An Approach to Avoid Meet in the Middle Attack in 2 DES

Abstract

Cryptography is evolving with new and better algorithms. The existing DES provides security but is vulnerable on account of its smaller key. An attacker can easily break through DES with a minimal number of operations. 2 DES or double DES uses a longer key but is highly vulnerable due to Meet in the middle attack, which reduces the brute force time by almost a factor of 2. In this paper, we introduce a better algorithm that incorporates the best features from DES and 2 DES. The new algorithm is essentially a modified version of DES. It is operational over blocks of size 128 bits. The key used is of 112 bits and thus ensuring better security over DES. We use single encryption, unlike 2 DES that uses double encryption, ensuring edge over Meet in the Middle attack. The algorithm makes use of the Feistel cipher algorithm. The plaintext is divided into blocks of size 128 bits. Each block is further divided into two sub-blocks say L and R 64 bits each. We divide these L and R blocks again, say L0 and R0 (from L), and L’0 and R’0 (from R). In the next step, we perform Feistel cipher over L0 and R’0 on one hand and L’0 and R0 on the other. Multiple divisions and inter Feistel between left and right blocks ensures better mixing and provides a better avalanche effect. Everything combined ensures better security of the plaintext involved.