Improved meet-in-the-middle attacks on Crypton and mCrypton

This study presents several meet-in-the-middle attacks on reduced-round Crypton and mCrypton block ciphers. Using the generalised -set, the authors construct 5-round distinguishers on Crypton and mCrypton. Based on these distinguishers, the authors propose meet-in-the-middle attacks on 8-round Crypton and mCrypton-96/128. The attack on Crypton needs 2(121) chosen plaintexts, 2(132) encryptions and 2(130) 128-bit blocks; the attacks on mCrypton need 2(61) chosen plaintexts, 2(80) encryptions and 2(78) 64-bit blocks. Furthermore, the attack can be extended to 9 rounds for mCrypton-128 with complexities of 2(61) chosen plaintexts, 2(112) encryptions and 2(82) 64-bit blocks.