 notation in the bold Courier New typeface. When ASN.1 types and values are
referenced in normal text, they are differentiated from normal text by presenting them in the bold Courier New
typeface.
6 Communication model
Figure 1 illustrates the Internet communication model and its relationship to the OSI reference model. The communication
model illustrates that an entity communicates with another entity at different layers.
Figure 1 – Communication model
7 Common data types and special cryptographic algorithms
7.1 Introduction
This clause defines some auxiliary cryptographic specification as follows:
a) ASN.1 information object classes are heavily used for protocol design. The ALGORITHM information object
class is important for this Specification. This is further expanded in clause 7.2.
b) Multiple cryptographic algorithms of a specific class may be specified by using a single containing
cryptographic algorithm. This is done by utilizing the flexibility provided by the AlgorithmIdentifier
parameterized data type defined in clause 6.2.2 of Rec. ITU-T X.509 | ISO/IEC 9594-8. This is further
described in clause 7.3.
c) Some parameterized data types are defined in clause 7.3 for flexible protocol design.
d) Some formal specifications for encipherment are given in clause 7.6.
7.2 ASN.1 information object class specification tool
7.2.1 General information object class concept
The concept of ASN.1 information object class is specified in Rec. ITU-T X.681 | ISO/IEC 8824-2. It is, together with
the parameterized data type concept, vital for protocol design. For that reason, a short introduction is included here to
encourage increased use of this facility. ASN.1 information object classes are widely used by the ITU-T X.500 series of
Rec. ITU-T X.510 (10/2023)
© ISO/IEC 2025 – All rights reserved
Recommendations | ISO/IEC 9594-all parts for defining attribute types, matching rules, extensions to public-key and
attribute certificates, etc.
Figure 2 illustrates the general ASN.1 information object class concept. An ASN.1 information object class specifies the
general syntax for a class of information objects, e.g., attribute types as defined by Rec. ITU-T X.501 | ISO/IEC 9594-2.
From this general specification, specifications for specific attribute types may be derived, e.g., an attribute type for e-mail
addresses. From this general e-mail specification, instances of e-mail address attributes may be generated. Instances are
what is transferred in protocols or stored in a database (directory).
NOTE – The concept of object classes used in clause 15 is somewhat different from the concept of information object class
described above and defined in Rec. ITU-T X.681 | ISO/IEC 8824-2.
Figure 2 – ASN.1 information object class concept
7.2.2 The ALGORITHM information object class
The information object class concept is used to define cryptographic algorithms. The ALGORITHM information object class
is defined in clause 6.2.2 of Rec. ITU-T X.509 | ISO/IEC 9594-8. The specification of this information object class is
reproduced below for easy reference. The ALGORITHM information object class is different from most other information
object classes in the sense that an instance of an information object is an invocation of the algorithm rather than specifying
a value identifying something, like an e-mail address.
The following ASN.1 information object class is used for specifying cryptographic algorithms.
ALGORITHM ::= CLASS {
&Type OPTIONAL,
&DynParms OPTIONAL,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
[PARMS &Type]
[DYN-PARMS &DynParms ]
IDENTIFIED BY &id }
The ALGORITHM information object class has the following fields:
a) The &Type field is used to specify those fixed parameters that are necessary for specifying the exact
procedure for implementation of the cryptographic algorithm being defined. Not all cryptographic
algorithms require such parameters. The field is then absent or has the value NULL, as determined by the
individual cryptographic algorithm specifications. This field may take data of any syntax.
b) The &DynParms field is used to specify those dynamic parameters that determine the value(s) to be
exchanged between two communicating entities when invoking the cryptographic algorithm. Not all
cryptographic algorithms require dynamic parameters. In this case the &DynParms field shall be absent.
This field may take data of any syntax.
c) The &id field is used to uniquely identify the class of cryptographic algorithm being defined using a unique
object identifier.
The ALGORITHM information object class defined in Rec. ITU-T X.509 (2016) | ISO/IEC 9594-8:2017 for cryptographic
algorithms did not make a distinction between cryptographic algorithm between fixed and dynamic parameters. The
ALGORITHM information object class has therefore been extended in Rec. ITU-T X.509 (2019) | ISO/IEC 9594-6:202
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