摘要：Problem statement: With the demand for effective network security is increasing, it becomes necessary to find the strength and weaknesses of the existing cryptographic methods. Vigenere cipher, a classical cipher is analyzed for its strength against a cipher only attack. Approach: The cipher texts so selected were of various sizes up to 1 Kb. A biologically inspired algorithm, Particle Swarm Optimization (PSO) was applied to the problem of crypt analyzing the Vigenere cipher. PSO was an optimization technique and its used on the problem of optimizing the fitness function designed for Vigenere cipher was performed. Results: It was seen that PSO is able to find the keyword employed and the other possible combinations for the keyword. Conclusion: PSO is better than genetic algorithm to solve Vigenere cipher and can be used to find the keyword with lesser size.
