Related key differential attacks on 27 rounds of XTEA and full-round GOST

In this paper, we present a related key truncated differential attack on 27 rounds of XTEA which is the best known attack so far. With an expected success rate of 96.9%, we can attack 27 rounds of XTEA using 2^20.5 chosen plaintexts and with a complexity of 2^115.15 27-round XTEA encryptions. We also propose several attacks on GOST. First, we present a distinguishing attack on full-round GOST, which can distinguish it from a random permutation with probability 1-2^-64 using a related key differential characteristic. We also show that H. Seki et al.'s idea combined with our related key differential characteristic can be applied to attack 31 rounds of GOST . Lastly, we propose a related key differential attack on full-round GOST. In this attack, we can recover 12 bits of the master key with 2³⁵ chosen plaintexts, 2³⁶ encryption operations and an expected success rate of 91.7%.