González-Payo Javier, Trényi Róbert, Wang Weilong, Curty Marcos
Escuela de Ingeniería de Telecomunicación, Department of Signal Theory and Communications, University of Vigo, Vigo E-36310, Spain.
State Key Laboratory of Mathematical Engineering and Advanced Computing, Zhengzhou, Henan 450001, China.
Phys Rev Lett. 2020 Dec 31;125(26):260510. doi: 10.1103/PhysRevLett.125.260510.
The performance of quantum key distribution (QKD) is severely limited by multiphoton pulses emitted by laser sources due to the photon-number splitting attack. Coherent-one-way (COW) QKD has been introduced as a promising solution to overcome this limitation, and thus extend the achievable distance of practical QKD. Indeed, thanks to its experimental simplicity, the COW protocol is already used in commercial applications. Here, we derive simple upper security bounds on its secret key rate, which demonstrate that it scales at most quadratically with the system's transmittance, thus solving a long-standing problem. That is, in contrast to what has been claimed, this approach is inappropriate for long-distance QKD transmission. Remarkably, our findings imply that all implementations of the COW protocol performed so far are insecure.
由于光子数分裂攻击，激光源发射的多光子脉冲严重限制了量子密钥分发（QKD）的性能。相干单向（COW）QKD作为一种有前景的解决方案被引入，以克服这一限制，从而扩展实际QKD可实现的距离。事实上，由于其实验简单性，COW协议已被用于商业应用。在此，我们推导了其密钥率的简单上界安全性，这表明它最多与系统的透射率成二次方比例缩放，从而解决了一个长期存在的问题。也就是说，与所声称的情况相反，这种方法不适用于长距离QKD传输。值得注意的是，我们的发现意味着迄今为止执行的所有COW协议实现都是不安全的。
