Improved results on impossible differential cryptanalysis of reduced-round Camellia-192/256

摘要

As an international standard adopted by ISO/IEC, the block cipher Camellia has been used in various cryptographic applications. In this paper, we reevaluate the security of Camellia against impossible differential cryptanalysis. Specifically, we propose several 7-round impossible differentials with the FL/FL~(-1) layer. Based on one of them, we mount impossible differential attacks on 11-round Camellia-192 and 12-round Camellia-256. The data complexities of our attacks on 11-round Camellia-192 and 12-round Camellia-256 are about 2~(120) chosen plaintexts and 2~(119.8) chosen plaintexts, respectively. The corresponding time complexities are approximately 2167-1 11 -round encryptions and 2~(220.87)12-round encryptions. As far as we know, our attacks are 2~(16.9) times and 2~(19.13) times faster than the previously best known ones but have slightly more data.