Improved “Partial Sums”-based Square Attack on AES
Michael Tunstall · 2012
The Square attack as a means of attacking reduced round variants of AES was described in the initial description of the Rijndael block cipher.This attack can be applied to AES, with a relatively small number of chosen plaintext-ciphertext pairs, reduced to less than six rounds in the case of AES-128 and seven rounds otherwise and several extensions to this attack have been described in the literature.In this paper we describe new variants of these attacks that have a smaller time complexity than those present in the literature.Specifically, we demonstrate that the quantity of chosen plaintext-ciphertext pairs can be halved producing the same reduction in the time complexity.We also demonstrate that the time complexity can be halved again for attacks applied to AES-128 and reduced by a smaller factor for attacks applied to AES-192.This is achieved by eliminating hypotheses on-the-fly when bytes in consecutive subkeys are related because of the key schedule.