Differential Fault Analysis of Twofish

摘要

In this paper we propose Differential Fault Analysis (DFA) of Twofish which was one of the five AES finalists. It uses the concept of key-dependent S-boxes and Pseudo-Hadamard Transform, which make the cipher secure against differential attack. Each S-box is dependent on key because of which the S-box is not known to the attacker. Therefore, the existing DFA techniques which use the differential properties of S-box are not directly applicable to Twofish. We propose DFA based on an approximation technique. The attack retrieves the secret key using around 320 pairs of fault-free and faulty ciphertexts with attack time complexity of 2~(40). To the best of author's knowledge this is the first time a DFA attack is proposed on a cipher like Twofish which uses key-dependent S-box.