Differential analysis of three rounds of cipher «Kuznyechik»

Annotation: «Kuznyechik» is a new symmetric encryption algorithm, adopted as an encryption standard GOST R 34.12–2015, built on the principle of SP-network. There are still no publications on the differential properties of the algorithm «Kuznyechik». In this paper, the properties of the main operations are re- searched and described, and a method of differential analysis of three rounds of the algorithm of encryption «Kuznyechik» is proposed. In the issue of the investigation of the differential properties of the nonlinear function S and linear function L, it was established that a 1 non-zero byte of the difference as a result of the function L can be expanded into 16 non-zero bytes, passes through the replacement block S, and then folded again into 1 nonzero byte. The developed scheme allows to affect the active S-unit a minimum number of times. Thus, the overall complexity of the analysis, including searching for the correct pairs of texts and searching for bits of the secret en- cryption key is 2 108 + 6 * 2 120 encryptions.

Keywords: cryptography, block cipher, sp-network, crypt- analysis, differential cryptanalysis, cipher «kuznyechik», gost r 3412-2015