Best-practice criteria for practical security of self-differencing avalanche photodiode detectors in quantum key distribution

TL;DR

This paper investigates the security of fast-gated avalanche photodiodes in quantum key distribution, revealing how negative feedback prevents blinding attacks and proposing best practices for secure detector design.

Contribution

It introduces a set of best-practice criteria for designing and operating APD detectors to enhance their security against external attacks in QKD systems.

Findings

Negative feedback reduces detector blinding risk.

Photocurrent safeguards detector from external control.

Proposed criteria improve practical security of APDs.

Abstract

Fast gated avalanche photodiodes (APDs) are the most commonly used single photon detectors for high bit rate quantum key distribution (QKD). Their robustness against external attacks is crucial to the overall security of a QKD system or even an entire QKD network. Here, we investigate the behavior of a gigahertz-gated, self-differencing InGaAs APD under strong illumination, a tactic Eve often uses to bring detectors under her control. Our experiment and modelling reveal that the negative feedback by the photocurrent safeguards the detector from being blinded through reducing its avalanche probability and/or strengthening the capacitive response. Based on this finding, we propose a set of best-practice criteria for designing and operating fast-gated APD detectors to ensure their practical security in QKD.