Validated Strong Consensus Protocol for Asynchronous Vote-based Blockchains

TL;DR

This paper introduces a scalable, asynchronous Byzantine Fault Tolerance consensus protocol for vote-based blockchains that reduces message complexity and enables large-scale deployment.

Contribution

It proposes a validated strong BFT consensus model allowing leader-based coordination in asynchronous settings, with a protocol achieving linear view changes without threshold signatures.

Findings

Achieves the same fault tolerance as binary Byzantine agreement.

Reduces message complexity significantly.

Enables large-scale asynchronous blockchain deployment.

Abstract

Vote-based blockchains construct a state machine replication (SMR) system among participating nodes, using Byzantine Fault Tolerance (BFT) consensus protocols to transition from one state to another. Currently, they rely on either synchronous or partially synchronous networks with leader-based coordination or costly Asynchronous Common Subset (ACS) protocols in asynchronous settings, making them impractical for large-scale asynchronous applications. To make Asynchronous SMR scalable, this paper proposes a \emph{validated strong} BFT consensus model that allows leader-based coordination in asynchronous settings. Our BFT consensus model offers the same level of tolerance as binary byzantine agreement but does not demand consistency among honest nodes before they vote. An SMR using our model allows nodes to operate in different, tentative, but mutually exclusive states until they eventually converge on the same state. We propose an asynchronous BFT protocol for vote-based blockchains employing our consensus model to address several critical challenges: how to ensure that nodes eventually converge on the same state across voting rounds, how to assure that a blockchain will steadily progress through epochs while reaching consensus for previous epochs, and how to maintain robust byzantine fault tolerance. Our protocol greatly reduces message complexity and is the first one to achieve linear view changes without relying on threshold signatures. We prove that an asynchronous blockchain built on our protocol can operate with the \emph{same} simplicity and efficiency as partially synchronous blockchains built on, e.g. HotStuff-2. This facilitates deploying asynchronous blockchains across large-scale networks.