Wide-spectrum security of quantum key distribution

TL;DR

This paper introduces a comprehensive method for evaluating the spectral security of quantum key distribution systems by characterizing optical component transmittance over a broad wavelength range.

Contribution

It presents a wide-spectrum security evaluation technique and a testbench for fiber-optic component characterization from 400 to 2300 nm, enhancing QKD system certification.

Findings

Testbench achieves up to 70 dB dynamic range in transmittance measurement.

Method enables full optical spectrum safety assessment for QKD systems.

Analysis of Trojan-horse and detector-backflash attacks demonstrates practical application.

Abstract

Implementations of quantum key distribution (QKD) need vulnerability assessment against loopholes in their optical scheme. Most of the optical attacks involve injecting or receiving extraneous light via the communication channel. An eavesdropper can choose her attack wavelengths arbitrarily within the quantum channel passband to maximise the attack performance, exploiting spectral transparency windows of system components. Here we propose a wide-spectrum security evaluation methodology to achieve full optical spectrum safety for QKD systems. This technique requires transmittance characterisation in a wide spectral band with a high sensitivity. We report a testbench that characterises insertion loss of fiber-optic components in a wide spectral range of 400 to 2300 nm and up to 70 dB dynamic range. To illustrate practical application of the proposed methodology, we give a full Trojan-horse attack analysis for some typical QKD system configurations and discuss briefly induced-photorefraction and detector-backflash attacks. Our methodology can be used for certification of QKD systems.