Cryptanalysis of Reduced-Round Midori64 Block Cipher

Midori is a hardware-oriented lightweight block cipher designed by Banik et al. in ASIACRYPT 2015. It has two versions according to the state sizes, i.e. Midori64 and Midori128. In this paper, we explore the security of Midori64 against truncated differential and related-key differential attacks. By studying the compact representation of Midori64, we get the branching distribution properties of almost MDS matrix used by Midori64. By applying an automatic truncated differential search algorithm developed by Moriai et al. in SAC 1999, we get 3137 4-round truncated differentials of Midori64. In addition, we find some 2-round iterative differential patterns for Midori64. By searching the differential characteristics matching the differential pattern, we find some iterative 2-round differentials with probability of 2−24, based on these differentials, a 11-round related-key differential characteristic is constructed. Then we mount a 14-round(out of 16 full rounds) related-key differential attack on Midori64. As far as we know, this is the first related-key differential attack on Midori64.