Background. Modern data transmission systems using cryptographic methods of information protection require high reliability and quality of information transmission. The object of research is protected data transmission systems. The subject of research is various ways to correct errors in the communication channel. The purpose of this work is to develop an algorithm for restoring the synchronization of the cipher and gamma when decrypting, after transmitting a message over a communication channel with interference, using the properties of convolutional codes. Materials and methods. The study was conducted using the Matlab environment. Models of convolutional code decoder using the Viterbi algorithm. Results. An algorithm and a block diagram of a device that implements the restoration of synchronization of the cipher and gamma when decrypting a message, after passing a communication channel with interference, have been developed. Conclusions. The effect of distortion such as bit loss on a message transmitted over a communication channel with interference can lead to desynchronization of the cipher and gamma when decrypting the message. Analysis of the message decoding process using the Viterbi algorithm will make it possible to detect and eliminate this type of interference.