Abstract: ARIA cipher is a standard block cipher published by South Korean. Its block size is 128 bits and supports three key lengths: 128 bits, 192 bits, and 256 bits. In this paper, the security of a variant ARIA cipher using the same S boxes against the meet-in-the-middle attack is examined. Based on the structure of
the cipher, we design 4-round, 5-round, and 6-round distinguishers, respectively. Moreover, some new attacks on 7-round ARIA-192, 8-round ARIA-192, and 9-round ARIA-256 are proposed. It is shown that the security of ARIA will be reduced significantly if the cipher only uses a nonlinear S box. Furthermore, if the linear and nonlinear layers are not properly combined, one can break the equivalent tradeoff between the dada complexity and the preprocess time complexity under a dada-time-memory tradeoff attack. In this case, a more effective attack may be obtained.

Key words: block cipher, ARIA cipher, meet-in-the-middle attack, time complexity