A Note on the Higher Order Differential Attack of Block Ciphers with Two-Block Structures

摘要

We study on the security against higher order differential attack on block ciphers with two-block structure which have provable security against differential and linear cryptanalysis. The two-block structures are classified three types according to the location of round function such as C(Center)-type, R(Right)-type, and L(Left)-type. We prove that in the case of 4 rounds encryption function, these three types provide an equal strength against higher order differential attack and that in the case of 5 or more rounds, R-type is weaker than C-type and L-type. Moreover, we show that these facts also hold similarly for probabilistic higher order differential attack.