1 Self evaluation of FEAL - NX

1 Evaluation of security 1.1. Differential cryptanalysis In extending differential cryptanalysis, Aoki , Kobayashi, and Moriai [1] greatly reduced the computational amount needed [2]. They determined that differential cryptanalysis could not be applied to FEAL with more than 32 rounds. Biham et al. [3] proposed a new cyptanalysis of Skipjack [4] using impossible differentials. Although regular differential cryptanalysis utilizes high-probability differential characteristic, the cryptanalysis using impossible differentials utilizes low or zero-probability differential characteristic. Aoki developed a new cryptanalysis approach based on impossible differentials and applied it to FEAL. He showed that the upper limit of FEAL, against impossible differentials, was 9 rounds [5] .