Abstract: mCrypton is a lightweight block cipher introduced in Information Security Application 2006 by Lim and Korkishko. mCrypton-64/96/128 denote 3 versions of the cipher with 64/96/128 b keys respectively. In this paper, we apply the meet-in-the-middle (MITM) attack on 8-round mCrypton-96, which improves the best MITM attack result on mCrypton-96 by 1 round.When analyzing the security of block ciphers, using key relations to reduce the time complexity, memory complexity and data complexity is a common method. From the property of the key schedule of mCrypton-96, we know that each round key could calculate some information of the internal register by the algebraic structure of the key schedule, and some round keys could be deduced from the other round keys. By using the relationship of key schedule and the properties of S-box, we present a MITM attack on 8-round mCrypton-96 based on the 4-round distinguisher by adding 1 round on the top and 3 rounds at the bottom. The time, memory and data complexities of the attack are 2\+{93.5} encryptions, 2\+{47} B and 2\+{57} chosen plaintexts respectively. It is illustrated that mCrypton-96 not only has an efficient performance but also possesses strong security.

Key words: cryptanalysis, meet-in-the-middle (MITM) attack, block ciphers, mCrypton, relationship of keys