International Association
for Cryptologic Research

In this paper, we show that it is inaccurate to apply the hypothesis of independent round keys to search for differential characteristics of a block cipher with a simple key schedule. Therefore, the derived differential characteristics may be valid. We develop a SAT-based algorithm to verify the validity of differential characteristics. Furthermore, we take the key schedule into account and thus put forward an algorithm to directly find the valid differential characteristics. All experiments are performed on Midori64 and we find some interesting results.