A Hybrid Double-layer BFT Consensus Protocol for Large-Scale IoT Blockchain

IoT-blockchain applications are becoming more popular in recent years. Proof-of-Work (PoW) algorithm is not suitable for IoT blockchains due to limited power and computing capability of IoT devices. Practical Byzantine Fault Tolerance (PBFT) protocol is a better choice. However, because of the frequent inter-node connections, the PBFT algorithm has a poor node scalability. In this paper, we propose a hybrid double-layer BFT consensus protocol for large-scale IoT blockchain. We divide the nodes into groups, first reach consensus within the group, and then reach an overall consensus among the groups. This can convert the large-scale point-to-point broadcast into smaller ones and reduce communication overhead. To lower the energy consumption of communication inside the group, we utilize a simple clustering method to classify nodes that are close to each other into one group. It is worth noting that inter-group communication is more susceptible to outside interference. With the wisdom of asynchronous consensus algorithms, we propose weighted asynchronous byzantine agreement (WABA) to resist the influence of the long-distance message transfer time. Moreover, we adopt certificateless aggregate signatures to reduce communication and calculation cost during verification. The results of simulation experiments show that our protocol has substantially less communication overhead and lower latency than PBFT.