Abstract

Block ciphers are the very foundation of computer and information security. FOX, also known as IDEA NXT, is a family of block ciphers published in 2004 and is famous for its provable security to cryptanalysis. In this paper, we apply impossible differential cryptanalysis on FOX cipher. We find a 4-round impossible difference, by using which adversaries can attack 5, 6 and 7-round FOX64 with 2 71, 2 135 and 2 199 one-round encryptions respectively. Compared to the previous best attack with 2 109.4, 2 173.4 and 2 237.4 full-round encryptions to 5, 6 and 7-round FOX64, the method in this paper is the best attack to FOX cipher. This attack can also be applied to 5-round FOX128 with 2 135 one-round encryptions. Index Terms — Security, cryptography, block cipher, FOX, impossible difference

Citations