The purpose of this work is to develop and research a hybrid encryption algorithm based on the joint application of the symmetric encryption algorithm Kuznyechik and homomorphic encryp-tion (Gentry scheme or BGV scheme). Such an encryption algorithm can be useful in situations with limited computing resources. The point is that with the correct expression of the basic operations of the symmetric encryption algorithm through Boolean functions, it becomes possible on the transmitting side to encrypt the data with a symmetric cipher, and the secret encryption key - with a homomorphic one. In this case, manipulations can be carried out on the receiving side so that the original encrypted message is also encrypted only with a homomorphic cipher. In this case, symmetric encryption is removed, but the information remains inaccessible to the node that pro-cesses it. This property of secrecy makes it possible to carry out resource-intensive operations on a powerful computing node, providing homomorphically encrypted data for a low-resource node for the purpose of their subsequent processing in encrypted form. The article presents the developed hybrid algorithm. As a symmetric encryption algorithm, Kuznyechik encryption algorithm is used, which is part of the GOST R34.12 - 2015 standard. In order to be able to apply homomorphic encryption to data encrypted with the Kuznyechik cipher, the Kuznyechik algorithm S-boxes is presented in a boolean form using the Zhegalkin polynomial. Also, the linear transformation L is presented in the sequence form of performing the simplest operations of addition and multiplication on the transformeddata. The primary modeling of the developed algorithm was carried out on a simplified version of the KuzchyechikS-KN1 algorithm.
