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Chaos-based image encryption has great significance as a branch of image security. So, a series of chaos-based cryptosystems protecting digital images are proposed in recent years. But, most of them have been broken as a result of poor encryption structure. This research paper suggests an effective image encryption structure to resist possible attacks. The proposed method employs plain image related Henon map (PIHM) for shuffling and diffusion processes in a connected way which is different from conventional chaotic based image encryption systems, since the initial conditions of diffusion process are established based on the initial conditions of shuffling process. The principle of confusion is achieved by shuffling the pixels over all the rows and columns. And the diffusion is ensured by using XOR operation of current shuffled pixel value with the previous value, and random pixel produced from PIHM map. The results of simulation and security analysis indicate that the proposed scheme has desirable encryption effects and is robust against different common attacks.

Particle swarm optimization (PSO) based cryptanalysis has acquired much attention because it has a fast convergence rate. This paper investigates the use of a new approach which is PSO depending on the clustering algorithm (CLPSO) to break the transposition cipher system in appropriate time. The dynamic of CLPSO is different from existing PSO in population size, topology and the ways to find the best solution. CLPSO start’s with using high population size (particles) and then applying preprocessing operation in order to reduce this population and then partition this population into several clusters based on using semi CLARANS algorithm and allow particles to share information in different clusters and give the particles ability to move from one cluster to another depending on the values of fitness function. Experimental results of the proposed CLPSO were very promising and the results proved that the CLPSO algorithm reduces the number of tries that needed to attack long key transposition cipher in almost real time using ciphertext-only attack. This new method allows recovering key length up to 35 with no more than 58.3 second as maximum consuming time. In this case study, different parameters such as: population sizes (100-5000), key size (10 - 35) and length of ciphertext (250 - 5000) were used.