Study On Error Control Coding In Quantum Key Distribution Systems

With the rapid spread of the Internet,the communication security has been a very big problem,which draws much attention,while it brings us a lot of convenience.Meanwhile,as the speedy development of computer science,the classic cryptography is being challenged.The quantum cryptography,proved to be absolutely safe in theory,has attracted extensive attention since its presentation.In the new era,it's more and more popular and becomes a research hotspot.As a typical application of the quantum physics in cryptography,the quantum key distribution(QKD)system has a very important value both in military and civil use for its theoretical security and lays a very solid foundation of the quantum communication development.This thesis focuses on the info reconciliation of the secret key distillation in the QKD system.The main contents are as follows:The quantum key distribution system with its post-processing is introduced and the whole process of the key distribution is described detailedly.The features of the QKD system are given and are compared with the classic cryptography's.The challenges and future aims of the QKD system development are also given.Besides,the technical indexes and requirements of the system are presented.Especially,the info reconciliation problem is detailedly analyzed and transformed to a source coding problem with side information.From the point of coding,the performance limit is given based on the Slepian-Wolf theorem.After analyzing some classic info reconciliation protocols,such as BBBSS and Casecade,for protocols using low-density parity-check(LDPC)codes,a new simple construction method of LDPC codes with computer search is presented.Meanwhile,a detailed description of an LDPC code including its encoding and decoding algorithms is made.The process of the error correction using an LDPC code in the QKD system is also introduced.With the new construction method,several LDPC codes are constructed and applied to the info reconciliation of the QKD system to evaluate their performance.Furthermore,a simple analysis and comparison of these protocols are made.Based on the classical protocols and considering the requirements of QKD system,a new info reconciliation scheme using multi-dimension Turbo product codes(MD-TPC)is proposed.The new scheme uses the forward error correction method and reduces the inter-actions between the sender and the receiver,thus increasing the throughput and reducing the delay of the system.The new scheme adopts a long code constructed from short component codes and is very flexible.Furthermore,the encoding is very simple and the best iterative soft-output decoding algorithm is applied in the decoding.The description of the new scheme's whole process including the encoding and decoding algorithms is precisely made.The simulation results show that the new error correction method can obtain excellent performance.