TP-PBFT: A Scalable PBFT Based on Threshold Proxy Signature for IoT-Blockchain Applications

Consensus protocol is one of the core technologies of Internet of Things (IoT)-blockchain applications, which is used to ensure the consistency of data between terminal devices that do not trust each other. Practical Byzantine fault tolerance (PBFT) is a typical consensus algorithm. Due to its advantages of low computational power and complexity, PBFT is deemed more suitable for IoT-blockchain applications. PBFT can tolerate 1/3 faulty nodes in a blockchain network, which can be malicious or unresponsive. In this work, if a node does not respond to messages from other nodes, it can be regarded as an offline node. Therefore, when more than a third of the nodes go offline, the blockchain network breaks down. However, in IoT applications, this situation is likely to occur and greatly limits the security and stability of IoT-blockchain networks. In order to solve the above problem, we propose a novel threshold proxy signature-based PBFT (TP-PBFT) consensus for IoT-blockchain applications. We construct a new threshold proxy signature scheme that enables the proxy signers to sign messages on behalf of the offline nodes. In addition, we design a "two-step clustering" method to construct a double-layer architecture that improves the scalability of PBFT. Meanwhile, a reputation mechanism is introduced to evaluate the quality of the nodes. The experimental results show that our TP-PBFT consensus protocol can reach consensus when the number of offline nodes more than 1/3.