An attack on 5.5-round IDEA

In this paper, we describe the attacks on IDEA. IDEA is a 64-bit block cipher with 128-bit keys which proposed by Xuejia Lai and Massey in 1991. First we use simple sentences to describe the general idea of IDEA. Then we devise a new attack on 5.5-round IDEA. Although there are many attacks on the reduced-round cipher, there is no successful attack has been found on the complete cipher.