Research On The Application Of Modified Coherent State Sources And The Technology Of Blind Reconciliation In Quantum Key Distribution Systems

Cryptography is crucial in the modern information society.With the development of quantum computers,the security of traditional cryptographic systems is under great threat.However,quantum key distribution(QKD)has attracted widespread attention from researchers as it can provide two remote legitimate users,Alice and Bob,with unconditionally secret keys even in the presence of an eavesdropper,Eve.The QKD process comprises two stages: quantum signal transmission and classical post-processing.Quantum signal transmission involves preparation,transmission,and measurement of quantum states to generate the raw keys,while classical post-processing comprises basis sifting,error estimation,key reconciliation,error correction,and privacy amplification based on an authenticated classical channel,so as to obtain the final secret keys.This thesis focuses primarily on practical technologies involving these two stages and outlines the specific work conducted as follows:(1)In order to enhance the generation rate of the raw keys,we study the reference-frameindependent QKD(RFI-QKD)protocol,which allows authorized communication parties to securely transmit keys with slowly drifted and unknown reference frames.In practical RFI-QKD systems,weak coherent state(WCS)sources are widely used as substitutes for ideal single photon sources.However,WCS sources are vulnerable to photon number splitting attacks due to inevitable multiphoton events.Fortunately,modified coherent state(MCS)sources can remove multi-photon events and optimize the photon-number distribution.Therefore,we propose a decoy-state RFI-QKD protocol based on MCS sources and evaluate its practical performance with statistical fluctuations.The simulation results demonstrate that MCS sources can improve the secret key rate and transmission distance in the decoy-state RFI-QKD protocol compared to WCS sources.(2)Taking into account the fact that quantum channel conditions are not entirely independent,we propose a blind reconciliation continuous transmission scheme based on polar codes to enhance the rate of producing the final secret keys.Simulation results demonstrate that the blind reconciliation continuous transmission scheme based on polar codes performs better in balancing inefficiency and communication interaction rounds than the blind reconciliation scheme.Moreover,under high quantum bit error rates,it offers quick adaptability to channel changes,significantly reduces communication interaction delays,ensuring error correction performance and enhancing transmission efficiency,which results in an improved rate of generating the final secret keys.