Impossible Differential Cryptanalysis for block cipher structures

Impossible Differential Cryptanalysis(IDC) [4] uses impossible differential characteristics to retrieve a subkey material for the first or the last several rounds of block ciphers. Thus, the security of a block cipher against IDC can be evaluated by impossible differential characteristics. In this paper, we study impossible differential characteristics of block cipher structures whose round functions axe bijective. We introduce a widely applicable method to find various in possible differential characteristics of block cipher structures. Using this method, we find various impossible differential characteristics of known block cipher structures: Nyberg's generalized Feistel network, a generalized CAST256-like structure (14], a generalized MARS-like structure [14], a generalized RC6-like structure [14), and Rijndael structure.