Impossible differential cryptanalysis of MARS-like structures

The MARS-like structure is a generalised Feistel structure. Unified impossible differential (UID) method is an effective method to discover impossible differential characteristics for block cipher structures. In this study, for a specific kind of MARS-like structure, the authors use UID to show that when n, the number of subblocks, is even, there always exist 3n - 1 rounds impossible differentials. Moreover, the authors prove that when n is odd, the MARS-like structure has impossible differentials for any number of rounds, which is a clear but interesting result.