Efficiency analysis of gradient statistical attack on block ciphers RC6, MARS, CAST-128, IDEA, Blowfish
This paper is devoted to the pilot study of statistical techniques in cryptanalysis on the basis of block ciphers RC6, MARS, CAST-128, IDEA and Blowfish. The suggested gradient attack is based on statistical test attack called the «book stack». The described scheme and modifed attacks can significantly reduce the complexity of finding the secret key in comparison with previously known types of attacks. This paper studies the effectiveness of gradient statistical attack demonstrating its modern practical and theoretical application (9 rounds of RC6, 21 rounds of MARS and 4 rounds of CAST-128). Analytical dependence between effectively attacked rounds and time/hardware complexity is derived. In addition, in the case of RC6 and MARS, modifications significantly reducing space and operational complexity were developed. Also, this paper shows a selection method of optimum parameters of attack; operational and space complexity were investigated and their dependence on parameters and ciphertext size were shown. Theoretical demand for computing power needed to carry out the attack is described.