Source‐Replacement Model for Phase‐Matching Quantum Key Distribution

Abstract

Quantum key distribution has emerged as a promising solution for constructing secure communication networks, with its information‐theoretic security rooted in quantum mechanics. One of the recent quantum key distribution protocols, the phase‐matching protocol, can have a quadratic key‐rate improvement. Its security was initially established using an abstract method known as symmetry‐protected privacy. In this study, this security is reevaluated under the more intuitive source‐replacement model, arriving at the same conclusions as the original proof. This model provides a fresh perspective on the protocol's security. As an application of this approach, a beam‐splitting attack is introduced. Leveraging the source‐replacement model, a lower bound on the phase error rate under this attack is derived, further underscoring the robustness of our security analysis method.