Development of Methods for Improving Crypto Transformations in the Block-Symmetric Code

The development of modern technologies and the emergence of full-scale quantum computers requires a critical revision of the requirements for the level of algorithms cryptographic stability, both post-quantum cryptography, and used in cyberspace and information and communication systems algorithms of traditional and asymmetric cryptography. The analysis of possible approaches to increase the level of cryptographic stability of symmetric cryptography algorithms based on Feistel chains. One of the promising algorithms of symmetric cryptosystems in the conditions of post-quantum cryptography (post-quantum period) according to experts is the algorithm GOST 28147-2009 (DSTU GOST 28147: 2009, GOST R-3412 -2015) the main advantages of which is the simplicity of implementation and high level crypto stability. However, in a full-scale quantum computer, the effectiveness of cryptographic information security based on symmetric cryptosystems (their level of crypto-stability) can be called into question by the possibility of an attack based on Grover's algorithm, which is easy to use to find the encryption key by brute-force. Methods of increasing the cryptographic stability of block-symmetric algorithm GOST 28147-2009 (DSTU GOST 28147: 2009, GOST R-3412 2015) are proposed by increasing the key sequence (by increasing the length of S-blocks), and/or by increasing the number of S- blocks, which increases the level of crypto stability and counteracts a “brute force” attack based on a quantum computer. To confirm the proposed methods of increasing the level of crypto-stability of the symmetric algorithm GOST 28147-2009 (DSTU GOST 28147: 2009), the results of the complexity of operations in the integer ring, expressed in the operations of the processor, which confirms the possibility of implementation of this algorithm without significant increase in energy consumption elementary group operations).