On Super-Psudorandomness of MISTY-Type Tweakable Blockciphers

Abstract

An open problem about tweakable blockcipher proposed by Liskov et al. is how to construct tweakable blockciphers without using pre-existing blockcipher. In this paper, on the basis of MISTY-Type transformation, we perform a systematic study of the open problem. We analyze the approach of including a tweak by XORing the tweak value into one place in the dataflow of the MISTY-Type structure. We mainly discuss the super-pseudo randomness of the structure. We conclude that the 5 round MISTY-Type tweakable blockciphers are not CCA-secure and there exists CCA-secure 6 round MISTY-Type tweakable blockciphers. Finally, we give the concrete cryptanalysis for the CCA-secure 6 round MISTY-Type tweakable blockciphers.