On Algebraic Relations of Serpent S-Boxes

Serpent is a 128-bit block cipher designed by Ross Anderson, Eli Biham and Lars Knudsen as a candidate for the Advanced Encryption Standard (AES). It was a finalist in the AES competition. The winner, Rijndael, got 86 votes at the last AES conference while Serpent got 59 votes [1]. The designers of Serpent claim that Serpent is more secure than Rijndael.In this paper we have observed that the nonlinear order of all output bits of serpent S-boxes are not 3 as it is claimed by the designers.