Testing random-detector-efficiency countermeasure in a commercial system reveals a breakable unrealistic assumption

TL;DR

This paper evaluates the robustness of ID Quantique's random-detector-efficiency countermeasure in quantum key distribution, revealing it is vulnerable to modified blinding attacks due to unrealistic hardware assumptions.

Contribution

It provides the first third-party testing of this countermeasure, demonstrating its practical vulnerabilities against modified attacks despite theoretical security proofs.

Findings

Original countermeasure effective against initial attack

Vulnerable to modified blinding attack in practice

Hardware assumptions in security proof are unrealistic

Abstract

In the last decade, efforts have been made to reconcile theoretical security with realistic imperfect implementations of quantum key distribution (QKD). Implementable countermeasures are proposed to patch the discovered loopholes. However, certain countermeasures are not as robust as would be expected. In this paper, we present a concrete example of ID Quantique's random-detector-efficiency countermeasure against detector blinding attacks. As a third-party tester, we have found that the first industrial implementation of this countermeasure is effective against the original blinding attack, but not immune to a modified blinding attack. Then, we implement and test a later full version of this countermeasure containing a security proof [C. C. W. Lim et al., IEEE Journal of Selected Topics in Quantum Electronics, 21, 6601305 (2015)]. We find that it is still vulnerable against the modified blinding attack, because an assumption about hardware characteristics on which the proof relies fails in practice.