Simple proof that Gaussian attacks are optimal among collective attacks againstcontinuous-variable quantum key distribution with a Gaussian modulation

摘要

In this article, we give a simple proof of the fact that the optimal collective attacks against continuous-variable quantum key distribution with a Gaussian modulation are Gaussian attacks. Our proof, which makes use of symmetry properties of the protocol in phase space, is particularly relevant for the finite-key analysis of the protocol and therefore for practical applications.