Diffusion and Security Evaluation of Feistel-PG

Feistel-PG structure is a new specific Gen-eralized Feistel structure (GFS) adopted in DBlock and LHash. Its main feature is adding a sbox-size permutation before the round function. Different choices of the per-mutation may aff ect the security property of ciphers with Feistel-PG structure but how it eff ects is not clear. We evaluate the values of diffusion round for all possible pa-rameters and summarize the characteristics of optimum shuffles. The results show that one special kind of Feistel-PG achieves full diffusion in less cost than the improved GFS. This advantage may attract the designers' interests and this kind of Feistel-PG ciphers are suggested to de-signers. We also evaluate the security of suggested ciphers against various byte-oriented attacks, including differential cryptanalysis, linear cryptanalysis, impossible differential attack and integral attack. Some permutations with opti-mum diffusion but relatively weaker security are filtered out and these permutations should be avoided by design-ers.