Practical Attack on the Full MMB Block Cipher

摘要

Modular Multiplication based Block Cipher (MMB) is a block cipher designed by Daemen et al. as an alternative to the IDEA block cipher. In this paper, we give a practical sandwich attack on MMB with adaptively chosen plaintexts and ciphertexts. By constructing a 5-round sandwich distinguisher of the full 6-round MMB with probability 1, we recover the main key of MMB with text complexity 2~(40) and time com plexity 2~(40) MMB encryptions. We also present a chosen plaintexts attack on the full MMB by employing the rectangle-like sandwich attack, which the complexity is 2~(66.5) texts, 2~(66.5) MMB encryptions and 2~(70.5) bytes of memory. In addition, we introduce an improved differential attack on MMB with 2~(96) chosen plaintexts, 2~(96) encryptions and 2~(66) bytes of memory. Especially, even if MMB is extended to 7 rounds, the improved differential attack is applicable with the same complexity as that of the full MMB.