Abstract
The employees of the Information Security Laboratory have developed the AL04 cryptographic algorithm based on nonlinear substitution blocks and a round key scheduling mechanism. This symmetric block encryption algorithm is designed to achieve an optimal balance between security, computational efficiency and low resource consumption, with the aim of using it to protect voice information transmitted over high-frequency (HF) radio channels.To evaluate the cryptographic strength of the AL04 algorithm, well-known cryptanalysis methods were used. In addition, the output data of the algorithm were evaluated for randomness using NIST and Donald Knuth statistical tests. The results showed that the encrypted data generated by AL04 correspond to random data. The AL04 algorithm and its S-boxes were analyzed for the avalanche effect. As a result, the obtained data demonstrate a strong avalanche effect, which indicates high sensitivity to changes in input data and ensuring cryptographic strength.