Differential Quantum Cryptography Communication System Solutions And Stability Study

Since ancient times, secret communications play a unique role in militaryand diplomacy. Cryptology is one of the technical tools for secretcommunications, where secrecy is based on the secrecy of keys. Quantumcryptography is a combination of quantum mechanics and cryptology. Thedifferential-phase-shift quantum key distribution scheme is one of the mostpromising schemes of quantum cryptography, which is the main content ofthis dissertation.In Chapter 1, the related principles and concepts of the quantum securitysystem are mainly introduced, including: the development and basic conceptsof cryptology.In Chapter 2, the related principles of the quantum key distribution aremainly introduced, including: the quantum key generation course and thesingle photon quantum key distribution schemes. We give the instruction ofBB84 scheme, B92 scheme and differential phase shift quantum keydistribution (DPS-QKD) scheme. The evolement of the DPS-QKD scheme isdiscussed in detail.In Chapter 3, the factors which influence the stability of the system arepresented, as well as the interference instruments which can enhance thestability of the system.In Chapter 4, a novel phase modulated quantum key distribution schemewith high security, which is combined DPS-QKD with BB84 scheme andcalled biprotocol of quantum cryptography, is proposed in this part. Thisscheme has several advantages: firstly, as we know, only {0,p} is used tomodulate the phase in DPS-QKD scheme, the degree of the freedom is one, soit is not security against intercept-and-resend attacks for this scheme. But inthe biprotocol of quantum cryptography, we use {0, p} and {p/2, 3p/2}together to modulate the phase of the pulses which makes the degree of thefreedom becomes two and thus enhance the security of the scheme. Secondly,in order to enhance the stability of the whole system, we use two MZinterferometers with Faraday-mirrors-based Michelson interferometers whichis used to compensate for birefringence and polarization-dependent losses inthe fiber in Bob' site. Lastly, we evaluate the security in two different basesseparately to enhance the security of the system. We propose biprotocol ofquantum cryptography for two pulses and unsymmetrical biprotocol of quantum cryptography for multiple pulses.In biprotocol of quantum cryptography for two pulses, we use a fiber MZinterferemeter to generate the two pulse signals to encode information.DPS-QKD scheme which is used for most of the time and BB84 scheme areused together to enhance the security.In unsymmetrical biprotocol of quantum cryptography for multiplepulses, we use a coherent light source to generate pulses, select the phase tomodulate the pulses from {0, p} with the probability ofη(ηâ†'1) and selectthe phase to modulate the pulses from {p/2, 3p/2} with the probability of (1—η). By this way, the key generation rate and the security of the system areboth enhanced a lot.The biprotocol of quantum cryptography is the innovation of thisdissertation and experiments has been down to domenstrate the feasibility ofit.