Improved White-box SM4 Design and Implementation

SM4, as a block cipher standard in China, has received extensive attention since the date of its publication. Its implementation correctness and security have rapidly become a research hotspot. With the popularity of cryptographic algorithms in network security, attack methods such as key whitening attack, software static analysis, and reverse engineering in the software implementation environment are also constantly developing. In order to resist these attack methods, a white-box implementation of the key in the cryptographic algorithm is required. Common white-box implementation schemes add a large number of linear or nonlinear transformations, which greatly reduces the implementation efficiency while enhancing the security. In this paper, we optimized the white-box design method of Xiao-Lai SM4 algorithm. According to its structural characteristics, we reduced one affine transformation and increased nonlinear encoding without disclosing the relevant information of intermediate data. Also, our work distinguished the implementation of the first, intermediate and last rounds. We operated the simulation implementation, and the implementation efficiency is significantly improved. Then the white-box diversity and white-box ambiguity in the optimized scheme are calculated, which proves the security of the optimized algorithm. After the correctness and implementation efficiency tests, the encryption speed is improved by 18.6% and the decryption speed is improved by 20.8% compared with the original scheme.