Round security and super-pseudorandomness of MISTY type structure

Abstract

The security of an iterated block cipher heavily depends on its structure as well as each round function. Matsui showed that MISTY type structure is faster and more robust than Feistel structure on linear cryptanalysis and differential cryptanalysis. On the other hand, Luby and Rackoff proved that the four round Feistel structure is superpseudorandom if each round function fi is a random function. This paper proves that the five round MISTY type structure is super-pseudorandom. We also characterize its round security.