Safeguarding Quantum Key Distribution through Detection Randomization

TL;DR

This paper introduces a practical scheme combining passive and active detection randomization techniques to protect Quantum Key Distribution systems from common hacking attacks targeting single-photon detectors, demonstrated through experimental validation.

Contribution

It presents a novel, implementable countermeasure that passively and actively randomizes detection modes to prevent eavesdropper exploitation without modifying device internals.

Findings

Successfully demonstrated passive spatial mode randomization.

Implemented detector-scrambling to mitigate efficiency mismatch attacks.

Proved the approach's effectiveness against main quantum hacking strategies.

Abstract

We propose and experimentally demonstrate a scheme to render the detection apparatus of a Quantum Key Distribution system immune to the main classes of hacking attacks in which the eavesdropper explores the back-door opened by the single-photon detectors. The countermeasure is based on the creation of modes that are not deterministically accessible to the eavesdropper. We experimentally show that the use of beamsplitters and extra single-photon detectors at the receiver station passively creates randomized spatial modes that erase any knowledge the eavesdropper might have gained when using bright-light faked states. Additionally, we experimentally show a detector-scrambling approach where the random selection of the detector used for each measurement - equivalent to an active spatial mode randomization - hashes out the side-channel open by the detection efficiency mismatch-based attacks. The proposed combined countermeasure represents a practical and readily implementable solution against the main classes of quantum hacking attacks aimed on the single-photon detector so far, without intervening on the inner working of the devices.