Practical security bounds against the Trojan-horse attack in quantum key distribution

TL;DR

This paper quantifies security bounds against Trojan-horse attacks in quantum key distribution by relating optical component specifications to information leakage, supported by experimental characterization.

Contribution

It transforms the Trojan-horse attack into an information leakage problem and provides quantitative security bounds based on optical component parameters.

Findings

Established quantitative bounds linking optical component specs to security

Experimental measurements of reflectivity and transmission relevant to security

Demonstrated how to prevent Trojan-horse attacks using component specifications

Abstract

In the quantum version of a Trojan-horse attack, photons are injected into the optical modules of a quantum key distribution system in an attempt to read information direct from the encoding devices. To stop the Trojan photons, the use of passive optical components has been suggested. However, to date, there is no quantitative bound that specifies such components in relation to the security of the system. Here, we turn the Trojan-horse attack into an information leakage problem. This allows us quantify the system security and relate it to the specification of the optical elements. The analysis is supported by the experimental characterization, within the operation regime, of reflectivity and transmission of the optical components most relevant to security.