Bit-flipping Decoding Algorithm And Its Application In Key Agreement

Since LDPC codes was rediscovered,it has become the research focus in the field of channel coding because of the excellent performance and low decoding complexity.There are two main kinds of decoding algorithms for LDPC codes: BF(Bit-Flipping)algorithm and BP(Belief-Propagation)algorithm.BF algorithm has lower complexity,but it's performance is poorer,so it can only be applied to the circumstance where lower complexity is preferred;BP algorithm's performance is very good,but its complexity is too high.In order to achieve a trade-off between performance and complexity,many improved decoding algorithms were put forward by scholars.Due to the excellent performance of LDPC codes in general,LDPC decoding algorithm can be integrated into key negotiation process.Because the keys extracted in wireless channel is inconsistent,two key sequences need negotiate each other in order to reduce inconsistent rate.For the negotiayion,it requires two legitimate uses to exchange information,so the interactive information will be hacked and it's unsafe.The mechanism that LDPC decoding algorithms were integrated into key negotiation process doesn't need interactive information in open channel,so the key will not be leaked.The security of key sequences will be improved.If the key sequences are negotiated by mechanism include LDPC decoding algorithm,the inconsistent key rate will be reduced significantly.By focusing on above problems,contributions can be summarized as follows:(1)The hard decision decoding algorithm of LDPC codes including BF algorithm,WBF algorithm,IMWBF algorithm.A novel hard decision decoding algorithm--SNWBF decoding algorithm is proposed in this paper.Compared with WBF algorithms,the SNWBF decoding algorithm considers variable node itself;Compared with IMWBF algorithm,the SNWBF algorithm doesn't need more storage space.It compromises performance and complexity of LDPC code in a way.(2)Because the essence of key negotiation is correcting error codes,so LDPC code belongs to error correcting code.The mechanism that LDPC decoding algorithms were integrated into key negotiation process of wireless channel is proposed in the paper.Usually,only bit sequences from both sides were used in key negotiation,and the channel information doesn't be used.In this paper,we propose a new framework of equivalent channel model,and the protocol mechanism under an equivalent channel based on LDPC decoding algorithm is proposed.For key negotiation,we adopt Mathur's the Level-Crossing algorithm(LCA)to extract the key form the equivalent channel in the key negotiation,after deducing the best of equivalent channel likelihood rate,and adopt LDPC decoding algorithms such as simple weighted bits flip decoding algorithm to effectively negotiate keys.Simulations show that it works better than the previous approaches.