Improved Single-Key Attacks on 9-Round AES-192/256

This paper focuses on key-recovery attacks on 9-round AES-192 and AES-256 under single-key model with the framework of the meet-in-the-middle attack. A new technique named key-dependent sieve is introduced to further reduce the size of lookup table of the attack, and the 9-round AES-192 is broken with 2 121 chosen plaintexts, 2(187.5) 9-round encryptions and 2(185) 128-bit words of memory. If the attack starts from the third round, the complexities would be further reduced by a factor of 16. Moreover, the whole attack is split up into a series of weak-key attacks. Then the memory complexity of the attack is saved significantly when we execute these weak attacks in streaming mode. This method is also applied to reduce the memory complexity of the attack on 9-round AES-256.