利用LDPC编译码构建无线密钥协商协议的研究

基于无线信道特征的密钥生成过程中，为了降低通信双方生成的密钥不一致率常采取的措施是密钥协商。通常的密钥协商过程是在BSC信道下进行密钥协商，但是协商的效率较低。为了提高密钥协商的效率，本文提出一种在等效信道下基于LDPC编译码的协议机制。在此协议机制中，无线信道下采用Mathur1]2]等人提出的Level-Crossing算法（LCA）提取密钥的过程构成了本协议中的等效信道，该机制对LCA提取后的密钥协商信息进行建模，推导了等效信道的最佳似然比，并据此采用LDPC码简单的加权比特翻转等译码算法3-5]来有效进行密钥协商。将等效信道下LDPC码加权比特译码算法用于协商过程的性能和BSC信道下协商后的性能进行仿真，在SNR大于6db的前提下，仿真结果表明:1）在相同低门限的条件下，和LCA算法生成的初始密钥相比较，利用LDPC码比特翻转译码等算法在等效信道下和在BSC信道下协商后的密钥不一致率比初始密钥不一致率降低1至2个数量级；2）在等效信道下利用简单加权比特翻转译码算法进行密钥协商后的密钥不一致率比BSC信道下协商后的密钥不一致率降低大约1个数量级。 

The Research of Using LDPC Encoding and Decoding to Structure Wireless Key Reconciliation Protocol

In the process of key generation based on wireless channel characteristics, in order to reduce the rate of key inconsistent, we usually reconcile key generated by legal both communication sides. The process of key reconciliation commonly take place in the BSC channel, but the negotiation efficiency is low. In order to improve the efficiency of key reconciliation, we propose a protocol mechanism based on LDPC encoding and decoding under a equivalent channel. In this protocol mechanism, the use of Level-Crossing algorithm (LCA) proposed by Mathur1]2] et al in wireless channel to establish initial key which could be regarded as equivalent channel in this protocol, The mechanism is modelling the negotiated information which are extracted through LCA, inferring the best channel likelihood ratio, and using simple weighted bit-flipping decoding algorithm3-5] to effectively reconcile key. Compared with reconciliation performance under BSC channel, we proposed the performance of protocol is better which can be proved by simulation test. Under the case of SNR>6db, Simulation shows: 1) under the condition of same low threshold, comparing with the key generated by LCA algorithm, using LDPC decoding algorithms further reconcile key under equivalent channel and BSC channel results in that the key inconsistent rate reduce 1 to 2 orders of magnitude. 2) the performance of making use of simple weighted bit-flipping decoding algorithms to reconcile key under equivalent channel is better than performance in the BSC channel, the key inconsistent rate reduce about 1 order of magnitude than the rate under BSC channel.