Improvements for Finding Impossible Differentials of Block Cipher Structures

Abstract

In this paper we improve Wu and Wang\u27s method for finding impossible differentials of block cipher structures. This improvement is more general than Wu and Wang\u27s method that it can find more impossible differentials with less time. We apply it on Gen-CAST256, Misty, Gen-Skipjack, Four-Cell, Gen-MARS, SMS4, MIBS, Camellia*, LBlock, E2 and SNAKE block ciphers. All impossible differentials discovered by the algorithm are the same as Wu\u27s method. Besides, for the 8-round MIBS block cipher, we find 4 new impossible differentials, which are not listed in Wu and Wang\u27s results. The experiment results show that the improved algorithm can not only find more impossible differentials, but also largely reduce the search time