Security boundaries of an optical power limiter for protecting quantum key distribution systems

TL;DR

This paper investigates the security boundaries of an optical power limiter used in quantum key distribution systems by testing its response to various light-injection attacks, providing guidelines for its effective deployment.

Contribution

It offers a comprehensive testing methodology for the security boundary of an optical power limiter in QKD, applicable to other power-limiting components.

Findings

Identified the security boundary of the OPL under different attack conditions.

Demonstrated the effectiveness of the OPL against specific light-injection attacks.

Provided a testing framework for evaluating power-limitation hardware in quantum cryptography.

Abstract

Unauthorized light injection has always been a vital threat to the practical security of a quantum key distribution (QKD) system. An optical power limiter (OPL) based on the thermo-optical defocusing effect has been proposed and implemented, limiting the injected hacking light. As a hardware countermeasure, the performance of the OPL under various light-injection attacks shall be tested to clarify the security boundary before being widely deployed. To investigate the OPL's security boundary in quantum cryptography, we comprehensively test and analyse the behavior of OPL under continuous-wave (c.w.) light-injection attacks and pulse illumination attacks with pulses' repetition rate at $0.5$-$\hertz$, $40$-$\mega\hertz$, and $1$-$\giga\hertz$. The testing results illuminate the security boundary of the OPL, which allows one to properly employ the OPL in the use cases. The methodology of testing and analysis proposed here is applicable to other power-limitation components in a QKD system.