Abstract:

As a candidate of AES, E2 algorithm has attracted wide attention because of its unique two SP structures. We evaluate the security of E2 block cipher against meet-in-the-middle attacks. Based on the idea of meet-in-the-middle, by analyzing the feathers of E2 algorithm, a 4-round distinguisher is designed. Using the distinguisher, some meet-in-the-middle attacks are made on 5/6round E2128/256. It is shown that the E2-128 algorithm to 5-round and the E2-256 algorithm to 6-round are not immune to meet-in-the-middle attacks. This is the first time to use the meet-in-the-middle attacks to analyze the E2 algorithm. Compared with  the existing results, data complexity is reduced.

Key words: block cipher;meet-in-the-middle attack;E2;attack complexity