USEs OF GA, PSO and MPSO TO BREAK TRANSPOSITION CIPHER SYSTEM: comparative study

Abstract

GA is an adjustable search method that has the ability for search in smart way to find the best solution and trying to reduce the time that required for obtaining the optimal solution. Particle Swarm Optimization (PSO) algorithm emulate the behavior of a swarm of fish and bird flocks. It's a heuristic global optimization method which can be implemented and applying to solve various optimization problems. The most attractive of using PSO is that it has a fast convergence than the other global optimization methods. Modify PSO (MPSO) is a relatively new approach to attacks transposition cipher which it depends on using multi swarms rather than single swarm and allowing the particles in all swarms to exchange information between them in order to obtains the best solution from all swarms. This research focuses on use GA, PSO and MPSO to cryptanalyze transposition cipher based on a new tools to determine the fitness function by calculating the Diagram(DG), Trigram(TG) and Quadgram (QG) frequency of letters. It is shown that such algorithms can be used to reduce the number of trails which are needed to determined the initial states of the attacked systems using ciphertext only attack. Experimental results show the successful applications of GA, PSO and MPSO in cryptanalysis of transposition cipher system. Also, the experimental results indicate that the MPSO is more powerful than the other techniques in cryptanalysis transposition depending on the accuracy of results.