Lai Massey(L M) is one of the most important structures used in block ciphers. But it’s not pseudorandom with any given rounds. By a simple transform, S.Vaudenay got the transformation of L M scheme, which is preudorandom and used in FOX. This paper researched the design of tweakable blockciphers based on the transformation of L M structure. The feasibility to design block ciphers by XORing a tweak value into different places in the dataflow of the 3 round L M transformation was analyzed. The attack methods for 3 round transformation were given.
