Security-proof framework for two-way Gaussian quantum-key-distribution protocols

TL;DR

This paper develops a security proof framework for two-way Gaussian quantum key distribution protocols, reducing coherent attack security to collective attack security and identifying key intrusion parameters.

Contribution

It introduces a general security proof framework for two-way Gaussian QKD protocols, addressing the gap in security analysis for such protocols.

Findings

Coherent-attack security can be reduced to collective-attack security.

Two constraints provide bounds on eavesdropper's information gain.

Framework applied successfully to two specific protocols.

Abstract

Two-way Gaussian protocols have the potential to increase quantum key distribution (QKD) protocols' secret-key rates by orders of magnitudes~[Phys.~Rev.~A {\bf 94}, 012322 (2016)]. Security proofs for two-way protocols, however, are underdeveloped at present. In this paper, we establish a security proof framework for the general coherent attack on two-way Gaussian protocols in the asymptotic regime. We first prove that coherent-attack security can be reduced to collective-attack security for all two-way QKD protocols. Next, we identify two different constraints that each provide intrusion parameters which bound an eavesdropper's coherent-attack information gain for any two-way Gaussian QKD protocol. Finally, we apply our results to two such protocols.