Strength of Round function in RC6 Block Cipher against Higher Order Differential Attack

概要

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RC6 is a new block cipher; a candidate of AES, proposed by Rivest et al in 1998. AES version of RC6 has 20 rounds and 32[bit] word length. In this paper, we estimate strength of Round function in RC6 against Higher Order Differential Attack. Since RC6 uses Sub-keys by integer addition, we show that it has weak keys which enable attacks using lower order differentials. We estimate its strength by calculating the ratio of weak keys. If weak keys are used, attacks are feasible, so the ratio of weak keys equals to the probability of successful attack. As the results, we found that 5 round Round function is attackable using 16th order differential with about 1.5×10^<-4>% of successful attack. And 6 round Round function is attackable using 32nd order differential with higher probability than 2^<-32>. This attack needs 2^<32> chosen plain texts and 2^<64> computational cost.
社団法人電子情報通信学会の論文
2000-01-25