Controlling passively-quenched single photon detectors by bright light

TL;DR

This paper demonstrates a method for an eavesdropper to control passively-quenched single photon detectors using bright light, enabling successful intercept-resend attacks on quantum key distribution systems.

Contribution

It introduces a bright-light regime attack strategy on passively-quenched detectors, showing practical feasibility through experimental models and simulations.

Findings

Detectors can be blinded by sub-nanowatt light levels.

Eavesdropper can selectively control detector clicks via polarization adjustments.

The attack is practically feasible based on experimental simulations.

Abstract

Single photon detectors based on passively-quenched avalanche photodiodes can be temporarily blinded by relatively bright light, of intensity less than a nanowatt. I describe a bright-light regime suitable for attacking a quantum key distribution system containing such detectors. In this regime, all single photon detectors in the receiver Bob are uniformly blinded by continuous illumination coming from the eavesdropper Eve. When Eve needs a certain detector in Bob to produce a click, she modifies polarization (or other parameter used to encode quantum states) of the light she sends to Bob such that the target detector stops receiving light while the other detector(s) continue to be illuminated. The target detector regains single photon sensitivity and, when Eve modifies the polarization again, produces a single click. Thus, Eve has full control of Bob and can do a successful intercept-resend attack. To check the feasibility of the attack, 3 different models of passively-quenched detectors have been tested. In the experiment, I have simulated the intensity diagrams the detectors would receive in a real quantum key distribution system under attack. Control parameters and side effects are considered. It appears that the attack could be practically possible.