Concordia: A Streamlined Consensus Protocol for Blockchain Networks

Abstract

In this paper, we present a novel Byzantine fault-tolerant consensus protocol for sharded blockchain networks that does not rely on expensive leader-driven communication. The proposed protocol selects a single block proposer at a time and uses threshold signatures as a voting mechanism to confirm the validity of the proposed block. By using a gossip-like communication scheme, each node can collect and recover the group signature within$\mathrm {O(log}N)$steps. With only one block proposer per consensus round, there is no possibility of conflicting blocks and resultant forks. Therefore, our consensus protocol requires only one round of one-way communication to achieve finality for each block. Our protocol guarantees safety and liveness while tolerating up to$f$faulty participants among$2f+1$nodes. Our performance study shows that the proposed protocol enables hundreds of nodes to participate in the agreement process, and can finalize large blocks in approximately 10 seconds.