Two Simplified Versions of Kuznyechik Cipher (GOST R 34.12-2015)

Kuznyechik cipher is a new symmetric block cipher declared as a state standard in Russian Federation. The cipher is based on SP (Substitution Permutation) network principle, the block size is 128 bits, the key size is 256 bits, and encryption takes nine rounds. Round subkeys are generated from the original secret master key with Feistel scheme. Many modern standard including DES and AES have simplified versions. These versions can be used in education in order to demonstrate encryption and decryption operations to students. In addition to that, simplified versions are used for simulation of various attack scenarios and cryptanalysis methods. In this paper we propose two simplified versions of Kuznyechik algorithm. The first one is extremely simple and can be used in education. All transformations can even be performed manually in reasonable time. The second version is more complicated. This one is designed for simulation of different types of attacks and we offer it for the demonstration of Kuznyechik's basic principles.