Automatic Search for a Maximum Probability Differential Characteristic in a Substitution-Permutation Network

The algorithm presented in this paper computes a maximum probability differential characteristic in a Substitution-Permutation Network (or SPN). Such characteristics can be used to prove that a cipher is practically secure against differential cryptanalysis or on the contrary to build the most effective possible attack. Running in just a few second on 64 or 128-bit SPN, our algorithm is an important tool for both cryptanalists and designers of SPN.