ISO/IEC 18033-3:2010

Overview

ISO/IEC 18033-3:2010 - "Information technology - Security techniques - Encryption algorithms - Part 3: Block ciphers" is the international standard that specifies a set of block cipher algorithms for the protection of data confidentiality. The document defines how symmetric block ciphers map fixed-size plaintext blocks to ciphertext blocks under a key, and it standardizes seven specific algorithms across two block sizes (64-bit and 128-bit).

Key algorithms covered:

• 64-bit block ciphers: TDEA, MISTY1, CAST-128, HIGHT
• 128-bit block ciphers: AES, Camellia, SEED

The standard includes algorithm descriptions, encryption/decryption operations, functions, key schedules, test vectors and object identifiers.

Key topics and technical requirements

• Block cipher definitions and terminology - formal definitions of block, block cipher, ciphertext and key.
• Algorithm specifications - complete functional descriptions of each listed cipher (encryption/decryption steps, round functions).
• Key schedules and keying options - for example, TDEA (Triple DES) keying options and supported key lengths (128 or 192 bits as specified).
• Block lengths and supported key sizes - the standard organizes ciphers by block length (64-bit and 128-bit); AES is specified with 128/192/256-bit keys.
• Normative annexes and test vectors - includes a normative description of DES and informative test vectors to validate implementations.
• Object identifiers (OID) - assigned OIDs for each algorithm (Annex B), enabling interoperable identification in protocols.
• Implementation aids - S-box algebraic forms, feature tables and example vectors (Annexes C–E and D).

Practical applications

• Securing stored and transmitted data - use block ciphers standardized here to provide confidentiality in databases, file systems, VPNs, TLS-like protocols and encrypted messaging.
• Cryptographic library development - implementers use the formal algorithm and key-schedule descriptions and test vectors to build compliant, interoperable crypto libraries.
• Product certification and procurement - vendors and evaluators reference ISO/IEC 18033-3 when specifying acceptable block ciphers for compliance or procurement requirements.
• Interoperability in protocols - OIDs and standardized behavior enable consistent algorithm selection across systems and protocols.

Who should use this standard

• Security architects and systems designers selecting encryption primitives.
• Cryptographic engineers and library implementers validating correctness with test vectors.
• QA, compliance and procurement teams assessing supported algorithms.
• Standards bodies and protocol developers requiring normative algorithm references.

Related standards

• ISO/IEC 18033 (series): Part 1 - General; Part 2 - Asymmetric ciphers; Part 4 - Stream ciphers.
• Referenced work: ISO/IEC 9834 (object identifiers), ISO/IEC JTC 1/SC 27 (security techniques).

ISO/IEC 18033-3 is a practical, normative resource for implementing and validating block cipher algorithms used to protect data confidentiality in modern IT systems.