A Novel Chosen Plaintext Attack Against  Aes Using Key Partitioning Principle

Amr M. Ashry; Alaa El–Din R. Shehata; Ashraf D. El–Bayoumy

Volume : II, Issue : X, October - 2013

A Novel Chosen Plaintext Attack Against Aes Using Key Partitioning Principle

Amr M. Ashry, Alaa El Din R. Shehata, Ashraf D. El Bayoumy

Abstract :

The majority of the published attacks on reduced–round variants of block ciphers seeks to maximize the number of rounds to be oken, using less data than the entire codebook and less time than exhaustive key search. In this paper, a novel key partitioning chosen plaintext attack against reduced–rounds AES variants up to 4 rounds that uses only 33 chosen plaintext–ciphertext pairs, a workload of 247 (for three round variant) and 217 bytes of memory is introduced. The attack depends upon the internal structure of the AES round function, the differential characteristics of the AES S–BOX and the key partitioning in which each key byte will be processed individually independent to the other key bytes. To clarify the idea of the attack a round by round cryptanalysis till the fourth round of the AES will be followed. The results will show that a bit–level permutation is more efficient than byte–level permutation used in the AES round function. Hence, the use of a bit–level permutation in the AES round function instead of a byte level permutation is an achievement of this work as a counter measure for such type of attack.