Cryptanalysis of Block Ciphers via Improved Simulated Annealing Technique

Cryptanalysis of ciphers has been successfully demonstrated through several techniques such as brute force attack, linear and differential cryptanalysis and heuristic optimisation methods. To demonstrate the power of heuristic optimisation techniques for attacks of modern-day ciphers, we present for the first time systematic experiments on heuristic-based attacks of modified versions of data encryption standard (DES) with 48 bits. A novel contribution of this work lies in combining the features of differential cryptanalysis and heuristic optimisation methods. This is possible by using differential cryptanalysis to obtain 42 bits of the key whereas the remaining missing 14 key bits are obtained through heuristic optimisation methods by a choice of suitable composite fitness function to capture this combined use of both these approaches. The studies reported in this paper will be useful for the attacks of other similar ciphers.