Randomized ancillary qubit overcomes detector-control and intercept-resend hacking of quantum key distribution

TL;DR

This paper introduces a randomized ancillary qubit scheme in quantum key distribution that effectively detects and prevents detector-control and intercept-resend hacking attacks, enhancing security with practical implementation.

Contribution

A novel polarization randomizer method in QKD that detects and thwarts specific hacking strategies, demonstrated both theoretically and experimentally.

Findings

The scheme triggers alerts against faked-state attacks.

It is effective with commercial off-the-shelf detectors.

The method enhances practical security of QKD implementations.

Abstract

Practical implementations of quantum key distribution (QKD) have been shown to be subject to various detector side-channel attacks that compromise the promised unconditional security. Most notable is a general class of attacks adopting the use of faked-state photons as in the detector-control and, more broadly, the intercept-resend attacks. In this paper, we present a simple scheme to overcome such class of attacks: A legitimate user, Bob, uses a polarization randomizer at his gateway to distort an ancillary polarization of a phase-encoded photon in a bidirectional QKD configuration. Passing through the randomizer once on the way to his partner, Alice, and again in the opposite direction, the polarization qubit of the genuine photon is immune to randomization. However, the polarization state of a photon from an intruder, Eve, to Bob is randomized and hence directed to a detector in a different path, whereupon it triggers an alert. We demonstrate theoretically and experimentally that, using commercial off-the-shelf detectors, it can be made impossible for Eve to avoid triggering the alert, no matter what faked-state of light she uses.