Practical implementations of quantum key distribution systems use attenuated laser pulses as the signal source rather than single photons . the channels used to transmit are lossy . on the basis of above two points , a combining eavesdropping strategy of intercept - resend and beam - splitting is discussed in terms of eavesdropper ' s technology requirement and detection efficiency and dark count of single - photon counter 主要工作包括以下三部分：一、基于实际量子密钥分配( qkd )系统中所使用的强衰减的激光脉冲不是单光子，量子密钥分配的信道不是无损耗的，光子计数器存在探测效率和暗计数以及窃听者的技术能力也不是无限的这些具体问题。
We adopt double alkali cathodal tube 9789qb , which was made by emi corporation in england , as our photomultiplier , whose spectrum ranges between 300nm to 650nm , with less noise counters and single - photon apices , which make it suitable as a single - photon - counter . the disparted - voltage device is designed in a reasonable way and the cooling system of iquefied nitrogen which makes it small in size , simple in structure , easy in processing , cheap in cost and good in performance 该管型的光谱范围在300 650nm ，具有暗计数少，有单光子峰的特点，适于做单光子计数器；本文的光电倍增管分压器设计合理而冷却系统采用液氮，该系统体积小、结构简单、加工便利、成本低廉且性能良好。
