Security Enhancement in Data Encryption Standard

Abstract

Data Encryption Standard (DES) is the most widely used cryptosystem. Faster computers raised the need of high security cryptosystems. Due to its small key length and simple feistel network, many cryptanalysts developed various methods, like parallel and exhaustive attack, to break DES. DES is most vulnerable to differential cryptanalysis attack. This paper proposes modifications in DES to ensure security enhancement by improving the key length and the weak round function against cryptographic attacks. We show analytically that the modified DES is stronger against cryptographic attacks. The proposed modifications divide the expanded 48 bits of right block into two equal blocks of 24 bits. Then two different functions are performed on these two blocks. The effective key length is increased to 112 bits by using 2 keys. These two keys are used in special sequence with round numbers. The analysis shows that for the proposed approach, the probability of characteristic for differential cryptanalysis is reduced and the unicity distance is better as compared to standard DES.