Cryptology ePrint Archive: Report 2014/736

Cube Attacks and Cube-attack-like Cryptanalysis on the Round-reduced Keccak Sponge Function

Itai Dinur and Pawel Morawiecki and Josef Pieprzyk and Marian Srebrny and Michal Straus

Abstract: In this paper, we comprehensively study the resistance of keyed variants of SHA-3 (Keccak) against algebraic attacks. This analysis covers a wide range of key recovery, MAC forgery and other types of attacks, breaking up to 9 rounds (out of the full 24) of the Keccak internal permutation much faster than exhaustive search. Moreover, some of our attacks on the 6-round Keccak are completely practical and were verified on a desktop PC. Our methods combine cube attacks (an algebraic key recovery attack) and related algebraic techniques with structural analysis of the Keccak permutation. These techniques should be useful in future cryptanalysis of Keccak and similar designs.

Although our attacks break more rounds than previously published techniques, the security margin of Keccak remains large. For Keyak -- a Keccak-based authenticated encryption scheme -- the nominal number of rounds is 12 and therefore its security margin is smaller (although still sufficient).

Category / Keywords: secret-key cryptography / Keccak, SHA-3, sponge function, cube attack

Date: received 19 Sep 2014, last revised 20 Sep 2014

Contact author: pawel morawiecki at gmail com

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Version: 20140920:080434 (All versions of this report)

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