Revisiting impossible differentials of MARS‐like structures
Lei Cheng, Chao Li · IET Information Security · 2017
The MARS‐like structure is a generalised Feistel structure. In 2015, Xue and Lai proved that there always exist (3 n − 1)‐round impossible differentials of MARS‐like structures with n subblocks, as long as the round function is bijective. In this study, the length of the impossible differentials is extended by 1 round supposing that the MARS‐like structure adopts the bijective round function of SP‐type, i.e. the round function is decomposed into a substitution layer followed by a linear diffusion layer. It is surprised that such result is irrelevant to both the specifics of the S‐boxes in the substitution layer and the specifics of the linear transformations in the diffusion layer.