## Cryptology ePrint Archive: Report 2013/676

Automatic Security Evaluation and (Related-key) Differential Characteristic Search: Application to SIMON, PRESENT, LBlock, DES(L) and Other Bit-oriented Block Ciphers

Siwei Sun, Lei Hu, Peng Wang, Kexin Qiao, Xiaoshuang Ma, Ling Song

Abstract: We propose two systematic methods to describe the differential property of an S-box with linear inequalities based on logical condition modelling and computational geometry respectively. In one method, inequalities are generated according to some conditional differential properties of the S-box; in the other method, inequalities are extracted from the H-representation of the convex hull of all possible differential patterns of the S-box. For the second method, we develop a greedy algorithm for selecting a given number of inequalities from the convex hull. Using these inequalities combined with Mixed-integer Linear Programming (MILP) technique, we propose an automatic method for evaluating the security of bit-oriented block ciphers against the (related-key) differential attack, and several techniques for obtaining tighter security bounds. We successfully prove that the 24-round PRESENT-80 is secure enough to resist against standard related-key differential attacks based on differential characteristic, and the probability of the best related-key differential characteristic of the full LBlock is upper bounded by $2^{-60}$. These are the tightest security bounds with respect to the related-key differential attack published so far for PRESENT-80 and LBlock.

~~~~Moreover, we present a new tool for finding (related-key) differential characteristics automatically for bit-oriented block ciphers. Using this tool, we obtain new single-key or related-key differential characteristics for SIMON48, LBlock, DESL and PRESENT-128, which cover larger number of rounds or have larger probability than all previously known results. The methodology presented in this paper is generic, automatic and applicable to many bit-oriented block ciphers.

Category / Keywords: Automatic cryptanalysis, Related-key differential attack, Mixed-integer Linear Programming, Convex hull

Original Publication (with major differences): IACR-ASIACRYPT-2014

Date: received 22 Oct 2013, last revised 12 Sep 2014

Contact author: sunsiwei at iie ac cn

Available format(s): PDF | BibTeX Citation

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Short URL: ia.cr/2013/676

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