| In today’s information society, communication technology isbecoming more and more important, and the demand for informationsecurity becomes higher. Classical cryptography is useful to protectinformation, whereas it faces challenges from the development ofcomputer technology and quantum computation, due to its hypothesis oncomputationally complexity. By contrast, quantum cryptography is built onthe basic principles of quantum mechanics, thus providinginformation-theoretic security.Quantum key distribution (QKD) is an important application ofquantum cryptography, which enables two legal parties，Alice and Bob，toshare a absolutely secure key, in spite of the existence of a eavesdropperEve，guaranteed by the uncertainty principle and quantum no-cloningprinciple. A QKD protocol includes four main steps，that is，quantumchannel transmission，data sifting，reconciliation and privacy amplification.The last two steps are generally together referred to as postprocessing andits performance greatly influences the key rate and secure communicationdistance of QKD.Continuous variable QKD has advantage of simpler equipment,higher achievable channel capacity and so on, thus has a better applicationprospect compared to discrete variable QKD. However, the realizationrequires more efficient continuous variable postprocessing algorithmswhich are much more complex.In this thesis, we focus on the research of postprocessing algorithm inthe continuous variable QKD, especially the reconciliation algorithm. We investigate details of several postprocessing algorithms,try to make someimprovements, and implement the algorithm using software. The mainwork is as follows.1.We deeply analyse and discuss the process of Slice reconciliation,including the partition of interval, design of estimating function, andcalculation of reconciliation efficiency. An improvement on intervalpartition is presented. After that, we apply inter-layer iteration to the Slicereconciliation, and design an effective way for the computation of initialprobability used in the decoding of LDPC codes. Also, we investigate thescheme of embedding Cascade algorithm in Slice reconciliation throughsimulation, and verify its performance.2.We study the application of LDPC codes in the multidimensionalreconciliation algorithm，analyse the noise model of equivalent channel，and design practical formula to calculate the posterior probability fordecoding of binary and non-binary LDPC codes. Through simulation, wedemonstrate that a performance gain can be achieved by using non-binarycodes.3.We design and implement a postprocessing software. This softwarecan realize the fuction of reconciliation and privacy amplification. Also,due to its good extensibility,future development of postprocessing softwarewith higher performance can be built on its framework. |
