An important scientific and practical problem of ensuring the effectiveness of crypto-steganographic systems in real time on resource-limited platforms has been solved by developing an appropriate scientifically based methodology, focused on code control of cryptographically protected additional information embedding in the spatial domain of the container. In the dissertation relationship between the transformants of the two dimensional, one-dimensional Walsh-Hadamard transform and the discrete cosine transform, as well as the components of the singular value decomposition of the container block, is established, based on which formal sufficient conditions for the given properties of the steganographic message are obtained, and the theoretical foundations for the formation of steganographic methods with code control are developed. The theoretical basis for the synthesis of effective codewords was formed, as well as indicators of energy and selectivity of the codeword were introduced and researched, which made it possible to synthesize multi-level codewords, which ensure the effectiveness of steganographic methods with code control developed on their basis. Two steganographic methods with code control of additional information embedding using binary and multi-level codewords have been created, which ensures their effectiveness, which exceeds modern analogs, in particular, in the conditions of a streaming container. Using the developed theoretical basis, Reed-Solomon codes, and the developed codes of spatial arrangements, two steganographic methods with multiple access are proposed, which allow, while preserving the advantages of code control, to support the registration in the system of up to several thousand users and the simultaneous operation of several tens of users. In the context of increasing the cryptographic strength of crypto-steganographic systems, the theoretical basis for ensuring the cryptographic quality of many-valued logic functions was built, which includes the following criteria: algebraic nonlinearity, distance nonlinearity, the avalanche effect criterion, the criterion of output independence from input variables, which made it possible to implement a justified choice of many-valued logic functions for the tasks of building specialized block symmetric ciphers for encrypting the states list sequence when using the steganographic method with code control of the additional information embedding. Based on the developed cryptographic quality criteria for many-valued logic functions, the sets of S-boxes of practically valuable lengths have been synthesized that have the maximum possible level of nonlinearity of both component Boolean functions and component many-valued logic functions, satisfy the error propagation criterion of the highest orders, and are also optimal in terms of the criterion of independence of the output of the component many-valued logic functions from their input variables, which makes it possible to increase the cryptographic quality of cipher constructions used in crypto-steganographic systems. Ready for practical implementation block symmetric cipher has been developed, the use of which allows to accelerate the destruction of the statistics of the plaintext, which made it possible to reduce the number of necessary iterations of the main step of cryptographic transformation, and, therefore, the computational costs for the operation of preliminary encryption of additional information in the preliminary coder of the crypto-steganographic system. The practical value of the manuscript consists in bringing the obtained scientific results to specific methods and algorithms that can be applied in practical information protection systems, including those that involve deployment on resource-limited platforms and require operation with streaming containers in real-time mode. Algorithmic implementations of steganographic methods with code control of information embedding are characterized by realization simplicity, as well as the flexibility of setting properties of steganographic message by certain codewords choosing.
