Feistel Ciphers with L 2-Decorrelation

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.