Differential Cryptanalysis and Impossible Differential Characteristics of Extended Feistel Networks

Abstract. Impossible differential cryptanalysis (IDC) is a variant of differential cryptanalysis (DC) against block ciphers whereby impossi-ble differential characteristics are used to retrive 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 [1]. In this paper, we will first examine the security of Ex-tended Feistel Networks (EFN) against DC and then use the U-method introduced in [1] to find impossible differential characteristics of EFN