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Symmetric Cryptography Research


Structure of PC-MAC-AES

Realizing the speed and security

A Message Authentication Code, MAC, is a secret-key function to assure the message authenticity.

PC-MAC-AES is a MAC function based on AES. A unique feature of PC-MAC-AES is that it achieves a faster operation than AES itself. There are some standard block cipher-based MACs, such as CBC-MAC or CMAC. While these MACs have provable security based on AES's security, they use AES as a black-box and need at least one AES operation per one message block. As AES consists of 10 iterations of a keyed permutation called round function, this implies that standard AES-based MACs require 10 AES rounds for each message block.

Unlike these MACs, PC-MAC-AES combines 4-round AES and 10-round AES (i.e. normal AES) and allows to process each message block using 4 to 7 rounds. This means that PC-MAC-AES is 1.4 to 2.5 times faster than standard AES-based MACs. Furthermore, thanks to the AES round function's characteristic (which is not a computational assumption) PC-MAC-AES is provably secure based on (10-round) AES's security, i.e., the same security as (e.g.) CBC-MAC-AES.

PC-MAC-AES was proposed at FSE 2006, a conference held by International Association for Cryptologic Research (IACR). The approach of PC-MAC-AES, that is, combining a block cipher and its component to build a scheme with provable security, may gradually gain a popularity.

Kazuhiko Minematsu, Yukiyasu Tsunoo. "Provably Secure MACs from Differentially-Uniform Permutations and AES-Based Implementations" (pdf , slide),

Matthew J. B. Robshaw (Ed.): Fast Software Encryption, 13th International Workshop, FSE 2006, Graz, Austria, March 15-17, 2006, Revised Selected Papers. Lecture Notes in Computer Science 4047 Springer 2006, pp. 226-241.


PC-MAC-AES is in evaluation of CRYPTREC, a crypto standardization effort for Japanese e-government.

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