Abstract
Considering that cryptographic algorithms are among the most reliable methods for protecting information in information systems, assessing their cryptographic strength plays a significant role. For this purpose, comprehensive studies are conducted, and one of the primary characteristics of such an assessment is the statistical security of the obtained ciphertexts. This article investigates the statistical security of the block cipher algorithm AL04, developed in the Information Security Laboratory. The algorithm was implemented in software, and the resulting ciphertexts were analyzed using the test sets of D. Knuth and NIST, as well as checked against the avalanche effect criterion (average number of output bits, degree of completeness, degree of avalanche effect, degree of strict avalanche criterion). The statistical tests used are the main tests in the works of many researchers and determine the properties of sequence randomness with high accuracy. The study found that AL04 does not have deviations in the sequences obtained using the algorithm. Thus, it was established that the algorithm possesses high statistical security.