Ant-Crypto, a Cryptographer for Data Encryption Standard Salabat Khan, Armughan Ali and Mehr Yahya Durrani Dept. of Computer Science, COMSATS Institute of Information Technology, Attock Campus, Pakistan Abstract Swarm Intelligence and Evolutionary Techniques are attracting the cryptanalysts in the field of cryptography. This paper presents a novel swarm based attack called Ant-Crypto (Ant- Cryptographer) for the cryptanalysis of Data Encryption Standard (DES). Ant-Crypto is based on Binary Ant Colony Optimization (BACO) i.e. a binary search space based directed graph is modeled for efficiently searching the optimum result (an original encryption key, in our case). The reason that why evolutionary techniques are becoming attractive is because of the inapplicability of traditional techniques and brute force attacks against feistel ciphers due to their inherent structure based on high nonlinearity and low autocorrelation. Ant-Crypto uses a known-plaintext attack to recover the secret key of DES which is required to break/ decipher the secret messages. Ant-Crypto iteratively searches for the secret key while generating several candidate optimum keys that are guessed across different runs on the basis of routes completed by ants. These optimum keys are then used to find each individual bit of the 56 bit secret key used during encryption by DES. Ant-Crypto is compared with some other state of the art evolutionary based attacks i.e. Genetic Algorithm and Comprehensive Binary Particle Swarm Optimization. The experimental results show that Ant-Crypto is an effective evolutionary attack against DES and can deduce large number of valuable bits as compared to other evolutionary algorithms; both in terms of time and space complexity. Keywords: Ant-Crypto, Binary Ant Colony Optimization, Comparison of Optimization Techniques, Cryptanalysis of Data Encryption Standard. 1. Introduction Most important and precious element in any Information/ Communication system is DATA. Apart from giving us information and knowledge about past events/ activities and patterns, analysis of data can also help us in decision making process, keeping in view the objectives to be achieved in future. There are numerous techniques to store, retrieve and mine the data in databases and data warehouses but in this competitive world where adversaries can illegally access the data, the only way to survive and compete the adversaries is to keep the valuable data, safe and secure. The data cannot be kept secure using classical security techniques e.g. locks; either physically or electronically. In the literature, two inevitable categories of attacks are described; one is passive attack and the other is active attack. In the passive attack, an attacker get access to the communication system and find information contained within secret data. These attacks are difficult to intercept because the attacker do not change the contents of the original data. On the other hand, in active attack an attacker not only gets access to the data but also disrupt the original data. The active attacks are easily detectable but difficult to recover. Organizations cannot rely on the original form of their secret data and they even don‘t want any attacker to launch the passive attack (active attack is more harmful) against their communication/ information system. So, they use encryption schemes usually known as cipher (encryption algorithm) in the field of cryptography. Some ciphers e.g. Data Encryption Standard (DES), Advance Encryption Standard (AES) uses secret keys to encrypt the secret data/ message or plaintext. Ant-Crypto is a novel swarm based attack for the cryptanalysis of DES. Cryptanalysis is about the techniques in cryptography that tries to recover the original message or plaintext from an encrypted message, without knowing the secret key used during encryption phase. It includes the study of mathematical techniques e.g. linear cryptanalysis and differential cryptanalysis for attacks against communication/ information system security. There are two types of ciphers based on the unit of a plaintext that goes under processing; first, the Block ciphers and second, the Stream ciphers. Block ciphers are modern ciphers and operates on a block or chunk of the original plaintext using fixed transformation based on the combination of substitution and permutation. Stream ciphers process a single byte of a message at a time when en/decrypting. DES is based on feistel block cipher. Substitution ciphers are easily breakable due to their weedy encryption process [13]. The length of the key is the main indicator of how difficult it would be to break a cipher. DES with a 56 bit key length makes brute force attack infeasible as it would take several years to find the secret key even if the original plaintext is known. In the next section, we will review the related work in the domain of DES cryptanalysis. IJCSI International Journal of Computer Science Issues, Vol. 10, Issue 1, No 1, January 2013 ISSN (Print): 1694-0784 | ISSN (Online): 1694-0814 www.IJCSI.org 400 Copyright (c) 2013 International Journal of Computer Science Issues. All Rights Reserved.