MSig-BFT: A Witness-Based Consensus Algorithm for Private Blockchains

In this paper, we focus on the design of consensus algorithms for permission-based blockchains, i.e., private blockchains. In most consensus algorithms, blocks are proposed by a specific role called “leader”. In this paper, we introduce a new role called “witness” to supervise the leader. The presence of the witness facilitates the design of the consensus algorithm. We propose a witness-based consensus algorithm that guarantees safety and liveness. We implemented this consensus algorithm on Go Ethereum. The experimental result shows that in a blockchain where four nodes participate in the consensus process, we can achieve a throughput of 1000 transactions per second (TPS). Even if these four nodes are located on different continents, and one of them is faulty, we can still achieve a throughput of 300 TPS. Finally, we find that during the experiment, a significant portion of time is spent on activities other than the consensus task. The result suggests that to further increase the throughput of a private blockchain, the consensus task and non-consensus activities should be considered jointly.

I. Introduction

Satoshi Nakamoto proposed the idea of blockchains in 2008 [1]. Since then, blockchains have become a general decentralized database technology, whose applications are no longer limited to cryptocurrency. In blockchains such as Bitcoin, anyone can join the blockchain. Specifically, anyone has the opportunity to generate blocks and to append the generated block to the blockchain. Such a blockchain does not employ admission control, and thus is called a public blockchain. However, in some scenarios, such as a blockchain maintained by a consortium of banks, the blockchain is maintained privately and only specific participants have the right to join it. Such blockchains are called private blockchains.