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A Strategy for Constructing Fast Round Functions with Practical Security Against Differential and Linear Cryptanalysis
Description
In this paper, we study a strategy for constructing fast and practically secure round functions that yield sufficiently small values of the maximum Differential and linear probabilities p, q. We consider mn- bit round functions with 2-round SPN structure for Feistel ciphers. In this strategy, we regard a linear transformation layer as an n × n matrix P over {0,1}. We describe the relationship between the matrix representation and the actual construction of the linear transformation layer. We propose a search algorithm for constructing the optimal linear transformation layer by using the matrix representation in order to minimize probabilities p, q as much possible. Furthermore, by this algorithm, we determine the optimal linear transformation layer that provides p ≤ ps5, q ≤ qs5 in the case of n = 8, where ps, qs denote the maximum differential and linear probabilities of s-box.