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 supper-pseudorandom if each round function f_i is a random function. This paper proves that the five round MISTY type structure is super-pseudorandom. We also characterize its round security.
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