Effect of light injection on the security of practical quantum key distribution

TL;DR

This paper investigates how external light injection can compromise the security of practical quantum key distribution systems by exploiting vulnerabilities in LiNbO3 optical modulators, demonstrating experimental risks and proposing countermeasures.

Contribution

It identifies a new security vulnerability in LiNbO3-based optical modulators used in QKD and experimentally demonstrates how external light injection can be exploited to threaten system security.

Findings

External light injection affects LiNbO3 modulators' performance.

Eavesdroppers can control quantum state intensities.

Countermeasures can mitigate the security risks.

Abstract

Quantum key distribution (QKD) based on the fundamental laws of quantum physics can allow the distribution of secure keys between distant users. However, the imperfections in realistic devices may lead to potential security risks, which must be accurately characterized and considered in practical security analysis. High-speed optical modulators, being as one of the core components of practical QKD systems, can be used to prepare the required quantum states. Here, we find that optical modulators based on LiNbO3, including phase modulators and intensity modulators, are vulnerable to photorefractive effect caused by external light injection. By changing the power of external light, eavesdroppers can control the intensities of the prepared states, posing a potential threat to the security of QKD. We have experimentally demonstrated the influence of light injection on LiNbO3-based optical modulators and analyzed the security risks caused by the potential green light injection attack, along with the corresponding countermeasures.