This paper represents a developed cryptographic information protection algorithm based on a substitutionpermutation network. We describe the cryptographic transformations used in the developed algorithm. One of the features of the algorithm is the simplicity of its modification with regard to different security levels. The algorithm uses a predeveloped S-box tested against differential and linear cryptanalysis. The S-box is consistent with one of the known standards AES and GOST R 34.12-2015. We provide the findings of an avalanche-effect investigation and statistical properties of ciphertexts. The algorithm actually meets the avalanche-effect criterion even after the first round.