Integral cryptanalysis: a new key determination technique for 3-phase Kuznyechik encryption

The primary objective of this work is to develop an algorithm for detecting the secret round key used in encryption by analyzing a collection of plaintexts and ciphertexts encrypted with the three-round Kuznyechik algorithm. In addition, the fundamentals of using the integral cryptanalysis method for the Substitution-permutation (SP) network-based Kuznyechik encryption have been investigated. It has been found that the Kuznyechik three-round encryption algorithm is useful for creating a balanced set before the third round and an unbalanced set at the end of the round, using a set in which the first byte is active, and the remaining bytes are passive. Based on the findings above, an efficient algorithm to determine the key of the final round for the 3-round Kuznyechik algorithm is proposed utilizing the method of integral cryptanalysis. According to simulation results, the proposed approach offers approximately 90% improvement compared to baseline algorithms in terms of time complexity, data, and memory overhead.