I. Introduction
Quantum key distribution is the latest technology that solves the problem of key distribution for symmetric encryption systems using optical fiber as the propagation medium [1]–[3]. The systems of quantum key distribution offered now in the market implement a protocol stack, which consists of both information transfer protocol by single photons, and procedures realizing privacy amplification. These procedures allow to distribute securely an encryption key even in the presence of unauthorized connection to a communication channel if the level of the errors generated by interception in the channel does not exceed some threshold. However, these systems are intended to distribute keys between single pairs of users and have a high market value.