Quick Order Fairness

TL;DR

This paper introduces a new, efficient protocol for order fairness in atomic broadcast, addressing limitations of previous solutions and ensuring differentially fair message ordering in blockchain and decentralized finance systems.

Contribution

We propose a novel differential order fairness property and a quick, more efficient atomic broadcast protocol that tolerates up to one-third process failures in asynchronous networks.

Findings

Guarantees payload message delivery in a differentially fair order.

Achieves quadratic message complexity, improving efficiency.

Supports asynchronous and eventually synchronous networks with optimal resilience.

Abstract

Leader-based protocols for consensus, i.e., atomic broadcast, allow some processes to unilaterally affect the final order of transactions. This has become a problem for blockchain networks and decentralized finance because it facilitates front-running and other attacks. To address this, order fairness for payload messages has been introduced recently as a new safety property for atomic broadcast complementing traditional agreement and liveness. We relate order fairness to the standard validity notions for consensus protocols and highlight some limitations with the existing formalization. Based on this, we introduce a new differential order fairness property that fixes these issues. We also present the quick order-fair atomic broadcast protocol that guarantees payload message delivery in a differentially fair order and is much more efficient than existing order-fair consensus protocols. It works for asynchronous and for eventually synchronous networks with optimal resilience, tolerating corruptions of up to one third of the processes. Previous solutions required there to be less than one fourth of faults. Furthermore, our protocol incurs only quadratic cost, in terms of amortized message complexity per delivered payload.