Plume: Fast Finality Blockchain without Single Failure Point

Abstract

Bitcoin’s slow finality is an important factor preventing it from being widely used in real life. And other public single-chain blockchains have the same problem. In this paper, we propose a practical new protocol called Plume to achieve consensus with fast finality by utilizing a (slow) traditional blockchain. Plume combines the DAG structure and traditional blockchain to increase throughput and speed up confirmation. DAG structure is proposed to increase throughput, but how to construct a secure consensus protocol based on DAG is pretty hard. In Plume, we use the traditional blockchain to generate a randomness which is used to generate fast blocks in DAG. And the order of fast blocks in DAG is dependent on a global clock and a hash function. Same as bitcoin, Plume is a probabilistic protocol. However, due to DAG structure, the creation rate of blocks in Plume can be higher without reducing security. Thus the confirmation time of blocks can be accelerated. This paper also analyzes the probability of confirmation in different conditions and also proves that Plume is secure no matter the randomness from traditional single chain is unbiased or not. At last, this paper simulates performance with 1000 nodes using NS-3. The throughput can be improved to 400 Tps in the case that block size is 100K bytes and time interval of fast block is 1 second. Also the confirmation time can be reduced to within 2 minutes in the case that block size is 10K bytes and time interval is 1 second.