ISO/IEC 9798-2:2019

Overview

ISO/IEC 9798-2:2019 - "IT Security techniques - Entity authentication - Part 2: Mechanisms using authenticated encryption" specifies standardized entity authentication mechanisms that use authenticated encryption algorithms. The standard defines six mechanisms: four that operate without an on-line trusted third party (two for unilateral authentication and two for mutual authentication) and two that require an on-line trusted third party (TTP) to establish common secret keys. Annex A of the standard provides Object Identifiers (OIDs) for the mechanisms.

Key topics and requirements

• Authenticated encryption: Mechanisms rely on authenticated encryption to provide confidentiality, integrity and data origin authentication-ensuring decrypted tokens are unforgeable.
• Mechanism types: Named mechanisms include UNI.TS, UNI.CR (unilateral) and MUT.TS, MUT.CR (mutual), plus TP.TS and TP.CR which involve a TTP.
• Time-variant parameters: Use of random numbers (nonces), time-stamps, or sequence numbers to prevent replay; verification rules depend on the parameter type.
• Secret authentication keys: Claimant and verifier must share a secret key (or share keys with a TTP). Keys must be unique to authentication use, protected, and have appropriate lifetimes to avoid cryptanalysis.
• Token structure & SID constants: Encrypted tokens must include mechanism/instance identifiers (SID) so strings cannot be interchanged or replayed across contexts.
• Unforgeability & integrity: For every key, the authenticated-decryption function must allow detection of forged or manipulated data-only legitimate key holders can create acceptable tokens.
• Protocol pass counts: Number of message passes varies by method - e.g., one-pass possible for some unilateral timestamp methods, two/three passes needed for other challenge–response or mutual cases; TTP involvement adds additional exchanges.
• Operational requirements: If a TTP is used it must be mutually trusted; key management practices (ISO/IEC 11770-1/-2 guidance) are necessary.

Applications and who uses it

• Implementers of secure authentication protocols in enterprise systems, embedded devices, and IoT.
• Security architects and protocol designers selecting authenticated-encryption–based authentication for APIs, network services, and device onboarding.
• Vendors of cryptographic libraries and secure modules that need standards-compliant authentication primitives.
• Organisations requiring interoperable authentication with clear Object Identifiers for mechanism identification and conformance testing.
• Compliance officers and auditors evaluating authentication schemes against international best practices.

Related standards

• ISO/IEC 9798-1 (Entity authentication - General)
• ISO/IEC 19772 (Authenticated encryption guidance)
• ISO/IEC 11770-1, -2 (Key management)
• ISO/IEC 18031 (Random number guidance)
• ISO/IEC 8825-1 (Encoding rules referenced for concatenation)

ISO/IEC 9798-2:2019 is essential when you need standardized, authenticated-encryption–based entity authentication that protects against replay and forgery while supporting both TTP-based and direct shared-key scenarios.