FleetChain: A Secure Scalable and Responsive Blockchain Achieving Optimal Sharding

Sharding blockchains are promising in improving transaction throughput and achieving network scalability. Intra-shard consensus and cross-shard communication are two essential parts for almost every kind of sharding blockchain. However, some security problems still exist in current sharding solutions such as replay attacks, and there is still room for improvement in efficiency. In this paper, we propose FleetChain, a secure and scalable sharding blockchain. First, we make modification of the original BLS multi-signature scheme to a robust (t, u)-multi-signature protocol supporting further aggregation, which could shorten vote messages. Second, a leader-stable fast Byzantine fault tolerance (FBFT) protocol is designed for efficient intra-shard consensus, combining pipeline technology and multi-signature. FBFT is specially designed for sharding blockchains, with the ability to process different types of proposals that might be transactions or transaction inputs. Third, a responsive sharding transaction processing (RSTP) protocol is given, which greatly improves the processing efficiency of cross-shard transactions by using multi-signature aggregation. FleetChain employs a star network in both intra-shard and cross-shard communication, achieving responsiveness when confirming transactions. In addition, FleetChain achieves optimal sharding with a scaling factor of O(n/ log n) where n denotes the total number of participating nodes.