Adapted PBFT Consensus Protocol for Sharded Blockchain

As the foundation of a blockchain, consensus algorithm significantly affects the blockchain system’s performance. To a consortium blockchain, Practical Byzantine Fault Tolerance (PBFT) has been widely believed as a good candidate consensus due to its many advantages. However, PBFT is not particularly designed for a consortium blockchain. Thus, there is still a large improvement space to implement the PBFT algorithm in a sharded blockchain. Based on network sharding, we aim to address the problems incurred by the traditional PBFT algorithm. Because when there are large number of nodes in a P2P network, PBFT can lead to a significant performance degradation. Even worse, Byzantine nodes cannot be found timely in a large-scale blockchain network where the PBFT algorithm is adopted. In this paper, we propose an adapted version of BFT consensus for the sharded blockchain. The proposed cross-shard BFT consensus mainly consists of a two-phase consensus mechanism after performing network sharding. In the first phase, Raft consensus is first adopted within each shard, in which a leader is elected. In the second phase, those leaders from all shards form a committee and perform a committee-wise PBFT consensus. Through introducing anchor nodes within each shard, the security of the proposed two-phase consensus is guaranteed. We analyze the security of the cross-shard BFT consensus based on a committee-wise monitoring framework. Through simulations, we find out that the proposed cross-shard BFT consensus yields a higher throughput, lower latency than the original PBFT. The fault-tolerance ability of the proposed consensus is around 1.5$\times$ to 2$\times$ of PBFT.