Cryptology ePrint Archive: Report 2019/622

Extended Truncated-differential Distinguishers on Round-reduced AES

Zhenzhen Bao and Jian Guo and Eik List

Abstract: Distinguishers on round-reduced AES have attracted considerable attention in the recent years. While the number of rounds covered in key-recovery attacks did not increase, subspace, yoyo, mixture-differential, and multiple-of-n cryptanalysis advanced the understanding of the properties of the cipher. For substitution-permutation networks, integral attacks are a suitable target for extension since they usually end after a linear layer sums several subcomponents. Based on results by Patarin, Chen et al. already observed that the expected number of collisions for a sum of permutations differs slightly from that for a random primitive. Though, their target remained lightweight primitives. The present work illustrates how the well-known integral distinguisher on three-round AES resembles a sum of PRPs and can be extended to truncated-differential distinguishers over 4 and 5 rounds. In contrast to previous distinguishers by Grassi et al., our approach allows to prepend a round that starts from a diagonal subspace. We demonstrate how the prepended round can be used for key recovery with a new differential key-recovery attack on six-round AES. Moreover, we show how the prepended round can also be integrated to form a six-round distinguisher. For all distinguishers and the key-recovery attack, our results are supported by implementations with Cid et al.'s established Small-AES version. While the distinguishers do not threaten the security of the AES, they try to shed more light on its properties.

Category / Keywords: secret-key cryptography / cryptanalysis, block cipher, AES

Date: received 1 Jun 2019, last revised 4 Oct 2020

Contact author: eik list at uni-weimar de,zzbao@ntu edu sg,guojian@ntu edu sg

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Version: 20201004:091707 (All versions of this report)

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