# Reputation-Driven Dynamic Node Consensus and Reliability Sharding Model in IoT Blockchain
###### Abstract  
The Internet of Things that links the cyber and physical worlds brings revolutionary changes to society, however, its security and efficiency problems have not been solved. The Consortium Blockchain + IoT is considered to be an effective solution. The IoT blockchain network's demand for transaction processing speed is gradually increasing. The throughput problem of the blockchain needs to be solved urgently and the security problem of transaction processing that comes with it. To solve the above problems, this paper proposes a reputation-driven dynamic node security sharding consensus model (RDSCM) in the blockchain, which consists of two parts: a reputation-driven node to eliminate PBFT (RE-PBFT) and a reputation-driven node cross reconfiguration sharding scheme (NCRS). The RE-PBFT eliminates abnormal nodes in the consensus network and reduces the probability of abnormal nodes becoming master nodes. NCRS improves the blockchain throughput while ensuring sharding reliability. Finally, the experiment proves that RE-PBFT can identify abnormal nodes and remove them in a short time. NCRS can effectively guarantee the reliability of sharding, and the transaction processing efficiency has been greatly improved after sharding. blockchain; Internet of Things; reputation; node eliminate; sharding +
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which has been criticized for a long time, still exists. Bitcoin handles about 3-4 transactions per second, while Ethereum only handles 14 transactions per second [14]. Therefore, the IoT blockchain generally adopts the PBFT as the concordant protocol of the consortium blockchain. The consortium blockchain has the characteristics of openness, transparency, and decentralization, and its throughput is greatly improved compared with the public chain. Common consensus algorithms in the consortium blockchain include IBFT [15], PoA [16], PoET [17], PBFT [18], etc., as shown in Table 1. PoA has a large delay and cannot meet the needs of the Internet of Things, while PoET mainly runs in Intel's SGX security environment and cannot be used in the Internet of Things environment with a wide range of devices; the theory and performance of IBFT and PBFT are almost the same, so the more classical PBFT is generally used as the common consensus algorithm in the Internet of Things blockchain, and PBFT also has some problems. With the development of IoT blockchain, the number of users participating in the consensus has increased, and the consortium blockchain has also exposed its problems. First, with the increase of users participating in the consensus, the transaction processing speed decreases; secondly, the increase in users may lead to the increase of abnormal nodes. Finally, the characteristic of PBFT is that it tolerates malicious nodes without corresponding measures, which may cause a distributed system to crash. Solving these problems is the focus of this paper. To solve the above problems, this paper first proposes an evaluation scheme for quantifying node behavior. Based on the evaluation scheme, a reputation driven node elimination PBFT (RE-PBFT) is proposed to optimize PBFT consensus. Its advantages are as follows: (1) The master node is selected based on reputation. Only with high reputation can it become a master node and reduce the possibility that a malicious node becomes a master node and harm the consensus network; (2) The local outlier factor algorithm (LOF) is used to judge the abnormal nodes and remove them from the consensus network, to reduce the number of malicious nodes in the consensus network and make the total number of malicious nodes far away from the number of tolerated malicious nodes. In addition, a reputation-driven node cross reconstruction sharding scheme (NCRS) is proposed to ensure the reliability of sharding, and the concepts of ranking sharding and consensus sharding are proposed to improve the consensus speed after sharding.