[Resource Topic] 2019/126: New Automatic search method for Truncated-differential characteristics: Application to Midori, SKINNY and CRAFT

Welcome to the resource topic for 2019/126

Title:
New Automatic search method for Truncated-differential characteristics: Application to Midori, SKINNY and CRAFT

Authors: AmirHossein E. Moghaddam, Zahra Ahmadian

Abstract:

In this paper, using Mixed Integer Linear Programming, a new automatic search tool for truncated differential characteristic is presented. Our method models the problem of finding a maximal probability truncated differential characteristic, which is able to distinguish the cipher from a pseudo random permutation. Using this method, we analyse Midori64, SKINNY64/X and CRAFT block ciphers, for all of which the existing results are improved. In all cases, the truncated differential characteristic is much more efficient than the (upper bound of) bit-wise differential characteristic proven by the designers, for any number of rounds. More specifically, the highest possible rounds, for which an efficient differential characteristic can exist for Midori64, SKINNY64/X and CRAFT are 6, 7 and 10 rounds respectively, for which differential characteristics with maximum probabilities of 2^{-60}, 2^{-52} and 2^{-62.61} (may) exist. Using our new method, we introduce new truncated differential characteristics for these ciphers with respective probabilities 2^{-54}, 2^{-4} and 2^{-24} at the same number of rounds. Moreover, the longest truncated differential characteristics found for SKINNY64/X and CRAFT have 10 and 12 rounds, respectively. This method can be used as a new tool for differential analysis of SPN block ciphers.

ePrint: https://eprint.iacr.org/2019/126

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