Preparing a commercial quantum key distribution system for certification against implementation loopholes

A commercial quantum key distribution (QKD) system needs to be formally certified to enable its wide deployment. The certification should include the system's robustness against known implementation loopholes and attacks that exploit them. Here we ready a fiber-optic QKD system for this procedure. The system has a prepare-and-measure scheme with decoy-state BB84 protocol, polarisation encoding, qubit source rate of 312.5 MHz, and is manufactured by QRate in Russia. We detail its hardware and post-processing. We analyse the hardware for any possible implementation loopholes and discuss countermeasures. We then amend the system design to address the highest-risk loopholes identified. We also work out technical requirements on the certification lab and outline its possible structure.Comment: 33 pages, 11 figures, 2 table

Protecting fiber-optic quantum key distribution sources against light-injection attacks

A well-protected and characterised source in a quantum key distribution system is needed for its security. Unfortunately, the source is vulnerable to light-injection attacks, such as Trojan-horse, laser-seeding, and laser-damage attacks, in which an eavesdropper actively injects bright light to hack the source unit. The hacking laser could be a high-power one that can modify properties of components via the laser-damage attack and also further help the Trojan-horse and other light-injection attacks. Here we propose a countermeasure against the light-injection attacks, consisting of an additional sacrificial component placed at the exit of the source. This component should either withstand high-power incoming light while attenuating it to a safe level that cannot modify the rest of the source, or get destroyed into a permanent high-attenuation state that breaks up the line. We demonstrate experimentally that off-the-shelf fiber-optic isolators and circulators have these desired properties, at least under attack by a continuous-wave high-power laser.Comment: Abstract, Fig.5 and discussion section modified. Various minor corrections, including clarification and explanation about the experimental setup stability and its graphical representation; testing procedure; configuration of QKD systems with circulators; heating of isolators; testing results of circulators' port couples. New references added in the bibliography. 13 pages, 6 figures, 2 table