ISO/IEC 9797-2:2021/Cor 1:2024

Overview

ISO/IEC 9797-2:2021/Cor 1:2024 is a technical corrigendum to ISO/IEC 9797-2:2021, the international standard that specifies message authentication code (MAC) mechanisms based on a dedicated hash-function. This Corrigendum 1 corrects and clarifies algorithm descriptions, notation, constant definitions and implementation details (for example, key processing, constant strings for dedicated hash‑functions, and sponge/KECCAK-related rates). It is intended for implementers and evaluators of MAC algorithms who follow the ISO/IEC 9797 series for message integrity and authentication.

Key Topics and Requirements

• Clarified mathematical notation: use of the ceiling function (⌈x⌉) is explicitly added to Clause 4.
• Key expansion/padding: If K is shorter than 128 bits, concatenate K to itself ⌈128/k⌉ times and select the leftmost 128 bits to form the 128‑bit key K′.
• Key partitioning: Updated representation of a 128‑bit key as K = K0 ∥ K1 ∥ … ∥ K7 (eight 16‑bit or byte-aligned subblocks as defined in the standard).
• Dedicated hash-function constants: Corrections to the 128‑bit constant strings T_i for dedicated hash-functions 4, 5, 6, 8, etc.
• KECCAK / KMAC notes: Corrections clarify SPONGE parameter rates (e.g., numbers 168 and 136 as byte rates corresponding to SPONGE[f, pad, 1344] and SPONGE[f, pad, 1088]) and how KMAC behaves as an XOF (encoded output length = 0).
• MAC lengths: Updates to the specified MAC output lengths m for various dedicated hash-functions (examples: m = 128 for functions 4, 12, 14, 17; m = 192 for functions 6 and 15; etc.).
• Annex and bibliography edits: Text updates in Annex C (security assumption wording) and removal of a bibliography entry.

Practical Applications

• Secure message integrity and authentication for network protocols, APIs, payment systems, embedded/IoT devices, firmware updates, and secure logging.
• Implementations that require conformance to ISO/IEC standards for certification, interoperability, or regulatory compliance.
• Cryptographic libraries, hardware security modules (HSMs), and firmware developers implementing dedicated-hash MAC algorithms and KMAC/KECCAK modes.

Who Should Use This Standard

• Cryptographic engineers and protocol designers implementing or evaluating MAC schemes.
• Software and hardware implementers seeking ISO/IEC 9797 compliance.
• Security auditors, certification bodies, and standards teams validating MAC algorithm behavior and constants.
• Product teams in finance, telecommunications, and IoT requiring standardized message authentication.

Related Standards and Keywords

• Part of the ISO/IEC 9797 series (Message Authentication Codes). Corrigendum addresses dedicated-hash mechanisms and interoperability details involving KECCAK, KMAC, SPONGE constructions, 128-bit key handling, and MAC output lengths. Keywords: ISO/IEC 9797-2, message authentication code, MAC, dedicated hash-function, KECCAK, KMAC, SPONGE, technical corrigendum, key padding, MAC length.