Séminaire

Date : 9 octobre 2025 15:00 - Salle :A102 Computing the differential probability of trails in permutations Prof. Joan DAEMAN - Radboud University - the Netherlands

In differential cryptanalysis, that exploits predictable propagation of differences, differential trails play a central role. Such a trail is a sequence of patterns $(a_0,a_1,a_2, \ldots)$ specifying the propagation of an input difference through an iterated block cipher or permutation. Its differential probability (DP) is the probability that a pair of inputs $(x,x+a_0)$ with random $x$ exhibits the sequence of differences $a_1, a_2, \ldots$ through the rounds. Usually the DP is approximated by the product of the DP of the round differentials $(a_{i-1},a_{i})$. Research has shown that for permutations, and block ciphers with fixed key, this approximation can be very inaccurate, even for mainstream ciphers such as AES. A framework for the correct computation was proposed by Tim Beyne and Vincent Rijmen in the form of they call quasidifferential trails. In this presentation we will present a different approach to the problem and make the link with earlier work.

https://fr.wikipedia.org/wiki/Joan_Daemen