New Combined Attacks on Block Ciphers

Differential cryptanalysis and linear cryptanalysis are the most widely used techniques for block ciphers cryptanalysis. Several attacks combine these cryptanalytic techniques to obtain new attacks, e.g., differential-linear attacks, miss-in-the-middle attacks, and boomerang attacks. In this paper we present several new combinations: we combine differentials with bilinear approximations, higher-order differentials with linear approximations, and the boomerang attack with linear, with differential-linear, with bilinear, and with differential-bilinear attacks. We analyze these combinations and present examples of their usefulness. For example, we present a 6-round differential-bilinear approximation of s5DES with a bias of 1/8, and use it to attack 8-round s5DES using only 384 chosen plaintexts. We also enlarge a weak key class of IDEA by a factor of 512 using the higher-order differential-linear technique. We expect that these attacks will be useful against larger classes of ciphers.