Overview
ISO/IEC 18033-7:2022 specifies tweakable block ciphers - symmetric permutations parameterized by a secret key and a public tweak. These primitives are defined as generic building blocks for cryptographic schemes such as encryption, Message Authentication Codes (MACs) and authenticated encryption. The standard defines five concrete algorithms: Deoxys-TBC-256, Deoxys-TBC-384, Skinny-64/192, Skinny-128/256 and Skinny-128/384 and provides algorithmic details, usage requirements, numerical examples and object identifiers for implementation.
Key topics and technical requirements
- Definitions and notation: terms such as block, tweak, tweakey (concatenation of key and tweak), symbols and bit operations are formalized.
- Algorithm specifications: full descriptions of two Deoxys-TBC versions and three Skinny versions, including data layout, round counts (Deoxys-TBC-256: 14 rounds; Deoxys-TBC-384: 16 rounds), encryption and decryption pseudocode, and tweakey schedules.
- Round structure (Deoxys-TBC): AES-like round composition with AddSubTweakey, SubBytes (AES S-box provided), ShiftRows, and MixBytes (AES MDS matrix defined). Inverse operations for decryption are specified (SubBytesInv, ShiftRowsInv, MixBytesInv).
- Tweakey usage rules: the standard permits flexible allocation of tweakey bits between key and tweak, but requires the key size to be at least 128 bits and mandates that keying material not be reused across instances with differing tweak sizes.
- Usage limits and recommendations: the document includes constraints on particular versions (see Clause 5) and notes on modes of operation that require stricter repeatability conditions for tweaks.
- Supporting material: Annex A contains numerical examples; Annex B defines object identifiers (OIDs) for algorithm identification.
Practical applications and who should use it
- Cryptographic implementers: libraries, hardware accelerators and firmware developers implementing block cipher primitives will use this standard to ensure interoperable tweakable block cipher behavior.
- Protocol and security architects: designers of authenticated encryption, nonce misuse-resistant modes, MACs and other cryptographic protocols can use the specified primitives as building blocks.
- Standards bodies and evaluators: assessors and integrators who need standardized algorithm identifiers (OIDs) and test vectors.
- Product vendors: companies producing secure chips, IoT devices, or constrained systems that require vetted cipher primitives.
Keywords naturally integrated: ISO/IEC 18033-7:2022, tweakable block cipher, Deoxys-TBC, Skinny, tweakey, encryption algorithms, authenticated encryption, Message Authentication Codes, block cipher standard.
Related standards
- Part of the ISO/IEC 18033 series (encryption algorithms). Consult ISO and IEC catalogues for other parts and for interoperability guidance.
