On the pseudorandomness of the AES Finalists - RC6 and serpent

Abstract

Luby and Rackoff idealized DES by replacing each round function with one large random function. In this paper, we introduce a primitive-wise idealization in which some of the primitive operations of the round function are left untouched and some of them are replaced with small random functions or permutations. We then prove that a four round primitive-wise idealized RC6 is not a pseudorandom per-mutation and a three round primitive-wise idealized Serpent is a super- pseudorandom permutation.