Paper 2008/151

Impossible Differential Cryptanalysis of CLEFIA

Bing Sun, Ruilin Li, Mian Wang, Ping Li, and Chao Li

Abstract

This paper mainly discussed the impossible differerential crypt- analysis on CLEFIA which was proposed in FSE2007. New 9-round impossible differentials which are difrererent from the previous ones are discovered. Then these differerences are applied to the attack of reduced-CLEFIA. For 128-bit case, it is possible to apply an impossible differen-tial attack to 12-round CLEFIA which requires 2^110.93 chosen plaintexts and the time complexity is 2^111. For 192/256-bit cases, it is possible to apply impossible differential attack to 13-round CLEFIA and the chosen plaintexts and time complexity are 2^111.72 and 2^158 respectively. For 256-bit cases, it needs 2^112.3 chosen plaintexts and no more than 2^199 encryptions to attack 14-round CLEFIA and 2^113 chosen plaintexts to attack 15-round 256-bit CLEFIA with the time complexity less than 2^248 encryptions.