Weak-key classes of 7-round MISTY 1 and 2 for related-key amplified boomerang attacks

초록

In 1997, M. Matsui proposed secret-key cryptosystems called MISTY 1 and MISTY 2, which are 8- and 12-round block ciphers with a 64-bit block, and a 128-bit key. They are designed based on the principle of provable security against differential and linear cryptanalysis. In this paper we present large collections of weak-key classes encompassing 2(73) and 2(70) weak keys for 7-round MISTY 1 and 2 for which they are vulnerable to a related-key amplified boomerang attack. Under our weak-key assumptions, the related-key amplified boomerang attack can be applied to 7-round MISTY 1 and 2 with 2(54), 2(56) chosen plaintexts and 2(55.3) 7-round MISTY 1 encryptions, 2(65) 7-round MISTY 2 encryptions, respectively.

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