New Linear Cryptanalysis of Chinese Commercial Block Cipher Standard SM4

Abstract EN

SM4 is a Chinese commercial block cipher standard used for wireless communication in China.

In this paper, we use the partial linear approximation table of S-box to search for three rounds of iterative linear approximations of SM4, based on which the linear approximation for 20-round SM4 has been constructed.

However, the best previous identified linear approximation only covers 19 rounds.

At the same time, a linear approximation for 19-round SM4 is obtained, which is better than the known results.

Furthermore, we show the key recovery attack on 24-round SM4 which is the best attack according to the number of rounds.