Solve Polyalphabetic Cipher Based on Intelligent System

Besides the development of technology, it has necessary to use sophisticated systems to maintain information confidentiality. One of the essential polyalphabetic encryption algorithms used to maintain information security is the Vigenere cipher, which has been developed over time to simulate the times' developments. Vigenere cipher's strength lies in the extended size of keyspace which can generate stream encrypted text. Hence the difficulty of analyzing cryptanalysis. This work focused on using a good and modern algorithm in cryptanalysis, which is the CLPSO algorithm. We applied this algorithm to enhance the fitness function used to attack the Vigenere cipher system with short and long keyspaces up to 26 characters. Through experiments, we noticed that the CLPSO algorithm successfully recognized key up to 11 characters based on only 80 characters of input ciphertext. It extracted 100% from the key when used to attack the Vigenere with keysize 25 based on 350 characters from the input and 100% from key length 26 based on 600 characters ciphertext using ciphertext only attack. Experiments have shown that the effectiveness of this algorithm is very promising in attacking Vigenere with long keys.