Abstract

In this paper, a new framework is developed for proving and adapting the recently proposed multiple-of-8 property and mixture-differential distinguishers. The above properties are formulated as immediate consequences of an equivalence relation on the input pairs, under which the difference at the output of the round function is invariant. This approach provides a further understanding of these newly developed distinguishers. For example, it clearly shows that the branch number of the linear layer does not influence the validity of the property, on the contrary of what was previously believed. We further provide an extension of the mixture-differential distinguishers and multiple-of-8 property to any SPN and to a larger class of subspaces. These adapted properties can then be exhibited in a systematic way for other ciphers than the AES. We illustrate this with the examples of Midori, Klein, LED and Skinny.

Highlights

  • The Advanced Encryption Standard (AES) is a block cipher designed by Daemen and Rijmen in 1997 and standardised by the NIST in 2001 [AES01]

  • Most of the attacks against block ciphers are based on the existence of a distinguisher, that is a non-random property that permits to distinguish within reasonable time and by using reasonable data and memory resources, a reduced-round version of the cipher instantiated with a random secret key from a random permutation

  • We describe three distinguishers based on subspace trail cryptanalysis in order to have a complete understanding of the context in which our contribution lies

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Summary

Introduction

The Advanced Encryption Standard (AES) is a block cipher designed by Daemen and Rijmen in 1997 and standardised by the NIST in 2001 [AES01]. The aim of our paper is to provide a general formulation of the mixture-differential distinguisher and of the multiple-of-8 property which can be applied in a systematic way to any cipher following the SPN construction It avoids all these redundant proofs which were previously required for each new occurrence of these properties. We show that the mixture-differential distinguishers, and by extension the multiple-of-8 property, revealed in [GRR17, Gra18] are direct consequences of the fact that the difference between two outputs of the AES round function, R(p0) + R(p1), is invariant under an equivalence relation between the plaintext pairs.

Description of the AES
Subspace trails for AES
Distinguishers based on subspace trails
A more concise and general proof
An equivalence relation between pairs of states
The multiple-of-8 property
Influence of the branch number
An alternative proof of Theorem 3
Adaptation to a general SPN construction
A more general setting for Theorem 4 and Lemma 2
A new proof of Theorem 2
Applications
The cases of Crypton and Prince
Conclusion
Full Text
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