Meanwhile, the sensors and edge devices in the IoT network may become the breaking point of malicious attackers due to the following reasons of lacking compliance on manufacturers and the complicated upgrade management [9]. Many IoT devices come out with undiscovered vulnerabilities in the hardware and software. For example, a group of hackers discovered one security vulnerability that can be used to perform a man-in-the-middle attack and gain the user's Gmail login credential [10]. Since there is no standard for the IoT connection module and interface, these security issues can not be upgraded and fixed easily, especially on the hardware side. Blockchain can help mitigate the security and scalability concerns associated with IoT in the way of security and scalability. The transformation from centralization to decentralization brought by the integration of blockchain avoids the risk of single-point failure and alleviates the pressure of communication over the entire network, such that the scalability is improved. At the same time, the maintenance of the network does not rely on the center server; therefore, the influence of the targeted DDoS attack can be reduced. The key idea of integrating IoT with blockchain is simple, but the implementation raises many challenges, and the most serious one is the choice of consensus protocol since consensus protocol forms the backbone of the blockchain network and affects efficiency and security. As we mentioned above, PoW is the most well-known consensus protocol, and it has been shown that it is an effective approach for the operation of the cryptocurrency system. However, it is not suitable for the IoT network due to the high energy consumption. PoET has significantly lower energy consumption, but reaching a consensus relies on the specific hardware platform, which is not practical for the large-scale deployment in the IoT environment. Proof of Capacity (PoC) is also similar to PoW, but the complex computation is replaced by the capacity of storage. It is well known that IoT devices are constrained by their small storage capacity and slow storage speed, which makes PoC not a viable choice. Other consensus protocols, such as the variants of PoS and Byzantine Agreement Methods, have higher efficiency and lower energy consumption than PoW, but few of them focus on the privacy of communication within the blockchain network. In most consensus protocols, the built blockchain network provides transparency by allowing all the authorized participants to review the content of the transaction and track the past blocks. This can help track the malicious actions and source but may leak sensitive information in some special application scenarios. Most of the current existing consensus protocols have some common shortcomings, such as low efficiency, centralization trend, high energy consumption, and privacy issues. The problems of low efficiency and high energy consumption make them impractical for the application of blockchain networks in the IoT environment. These issues motivate us to propose a privacy-preserving and efficient consensus protocol, which enables the blockchain network to be deployed in resource-constrained IoT networks. In this work, we present a consensus protocol that provides fairness during the election of nodes to pack the new block and preserves privacy during information transmission while maintaining efficiency. Our contributions can be summarized as follows:  
1. To achieve the fairness of the election, we propose a random algorithm to randomly choose several nodes as the packers based on all of the nodes' given parameters. 2. The feature of privacy-preserving is implemented with verifiable secret sharing, in which the information is split and then encrypted so as to protect the sensitive information during transmission. 3. We propose one method to keep the efficiency of the election when the number of nodes in the blockchain network is very large. 4. Evaluation results and analysis show the efficiency and security of our scheme.