The article is focused on research of an attack on the quantum key distribution system and proposes a countermeasure method. Particularly noteworthy is that this is not a classic attack on a quantum protocol. We describe an attack on the process of calibration. Results of the research show that quantum key distribution systems have vulnerabilities not only in the protocols, but also in other vital system components. The described type of attack does not affect the cryptographic strength of the received keys and does not point to the vulnerability of the quantum key distribution protocol. We also propose a method for autocompensating optical communication system development, which protects synchronization from unauthorized access. The proposed method is based on the use of sync pulses attenuated to a photon level in the process of detecting a time interval with a signal. The paper presents the results of experimental studies that show the discrepancies between the theoretical and real parameters of the system. The obtained data allow the length of the quantum channel to be calculated with high accuracy.

中文翻译：

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对量子密钥分发系统的非经典攻击

本文着重研究对量子密钥分发系统的攻击，并提出了一种对策方法。特别值得注意的是，这并不是对量子协议的经典攻击。我们描述了对校准过程的攻击。研究结果表明，量子密钥分发系统不仅在协议中存在漏洞，而且在其他重要系统组件中也存在漏洞。所描述的攻击类型不会影响接收到的密钥的加密强度，也不会指出量子密钥分发协议的脆弱性。我们还提出了一种用于自动补偿光通信系统开发的方法，该方法可以保护同步免受未经授权的访问。所提出的方法基于在检测信号的时间间隔的过程中使用衰减到光子水平的同步脉冲。本文介绍了实验研究的结果，这些结果表明了该系统的理论参数与实际参数之间的差异。所获得的数据允许以高精度计算量子通道的长度。