| Quantum cryptography is a new rapid improvement technology of encryption.It mainly contains quantum physics,electrical information,and the cryptography.Quan-tum cryptography has incomparable advantages of classical cryptography in the aspect of information security.In cryptography theory,if the encryption key is random every time which is called one-time-pad,information transmission will be secure,however,one-time-pad needs very large random keys,and it is difficult for classical cryptography to distribute so large random keys.Based on the principle of non-clone theorem and measuring collapse theorem in quantum mechanics,Quantum key distribution(QKD)provides a one-time-pad solution which promise a unconditional security of transmis-sion.With the rapid improvement of QKD,practical engineering application system has been already implemented in cryptography field.The key generated by QKD system is "unconditional secure",which is of great value for both military and civilian use.Since the first QKD demonstration system in 1989 which was designed by Bennett etc,more and more QKD systems were designed.By now,QKD network based on fiber has appeared up.Satellite to ground QKD was implemented in China in 2016.The developing target of QKD in future are long distance and high-speed final key rate.Quantum Science Experimental Satellite(QSES)validated the QKD between satellite to ground with the final key rate at Kbps at the distance of 1000km.To achieve higher final key rates,satellite to ground QKD system requires a higher photon-emitting frequency and corresponding quantum post processing(QPP)technology.Because of the long distance between satellite to ground(1000km-36000km),long time delay is about several milliseconds,QPP is the most dragging unit for entire QKD because of the big latency and high data throughput.QPP is designed to remove the discrepancy and improve the security level of the final key.QPP mainly contains the following steps:(1)Basis sifting;(2)Error reconciliation;(3)Privacy amplification.This thesis deals with the simulation of high-speed satellite to ground QKD,and technology aimed to speed up the QPP to satisfy the needs of high-speed satellite to ground QKD in the future.This thesis implement a high speed satellite to ground QKD demonstration system.Considering the demand of a small-size system,convenience of the QKD device,the whole system is designed in one PCB which contains a Field Programable Gate Array(FPGA)and a high speed POWERPC,Alice and Bob share the same hardware(PCB)system.In this thesis,we concentrate the QKD data flow procedure on FPGA and command control on POWERPC.This thesis researches on four kinds of high-speed technology of QKD:simulation system for high-speed QKD based on FPGA,error correction for QKD based on FPGA,privacy amplification on FPGA and high speed data link between FPGA,POWERPC and PC.As for the simulation part,this thesis implemented the simulation module to simu-late photon-emitting,APD-detection,and the quantum channel of free space.We design a four-stage pipeline DDR structure to emit the 4GHz."photons" and detect the "pho-tons" at the frequency of 4GHz.Because the long distance between satellite to ground,the DDR can store as much as 1Gb data,then a qubit sample algorithm is picked up to simulate the property of quantum channel based on free space.The qubit sample algo-rithm in this thesis simulates the attenuation of the free space,the transmission delay which caused by the long distance,and the atmospheric turbulence.We can set up the simulation QKD procedure by this simulation module and simulate different conditions QKD.As for error reconciliation,this thesis design and implement two different error corrections based on low density parity check codes(LDPC):Bit flipping(BF)decod-ing and normalized min-sum algorithm(NMSA)decoding.We adopt a irregular quasi cyclical LDPC(IR-QC-LDPC)matrix as the check matrix,the IR-QC-LDPC can reduce the store space and save a lot of store space.Both BF and NMSA adopt a part-parallel decoding style.Both algorithm contain only add and simple multiply algorithm and can be implemented in hardware.LDPC is very suitable for parallel process,FPGA is adopted to implement the algorithm.As for privacy amplification(PA),we design and implement a FFT algorithm based on Toeplitz matrix.Unconditional secure is the key feature of QKD,we can reduce the probability of the final keys stole by a third party through PA.In this thesis,three FFT IP cores of FPGA are adopted to implement the PA,pipeline is used to reduce the waiting time and improve the throughput.As for high speed data link,this thesis implement the high data link channel among FPGA,POWERPC and PC.We need PC to analyze the final key error rate,send com-mand to control QKD and acquire the QKD work sate.FPGA transmit the sift keys,bit error rate(BER)by frame every seconds.PCIe is used between FPGA and POWERPC,TCP/IP is used between POWERPC and PC.As for PCIe,we design the direct memory access(DMA)in FPGA to send data to POWERPC,a PCIe driver based on VxWorks was designed to communicate with FPGA.TCP/IP protocol is implemented between POWERPC and PC,a client program is designed in PC with TCP/IP protocol.In this thesis,a high-speed satellite-to-ground QKD demonstration system is set up.We test the performance under different conditions.We validate the feasibility of the QKD procedure control and QPP.The innovation of the thesis is listed as following:(1)To simulate the high-speed satellite-to-ground QKD in future,a high-speed four-stage-pipeline DDR structure is designed.The photons-emitting frequency and APD detecting frequency is as high as 4GHz,this module also simulate the prop-erty of the long distance quantum channel based on free space.(2)LDPC-code based on IR-QC-LDPC matrix,partly parallel style is used to improve decoding throughput.NMSA algorithm are implemented individually.NMSA al-gorithm can reduce complexity and save a lot of memory space.(3)Privacy amplification uses FFT based on Toeplitz matrix.The FFT algorithm can reduce complexity and save a lot of memory space. |
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