Security analysis of continuous-variable quantum key distribution using m-PSK classical modulation schemes

Abstract

Quantum key distribution (QKD), one of the most mature applications of quantum information theory, allows two authenticated users, Alice and Bob to share a sequence of random numbers for classical symmetric encryption over an insecure channel [1]. QKD can be categorized into two classes of protocols, namely continuous variable (CV) and discrete variable (DV) protocols, based on the dimension of the Hilbert space that the information is encoded onto. Unlike DVQKD which has a rather complete security analysis for different protocols against coherent attacks [1], only the Gaussian modulated CVQKD protocol has been proved theoretically secure based on Gaussian optimality [2]. However, CVQKD using discrete modulation (DM) has many intrinsic advantages in practical applications, e.g., more compatible with classical coherent communication technologies, potentially higher key rate and easier post-processing and error correction. However, owing to the difficulty of security analysis for CV quantum states, the development of CVQKD using efficient classical digital communication schemes has been severely delayed.