Impossible Differentials of SPN Ciphers

摘要

An upper bound of the length of impossible differentials for an SPN structure was presented at EUROCRYPT 2016. This paper mainly focuses on the lengths of impossible differentials for two specific SPN structures. The details of the S-boxes could be exploited to construct longer impossible differentials for ciphers adopting these structures. For Kuznyechik and the internal permutation of PHOTON, we can construct 3-round and 5-round impossible differentials, respectively. The lengths of impossible differentials of these two ciphers are 1 more round compared with the lengths of impossible differentials of the structures deduced from the corresponding ciphers.