Cryptology ePrint Archive: Report 2016/790

Conditional Cube Attack on Reduced-Round Keccak Sponge Function

Senyang Huang, Xiaoyun Wang, Guangwu Xu, Meiqin Wang, Jingyuan Zhao

Abstract: The security analysis of Keccak, the winner of SHA-3, has attracted considerable interest. Recently, some attention has been paid to the analysis of keyed modes of Keccak sponge function. As a notable example, the most ecient key recovery attacks on Keccak-MAC and Keyak were reported at EUROCRYPT'15 where cube attacks and cubeattack- like cryptanalysis have been applied. In this paper, we develop a new type of cube distinguisher, the conditional cube tester, for Keccak sponge function. By imposing some bit conditions for certain cube variables, we are able to construct cube testers with smaller dimensions. Our conditional cube testers are used to analyse Keccak in keyed modes. For reduced-round Keccak-MAC and Keyak, our attacks greatly improve the best known attacks in key recovery in terms of the number of rounds or the complexity. Moreover, our new model can also be applied to keyless setting to distinguish Keccak sponge function from random permutation.We provide a searching algorithm to produce the most ecient conditional cube tester by modeling it as an MILP (mixed integer linear programming) problem. As a result, we improve the previous distinguishing attacks on Keccak sponge function signi cantly. Most of our attacks have been implemented and veri ed by desktop computers. Finally we remark that our attacks on the the reduced-round Keccak will not threat the security margin of Keccak sponge function.

Category / Keywords: Keccak-MAC, Keyak, cube tester, conditional cube variable, ordinary cube variable

Original Publication (with minor differences): IACR-EUROCRYPT-2017

Date: received 18 Aug 2016, last revised 25 Jan 2017

Contact author: xiaoyunwang at mail tsinghua edu cn

Available format(s): PDF | BibTeX Citation

Version: 20170126:045225 (All versions of this report)

Short URL: ia.cr/2016/790

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