On tweaking dual MISTY-TYPE blockciphers

Tweakable blockciphers are blockciphers with an additional input, the tweak, that is used to provide variation, but is not kept secret. An open problem proposed by Liskov et al.is how to construct tweakable blockciphers without using a preexisting blockcipher. In this paper, on the basis of four round Dual MISTY-TYPE transformations, we propose a tweakable blockcipher directly and solve the above open problem. The new scheme is provable security if the underlying block cipher is a pseudorandom permutation. At the same time, we point out that there is no secure tweakable blockcipher on the basis of three round Dual MISTY-TYPE transformations.