International Association
for Cryptologic Research

In this paper, we analyze the security claims of Extended Generalized Feistel Networks (EGFNs) schemes proposed by Berger et al [1]. We provide impossible differentials for 10 rounds of EGFNs with 16 branches which add up one round to the claim of 9 rounds in the impossible differential trail. Therefore, impossible differential trail covers 10 rounds for the EGFNs scheme, which is the best result on impossible differentials of EGFNs so far. We also provide several 10 round impossible differential trails to attack EGFNs based new cipher proposals. 𝒰-method is also used by authors to assert their claim for maximum number of rounds in impossible differential trails of EGFNs. This analysis indicates that 𝒰-method does not provide optimal results for this scheme.