Robust countermeasure against detector control attack in practical quantum key distribution system

TL;DR

This paper introduces a simple, detector-agnostic countermeasure for quantum key distribution systems that effectively detects and defends against detector control attacks, including those without blinding light, through statistical analysis.

Contribution

It proposes a novel, practical countermeasure using a variable attenuator that is effective against various detector control attacks and applicable to existing QKD systems.

Findings

Countermeasure successfully detects attacks with blinding light.

Effective against concealed attacks without blinding light.

Supported by theoretical proof and experimental demonstration.

Abstract

In real-life implementations of quantum key distribution (QKD), the physical systems with unwanted imperfections would be exploited by an eavesdropper. Based on imperfections in the detectors, detector control attacks have been successfully launched on several QKD systems, and attracted widespread concerns. Here, we propose a robust countermeasure against these attacks just by introducing a variable attenuator in front of the detector. This countermeasure is not only effective against the attacks with blinding light, but also robust against the attacks without blinding light which are more concealed and threatening. Different from previous technical improvements, the single photon detector in our countermeasure model is treated as a blackbox, and the eavesdropper can be detected by statistics of the detection and error rates of the QKD system. Besides theoretical proof, the countermeasure is also supported by an experimental demonstration. Our countermeasure is general in sense that it is independent of the technical details of the detector, and can be easily applied to the existing QKD systems.