ISO/IEC 9594-6:2020/Amd 1:2025

Overview

ISO/IEC 9594-6:2020/Amd 1:2025 is Amendment 1 to Part 6 of the ISO/IEC 9594 series (ITU‑T Recommendation X.520). It updates the Directory’s set of selected attribute types and their ASN.1 representations to improve modularization of directory and cybersecurity ASN.1 modules. The amendment formalizes moves of many ASN.1 symbols from the SelectedAttributeTypes module into the UsefulDefinitions module (see Rec. ITU‑T X.501 | ISO/IEC 9594‑2), adds a normative reference to IETF RFC 4524 (COSINE LDAP/X.500 Schema), and introduces the DNS abbreviation.

Key topics

• ASN.1 module reorganization: Several attribute types, syntaxes and matching rules (for example, name, commonName, dnsName, objectIdentifier, PresentationAddress) are noted as relocated to the UsefulDefinitions module to support clearer separation between directory and cybersecurity ASN.1 artifacts.
• Matching rules and syntaxes: Notes highlight the relocation of matching rules such as caseIgnoreMatch, integerMatch, octetStringMatch, dnsNameMatch, and syntaxes like dnsString, directoryString, integer, oid, octetString, substringAssertion.
• Backward compatibility and documentation updates: Amendment adds NOTES throughout clauses and replaces Annex A with a revised SelectedAttributeTypes ASN.1 module text, while preserving the logical presence of moved symbols via imports.
• Standards coordination: Prepared by ITU‑T X.520 Amd.1 and coordinated with ISO/IEC JTC 1/SC 6, the amendment ensures alignment across ISO/IEC and ITU‑T directory specifications.
• Normative reference: RFC 4524 inclusion connects legacy COSINE LDAP/X.500 schema practices to the updated modular structure.

Applications

• Directory service implementers (LDAP/X.500): Use the updated ASN.1 modules and notes to implement compliant attribute type definitions and matching rules, improving interoperability and schema reuse.
• Identity and access management (IAM): Schema designers benefit from the modular separation when integrating directory attributes with cybersecurity modules (e.g., PKI or certificate-related schemas).
• Security architects and PKI vendors: Clear separation reduces accidental coupling between directory schema and security-specific ASN.1, simplifying audits and compliance.
• Standards authors and integrators: Provides authoritative guidance when mapping or migrating attribute definitions between modules or when referencing directory syntaxes and matching rules.

Related standards

• ISO/IEC 9594-2 (Rec. ITU‑T X.501) - UsefulDefinitions module (where many ASN.1 symbols now reside)
• ITU‑T X.520 - Recommendation corresponding to this amendment
• IETF RFC 4524 - COSINE LDAP/X.500 Schema (now a normative reference)

Keywords: ISO/IEC 9594-6 amendment, X.520, Selected attribute types, ASN.1 modules, directory schema, UsefulDefinitions, LDAP/X.500, RFC 4524, matching rules, directory syntaxes.