Research On Free Space Quantum Cryptography Protocol In Terahertz Band

Ensuring information security is one of the primary concerns in today’s information age.With the rapid development of the Internet and computers,especially the emergence of new technologies such as quantum computing and distributed large-scale computing,classical cryptography based on mathematical computational complexity is constantly under impact.More than three decades ago,quantum cryptography was emerged to provide a new way for secure communication.Unlike classical cryptography,quantum cryptography can theoretically ensure unconditional security based on the basic principles of quantum mechanics.Quantum key distribution(QKD),the core of quantum cryptography,allows two or more legitimate communication parties at a distance to distribute secret keys with unconditional security in an insecure channel controlled by a malicious eavesdropper.This natural advantage is unmatched by classical cryptography.Most existing QKD systems use photons to carry messages and transmit them over optical fibers or free-space channels.However,with the rapid development of wireless communication,the problems of information security and spectrum resource scarcity are becoming more and more serious.Terahertz(THz)communication technology is considered to be one of the effective ways to realize the next generation of high-speed data transmission due to its extremely high bandwidth availability,especially for short-range high-speed wireless communication and satellite communication.It is significant to explore the feasibility of THz-QKD by organically integrating THz communication technology with QKD systems.This paper focuses on the system composition and protocol design of THz-QKD and investigates how to improve the secret key rate of THz-QKD and how to extend the point-to-point two-party THz-QKD protocol to a multi-party secret sharing protocol.The main innovative results achieved are as follows:1.Design and analysis of THz continuous-variable quantum key distribution scheme based on multicarrier multiplexing(MCM).MCM technology is one of the key technologies to solve the problem of high spectral efficiency and high transmission rate of the future wireless communication system.Its basic principle is to decompose the high-speed data sequence into several low-speed sequences and modulate them on subcarriers to realize the parallel transmission of keys in multiple channels,and then improve the key rate of the QKD system.Based on the MCM technology,this paper proposes a continuous-variable QKD scheme in THz band,introduces the system composition and workflow of the scheme,and analyzes the security of the scheme against Gaussian collective attacks and its performance under the indoor environment and in inter-satellite links.The results show that this scheme can greatly improve the secret key rate of the system,and we also theoretically verify the feasibility of the scheme in inter-satellite links.2.Design and analysis of quantum key distribution scheme based on quantum illumination in THz band.The original quantum key distribution scheme based on quantum illumination,also known as FL-QKD,is a new type of QKD protocol,which is theoretically capable of achieving a secret key rate of 2 Gbps in a 50 km fiber channel.This paper proposes a THz-FL-QKD scheme,introduces the system composition and workflow of the scheme,and analyzes the security of the scheme against individual and collective attacks and its performance in inter-satellite links.The results show that this scheme can theoretically achieve a secret key rate of 50 Mbps in a 200 km inter-satellite link,which also verifies its feasibility.3.Design and analysis of continuous-variable quantum key distribution scheme based on composable security in THz band.In the QKD system,based on the assumption of different capabilities of the eavesdropper,the loss and noise of the detector at the receiver can be classified into three possible trust levels according to the actual communication scenario:(1)Trusted-Loss and Trusted-Noise detector;(2)Trusted-Noise detector;(3)Untrusted-Loss and Untrusted-Noise detector.Based on these three different trust levels,this paper analyzes the composable security of continuous-variable QKD against Gaussian collective attacks in THz band and its performance in inter-satellite links.The results show how the scheme significantly improves the key rate and tolerates higher losses at different trust levels.This paper also verifies theoretically that this scheme is feasible in inter-satellite links even at the worst trust level.4.Design and analysis of continuous-variable quantum secret sharing scheme based on THz sources.Since the standard point-to-point two-party QKD can hardly meet the demand of multi-party secret key sharing,this paper proposes a(n,n)threshold continuous-variable sequential quantum secret sharing scheme based on THz source and continuous-variable QKD system,introduces the system composition and workflow of the scheme,and analyzes the security of the scheme against Gaussian collective attacks and its performance in intersatellite links.The results show that this scheme is theoretically feasible for achieving multiparty secret key sharing in inter-satellite links.