Local oscillator fluctuation opens a loophole for Eve in practical continuous-variable quantum-key-distribution systems

TL;DR

This paper reveals that fluctuations in the local oscillator in practical continuous-variable quantum key distribution systems create a security loophole that an eavesdropper can exploit, significantly compromising the secret key rate.

Contribution

It identifies a new security vulnerability caused by LO fluctuations and demonstrates the importance of monitoring LO intensity for secure quantum communication.

Findings

LO fluctuations can be exploited by Eve to hide attacks

Failure to monitor LO intensity reduces secret key rate

Numerical simulations confirm security risks

Abstract

We consider the security of practical continuous-variable quantum key distribution implementation with the local oscillator (LO) fluctuating in time, which opens a loophole for Eve to intercept the secret key. We show that Eve can simulate this fluctuation to hide her Gaussian collective attack by reducing the intensity of the LO. Numerical simulations demonstrate that, if Bob does not monitor the LO intensity and does not scale his measurements with the instantaneous intensity values of LO, the secret key rate will be compromised severely.