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 2 35 chosen plaintexts, 2 36 encryption operations and an expected success rate of 91.7%.

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