Feistel ciphers with L2-decorrelation

Abstract

Recently, we showed how to strengthen block ciphers by decorrelation techniques. In particular, we proposed two practical block ciphers, one based on the GF(2n)-arithmetics, the other based on the x mod p mod 2n primitive with a prime p = 2n(1 + δ). In this paper we show how to achieve similar decorrelation with a prime p = 2n(1 − δ). For this we have to change the choice of the norm in the decorrelation theory and replace the L∞ norm by the L2 norm. We propose a new practical block cipher which is provably resistant against differential and linear cryptanalysis.