In the description of quantum key distribution systems, much attention is paid to the operation of quantum cryptography protocols. The main problem is the insufficient study of the synchronization process of quantum key distribution systems. This paper contains a general description of quantum cryptography principles. A two-line fiber-optic quantum key distribution system with phase coding of photon states in transceiver and coding station synchronization mode was examined. A quantum key distribution system was built on the basis of the scheme with automatic compensation of polarization mode distortions. Single-photon avalanche diodes were used as optical radiation detecting devices. It was estimated how the parameters used in quantum key distribution systems of optical detectors affect the detection of the time frame with attenuated optical pulse in synchronization mode with respect to its probabilistic and time-domain characteristics. A design method was given for the process that detects the time frame that includes an optical pulse during synchronization. This paper describes the main quantum communication channel attack methods by removing a portion of optical emission. This paper describes the developed synchronization algorithm that takes into account the time required to restore the photodetector’s operation state after the photon has been registered during synchronization. The computer simulation results of the developed synchronization algorithm were analyzed. The efficiency of the developed algorithm with respect to synchronization process protection from unauthorized gathering of optical emission is demonstrated herein.

The synchronization a two pass self-compensation quantum key distribution system (QKDS) with phase-encoded photon states are reviewed. A modified algorithm for synchronizing a two pass self-compensation QKDS with phase-encoded photon states was proposed. The first is the emphasis on the implementation in the single-photon mode which improves the synchronization mode security. The second peculiarity is that in case the number of accumulated impulses in two adjacent time windows is equal, it is decided to receive a photon impulse by any of these windows, if the number of accumulated impulses exceeds the number of measured dark current pulses (DCP) in the rest of the windows. In the known algorithm in such a case both windows were taken as noise which was the reason of the signal window skip. An analytical expression for the correct detection probability calculation of the photon impulse receipt in the algorithm proposed for the sync initialization of the QKDS.

A two-pass auto-compensation fiber-optic quantum key distribution system (QKDS) with phase-encoded photon states in synchronization mode has been investigated. Preliminary stage sync initialization algorithm of QKDS that requires impulse-repetition period division into time windows as well as signal time window detection has been proposed. The peculiarity of the algorithm being investigated is that it is implemented in the single-photon mode which improves the synchronization mode security. The second peculiarity is that in case the number of accumulated impulses in two adjacent time windows is equal, it is decided to receive a photon impulse by any of these windows, if the number of accumulated impulses exceeds the number of registered impulses in the rest of the windows. Algorithm modeling has discovered that when the number of time windows is changed from 2 to 100000 probabilities limit values difference does not exceed 0.5 %. Requirements of time window duration ratio to the photon impulse have been formulated. It has been demonstrated that when the number of time windows is increased from 2 to 1024 the probability reduces by less than 1.5 % in case of time uncertainty decrease in respect to the photon impulse occurrence in 512 times. An analytical expression for computation of a signal time window correct detection probability in the proposed algorithm of the preliminary stage QKDS synchronization.

Continuous-variable quantum key distribution (CV-QKD) with a real local oscillator (LO) experiences a phase attack security challenge due to the reference pulses transmitted along with quantum signals over an unsecure quantum channel. In this paper, a phase attack on reference pulses of CV-QKD with a real LO is investigated. The performance of the discrete-modulated (DM) CV-QKD under this attack is analyzed analytically and by simulation, and compared with the Gaussian-modulated (GM) CV-QKD. It is found that such an attack by an eavesdropper's, significantly reduce the transmission distance for the GM based CV-QKD, whereas, the DM based CV-QKD shows a high tolerance to high phase noise. Based on phase attack monitoring, a new adaptive modulation scheme is proposed for CV-QKD to adaptively switch between GM and DM so as to maintain the optimum secret key rate.

The two pass auto compensation quantum key distribution system (QKDS) with phase-encoded states of photons in synchronization mode are studied. The algorithm of synchronization QKDS, presupposing the division of the repetition period of the optical pulses on the time windows and the detection of the signal window are offered. The peculiarity of the algorithm is that it is implemented in the single-photon mode, increasing the security of synchronization mode. The second feature of the algorithm is that when equal numbers of accumulated pulses in two adjacent time windows, a decision for admission photon pulse in any of the windows, if the number of accumulated pulses in it exceeds the number of detected pulses in the other windows. In a certain algorithm in this case, both windows were “noises” that was the reason for missing the signal window. Modeling algorithm found that when the number of time windows from 2 to 1024, the difference of the limiting values of the probability does not exceed 3.34%. The requirements with respect to the duration of the time window and the photon momentum are formulated. It is shown that increasing the number of time windows from 2 to 1024 implies reducing the probability of less than 2% while maintaining the time of uncertainty in relation of emergence the photon pulse 512 times. An analytical expression for the calculation of the probability of correct detection of the signal time window in the proposed synchronization algorithm QKDS.

This paper describes trends in the field of encryption, based on the principles of quantum cryptography. Here is a description of commercial self-compensation quantum key distribution system (QKDS). A description of quantum-cryptographic network stand, based on integrated commercial QKDS Clavis2 from idQuantique (Switzerland), is also proposed. Research of quantum key integration into telecommunication data transmission network encryption protocol is offered. Capabilities of quantum-cryptographic network stand are also formulated.