Cryptanalysis of Transposition Ciphers with Long Key Lengths Using an Improved Genetic Algorithm

In Today's world, with increasing usage of computer networks and internet, the importance of network, computer and information security is obvious. One of the widely used approaches for information security is Cryptography. Cryptanalysis is a way to break cryptography without having the encryption key. This paper presents an approach to the cryptanalysis of transposition ciphers using an improved GA with a novel fitness function. The fitness function is evaluated based on the most common bigrams and trigrams. Dynamic population size is proposed and also the crossover and mutation operators are taken randomly. Results show that the proposed algorithm is effective for cryptanalysis of transposition cipher with long key lengths up to 25 due to its strong reliability. The algorithm has also high convergence speed and minimum error.