Differential-Linear Cryptanalysis of Serpent

Serpent is a 128-bit SP-Network block cipher consisting of 32 rounds with variable key length (up to 256 bits long). It was selected as one of the 5 AES finalists. The best known attack so far is a linear attack on an 11-round reduced variant. In this paper we apply the enhanced differential-linear cryptanalysis to Serpent. The resulting attack is the best known attack on 11-round Serpent. It requires 2125.3 chosen plaintexts and has time complexity of 2139.2. We also present the first known attack on 10-round 128-bit key Serpent. These attacks demonstrate the strength of the enhanced differential-linear cryptanalysis technique.