Device calibration impacts security of quantum key distribution

TL;DR

This paper demonstrates how improper device calibration in quantum key distribution systems can create security vulnerabilities, and proposes a method to exploit this flaw along with a potential fix.

Contribution

It introduces a novel attack exploiting calibration routines in QKD systems and suggests a practical countermeasure to enhance security.

Findings

Calibration routines can be manipulated to create security loopholes.

An attack using faked states can break QKD security.

A proposed fix can mitigate the calibration-based attack.

Abstract

Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Moreover, an inappropriately implemented calibration routine can open a fatal security loophole. We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial QKD system by deceiving a channel length calibration routine. We then devise an optimal and realistic strategy using faked states to break the security of the cryptosystem. A fix for this loophole is also suggested.