Breaking a Playfair Cipher Using Memetic Algorithm

Abstract

The Playfair cipher operates on pairs of letters. The ciphertext is broken into groups of blocks, each block contains two letters. Encryption and decryption cipher depends on key search, which is a square matrix that contains 5x5 letters. The matrix contains every letter except the letter j.In this paper, the cryptanalyst of a Playfair is presented using search techniques. It is a Memetic Algorithm, another method is used to know a key through correct Digram letters, which is used as an essential factor in the cryptanalyst ciphertext. Results without memetic algorithm and with it have been compared, to see which one has the best solution. The result clears that the memetic algorithm has the best solution more than a classical method, and is faster than without using it, which has an optimal solution. The length of the text is 1802 letters. The key size is 25 letters as a matrix 5x5. All the algorithms were programmed using Matlab programming as M-file and tested successfully.