Pseudorandomness of MISTY-type transformations and the block cipher KASUMI

Abstract

We examine the security of block ciphers on the view point of pseudorandomness. Firstly we show that the four round (unbalanced) MISTY-type and the three round dual MISTY-type transformations are pseudorandom permutation ensembles. Secondly we prove that the three round KASUMI is not a pseudorandom permutation ensemble but the four round KASUMI is a pseudorandom permutation ensemble. We provide simplified probability-theoretic proofs for non-adaptive distinguishers.