Research On Some Key Issues Of Semi-device-independent Quantum Key Distribution Protocols

Quantum key distribution(QKD)allows remote legal communicating parties to share secret keys.Combining with ?One-Time Pad?,it can achieve unconditional secure communication in ideal condition.Practical QKD systems are realized by specific physical processes of ideal QKD protocols.It is difficult to detect all imperfections of devices for various security loopholes in practical QKD systems.Therefore,researchers want to break through by designing QKD protocols and present device-independent QKD protocols,which can break through the limitations of dependence on quantum devices in the security of QKD.Since DI-QKD imposes very demanding requirements on practical demonstrations.Alternative proposals between DI-QKD and conventional QKD have become one of hot research topics of QKD.Semi-device-independent(SDI)QKD protocol confines quantum state within finite dimensional Hilbert space.SDI-QKD with no need for preparation of entanglement states is easier for implementation with existing experimental technology.In this thesis,we have further researched on the security of SDI-QKD protocols against collective attacks.The main works are as follows:1.Security analysis of a SDI-QKD protocol with four states against collective attacks.The analytical security bound against collective attacks is one of difficult points in progresses of the security proof of SDI-QKD protocols.For the SDI-QKD protocol with four states,we establish the relation between the full average guessing probability and the dimension witness value.Based on the relation between the full average guessing probability and the Min-entropy,we present the relation between the dimension witness value and the Min-entropy,which characterized the amount of information of Eve.Based on Devetak-Winter bound,we present formulas the secure key rate against collective attacks for the SDI-QKD protocol with for states.By numerical simulation,we analyze the relationship among the secure key rate,the dimension witness value and the bit error rate.Our results show that the bit error rate has a greater impact on the secure key rate when the dimension witness value is small.2.Finite-key analysis for a SDI-QKD protocol.Photon pulses generated by practical QKD systems are always finite,so taking finite-length keys into account is one of key problems in the practical security of QKD protocols.By using the SDI-QKD model based on the Clauser-Horne-Shimony-Holt(CHSH)correlator,we design a practical SDI-QKD protocol with prepare-and-measure(PM)settings.We present concrete description of the SDI-QKD protocol with finite resources.Based on smooth entropies,we present the amount of information of Eve against collective attacks.We characterize statistics fluctuations of quantum bit error rates and CHSH correlator values based on the Serfling theorem and Hoeffding inequality,separately.Then,based on the composable security definition,we present finite-key analysis of the protocol.Based on the depolarizing quantum channel model,we compared secure key rates in SDI-QKD protocols and BB84 protocol by numerical simulation.Our results show that our protocol is the the best performance among existing SDI-QKD protocols.3.Security analysis of a SDI-QKD protocol with weak coherent state(WCS).At present,the technology,which realizes ideal single photon sources,is not mature,so the protocol with weak coherent state(WCS)is one of effective ways to enhance the practicality of SDI-QKD.Based on the mathematical model of WCS source,we present the relation between the dimension witness value of single photon portion of WCS source and the practical observed dimension witness value.Based on the decoy state method and the GLLP formula,we present the secure key rate of the SDI-QKD protocol with WCS.We numerically analyze the relation the secure key rates and secure transmission distances.