International Association for Cryptologic Research (IACR)
Abstract
SMS4 is a 128-bit block cipher used in the
WAPI standard for wireless networks in China. In this paper, we
analyze the security of SMS4 block cipher against differential
cryptanalysis. Firstly, we prove three theorems and one corollary
that reflect relationships of 5- and 6-round SMS4. Nextly, by
these relationships, we clarify the minimum number of differentially
active S-boxes in 6-, 7- and 12-round SMS4 respectively.
Finally, based on the above results, we present a family of about
214 differential characteristics for 19-round SMS4, which
leads to an attack on 23-round SMS4 with 2115 chosen
plaintexts and 2124.3 encryptions. Our attack is the best known
attack on SMS4 so far