METHODOLOGY FOR FORMING A HIGH-SPEED IMITATOR-RESISTANT CIPHER FOR MULTI-ALPHABET SUBSTITUTION

Abstract

The article considers the problems and tasks of forming requirements for the construction of a high-speed imitation-resistant multi-alphabet substitution cipher based on the principles of rotary systems, which is relevant in terms of ensuring cybersecurity of critical infrastructure facilities with an increased risk of disruption of stable operation. The ontological model of the functional security entities of automated process control systems (APCS) at critical infrastructure facilities (CIF) is analysed. It is determined that the tools for improving functional security in this case should be measures and means of cyber defence aimed at preventing the implementation of threats of interception, analysis and imitation of critical technological information and ensuring the adjustment of the chosen security policy. It is emphasised that an important component of the functional security of systems and complexes of critical infrastructure facilities is the protection of critical technological information during its transmission via public communication channels. An effective mechanism for counteracting these threats is the use of a multi-alphabet substitution cipher, for which purpose a corresponding model is proposed, based on the mathematical principles of constructing rotary encryption systems, which, within the framework of the model, are devoid of their inherent vulnerabilities. The model provides a two-stage transformation of open data using data from a pseudorandom sequence generator, which is a modified model of the A5/1 algorithm that has the necessary functional and cryptographic characteristics. The considered factors of ensuring the cryptographic security of the proposed model allowed us to reasonably propose a high-speed solution for calculating the message authentication code directly in the encryption process.