Phase-reference intensity attack on continuous-variable quantum key distribution with a real local oscillator

TL;DR

This paper identifies a security vulnerability in practical LLO CV-QKD systems caused by unmonitored phase-reference pulse intensity, proposes attack strategies exploiting this loophole, and suggests intensity monitoring as a countermeasure to enhance security.

Contribution

It introduces practical attack strategies on phase-reference pulse intensity in LLO CV-QKD and proposes an intensity-monitoring scheme to improve system security.

Findings

Attack strategies can reduce trusted phase noise without detection.

Real-time intensity monitoring prevents the proposed attacks.

The proposed scheme enhances the robustness of the security model.

Abstract

In practical continuous-variable quantum key distribution system using local local oscillator (LLO CV-QKD), the phase noise related to coherent detection and phase-reference pulse intensity that can be locally calibrated at the receiver side is considered to be trusted noise to improve the performance. However, if the intensity of the phase-reference pulse is not monitored precisely in real-time, a security loophole will be opened for the eavesdropper to launch attacks. To this end, we propose two practical phase-reference pulse intensity attack strategies, where Eve can reduce the trusted phase noise by manipulating the intensity of the phase-reference pulse, thereby hiding her attack on the signal pulse if the total excess noise remains unchanged. The performance of the LLO CV-QKD system under these attacks has been analyzed. We show that precisely monitoring the intensity of the phase-reference pulse in real-time is an essential countermeasure to prevent the proposed attacks. Moreover, an intensity-monitoring scheme for the phase-reference pulse is proposed to strengthen the security of the practical LLO CV-QKD system and make the trusted phase noise model more robust.