Impossible Differential Cryptanalysis of Reduced-Round Midori64 Block Cipher (Extended Version)

Impossible differential attack is a well-known mean to examine robustness of block ciphers. Using impossible differ- ential cryptanalysis, we analyze security of a family of lightweight block ciphers, named Midori, that are designed considering low energy consumption. Midori state size can be either 64 bits for Midori64 or 128 bits for Midori128; however, both versions have key size equal to 128 bits. In this paper, we mainly study security of Midori64. To this end, we use various techniques such as early-abort, memory realloca- tion, miss-in-the-middle and turning to account the inadequate key schedule algorithm of Midori64. We first show two new 7- round impossible differential characteristics which are, to the best of our knowledge, the longest impossible differential char- acteristics found for Midori64. Based on the new characteristics, we mount three impossible differential attacks for 10, 11, and 12 rounds on Midori64 with 2 87.7 , 2 90.63 , and 2 90.51 time complexity, respectively, to retrieve the master-key.