Research On And Implementation Of Quantum Key Distribution System With An Untrusted Source

Quantum information science is a cross-field subject of quantum physics and classical information science. Due to quantum superposition and quantum entanglement properties, it has a unique charm over classical information science. The unconditional security of Quantum Key Distribution(QKD) is guaranteed by the laws of quantum mechanics, which makes the security of key distribution fundamentally solved. And at present, QKD is the most applicable subject in the quantum information science. However, unconditional security is far different from absolute security. The ideal QKD protocol requires the use of the ideal single-photon source and ideal single-photon detector, which is impossible with the current state of technology. These imperfections can be maliciously exploited by an eavesdropper, making the QKD system vulnerable to various attacks, such as the photonnumbers-splitting attack(PNS attack) and side-channel attack. The decoy-state method to overcome the PNS attack makes it possible to use coherent laser source instead of the ideal single-photon source in practical QKD system. Since Measurement-Device-Independent quantum key distribution(MDI-QKD) could remove all detector side-channel attack, eavesdroppers will shift their focus from hacking the detectors to hacking the sources, which are not automatically protected in MDI-QKD. In the bidirectional QKD system, both phase and polarization drifts could be compensated for, resulting in a very stable and relatively low quantum bit error rate(QBER). However, in this QKD system, the strong classical pulses which Bob sends to Alice could be manipulated or even replaced by an eavesdropper with her own sophisticatedly prepared pulses. in other words, the source is fully controlled by eavesdroppers, making it unknown and untrusted. In this thesis, we focus on the research and implementation of quantum key distribution system with an untrusted source.Firstly, the basic concepts, present development situations and loopholes in the practical QKD systems are introduced briefly. Then the laws of quantum mechanics used to guarantee the unconditional security of QKD and the widely used protocols of QKD are introduced in detail. Also we discuss the analysis method of the decoy-state strategy in detail.Secondly, the security loopholes of the source in the practical QKD system are summarized and the corresponding methods to remove these loopholes are given in this article. A new MDI-QKD scheme with an untrusted source based on the polarization encoding strategy combining with the decoy-state strategy is also proposed, and followed by the protocol of this scheme. The untrusted source and the expensive detectors, which will be shared by both Alice and Bob, should be provided by the untrusted server. So a large amount of the experimental expense will be saved. Then a complete proof of the unconditional security is derived with the combination of decoy-state strategy analysis method and passive monitoring strategy, and also the secure key rate of MDI-QKD with an untrusted source is given. Followed by, a simulation was accomplished, and the simulation results show that MDI-QKD with an untrusted source provides a secure key generation rate that is close to the rate of MDI-QKD with a trusted source.Thirdly, a verification platform for the proposed MDI-QKD scheme is set up, and also we designed a control and data acquisition system by FPGA. We use the external synchronizing signal to trigger this work. And we send the coded data to the PC through a serial port. Now the control and data acquisition system is successfully used in the verification platform, and it will help to improve the efficiency of QKD.Finally, a summary and prospection is given at the end of this thesis. The proposed polarization encoding MDI-QKD scheme in this thesis only requires the server in the network possess the expensive laser source and detectors while Alice and Bob only need their encoding devices, that is, a star-type MDI quantum access network could be readily realized on the basis of our proposal. This will help to promote the development of QKD network towards to the direction of practical application.