A Lightweight Nonlinear White-Box SM4 Implementation Applied to Edge IoT Agents

The white-box implementation of cryptography algorithm can hide key information even in the white-box attack context owing to the means of obfuscation. However, under the deliberately designed attack, there is still a risk of the information being recovered within a certain time complexity. In this paper, a lightweight nonlinear white-box SM4 implementation is proposed to prevent several typical attacks from extracting the secret key, which hides the encryption and decryption process in obfuscated lookup tables. Aiming to improve the diversity and ambiguity of the lookup tables as well as resist the different types of white-box attacks, the random bijective nonlinear mappings are applied as scrambling encodings of the lookup tables. Moreover, the memory occupation of the implementation doesn't increase significantly by simplifying the structure and using concatenation code. Through several quantitative indicators, including memory size, diversity, ambiguity, the time complexity required to extract the key, and the value space of the key and external encodings, it is proved that the security of the proposed implementation could been enhanced significantly, while no sacrificing the practicality, compared with the existing schemes.