Swarm Intelligence based linear cryptanalysis of four-round Data Encryption Standard algorithm

The proliferation of computers, internet and wireless communication capabilities into the physical world has led to ubiquitous availability of computing infrastructure. With the expanding number and type of internet capable devices and the enlarged physical space of distributed and cloud computing, computer systems are evolving into complex and pervasive networks. Amidst the aforesaid rapid growth in technology, secure transmission of data is also equally important. The amount of sensitive information deposited and transmitted over the internet is absolutely critical and needs principles that enforce legal and restricted use and interpretation of data. The data needs to be protected from eavesdroppers and potential attackers who undermine the security processes and perform actions in excess of their permissions. Cryptography algorithms form a central component of the security mechanisms used to safeguard network transmissions and data storage. As the encrypted data security largely depends on the techniques applied to create, manage and distribute the keys, therefore a cryptographic algorithm might be rendered useless due to poor management of the keys. This paper presents a novel computational intelligence based approach for known ciphertext-only cryptanalysis of four-round Data Encryption Standard algorithm. In ciphertext-only attack, the encryption algorithm used and the ciphertext to be decoded are known to cryptanalyst and is termed as the most difficult attack encountered in cryptanalysis. The proposed approach uses Swarm Intelligences to deduce optimum keys according to their fitness values and identifies the best keys through a statistical probability based fitness function. The results suggest that the proposed approach is intelligent in finding missing key bits of the Data Encryption Standard algorithm.