Evaluation of quantum key distribution systems against injection-locking attacks

TL;DR

This paper experimentally characterizes how injection-locking attacks can de-randomize the phase in practical quantum key distribution systems, highlighting the importance of isolation to ensure security.

Contribution

It introduces a source-agnostic experimental method to quantify phase de-randomization caused by injection locking in QKD systems.

Findings

Injection locking can significantly reduce phase randomness in QKD sources.

A heterodyne detection setup effectively measures phase de-randomization.

The method provides a lower bound on isolation needed to prevent injection-locking attacks.

Abstract

While ideal quantum key distribution (QKD) systems are well-understood, practical implementations face various vulnerabilities, such as side-channel attacks resulting from device imperfections. Current security proofs for decoy-state BB84 protocols either assume uniform phase randomization of Alice's signals, which is compromised by practical limitations and attacks like injection locking, or rely on a (partially) characterized phase distribution. This work presents an experimental method to characterize the phase de-randomization from injection locking using a heterodyne detection setup, providing a lower bound on the degree of isolation required to protect QKD transmitters against injection-locking attacks. The methods presented are source-agnostic and can be used to evaluate general QKD systems against injection-locking attacks.