[Resource Topic] 2024/802: On Maximum Size Simultaneous Linear Approximations in Ascon and Keccak and Related Translation and Differential Properties

Welcome to the resource topic for 2024/802

Title:
On Maximum Size Simultaneous Linear Approximations in Ascon and Keccak and Related Translation and Differential Properties

Authors: Nicolas T. Courtois, Frédéric Amiel, Alexandre Bonnard de Fonvillars

Abstract:

In this paper we study the S-box known as Xi initially proposed by Daemen in 1995 and very widely used ever since in Keccak, Ascon, and many other. This type of ciphers is typically analyzed [in recent research] in terms of subspace trail attacks [TeDi19] and vector space invariants. An interesting question is then, when different spaces are mapped to each other by translations with a constant.
In this paper we relax this fundamental question and we consider arbitrary sets of points and their translations. We generalize previous S-box partial linearization results on Keccak and Ascon from Eurocrypt 2017. We basically introduce new ways to linearize the Ascon S-box to the maximum possible extent. On this basis we show further remarkable properties and some surprising connections between [simultaneous] linear and [prominent] differential properties. We exhibit a new family of maximum size and optimal approximation properties with 11 points, beyond the maximum size of any set in the DDT table.
We prove a theorem which guarantees that this type of properties are stable by arbitrary input-side translations which holds for all quadratic permutations. All this will be placed in the context of previous work on classification of 5-bit quadratic permutations.

ePrint: https://eprint.iacr.org/2024/802

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