Attacking Reduced-Round Versions of the SMS4 Block Cipher in the Chinese WAPI Standard

SMS4 is a 32-round block cipher with a 128-bit block size and a 128-bit user key. It is used in WAPI, the Chinese WLAN national standard. In this paper, we present a rectangle attack on 14-round SMS4, and an impossible differential attack on 16-round SMS4. These are better than any previously known cryptanalytic results on SMS4 in terms of the numbers of attacked rounds.

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