Travelers: A scalable fair ordering BFT system
Bowen Xue, Sreeram Kannan
TL;DR
Travelers tackles the blockchain fairness gap caused by MEV by introducing probabilistic order fairness, a relaxed yet robust ordering guarantee for BFT systems. It combines a novel routing protocol over hubs with timestamp locking to decouple routing from consensus, achieving sublinear transaction-submission costs while preserving a total order via a canonical timestamp. The main contributions include the probabilistic ordering linearizability notion, a detailed routing design with boosting techniques, and two practical variants (Travelers-Speed and Travelers-Light) that reduce communication while maintaining censorship resistance. The work's significance lies in delivering scalable fair ordering for distributed ledgers, reducing defense costs against MEV attacks and enabling flexible integration with existing BFT protocols and cryptographic techniques like threshold encryption.
Abstract
Many blockchain platform are subject to maximal value extraction (MEV), and users on the platform are losing money while sending transactions because the transaction order can be manipulated to extract value from them. Consensus protocols have been augmented with different notion of fair ordering in order to counter the problem. Out of all practical protocols, the most efficient BFT consensus requires $O(nTL + n^2T)$ communication complexity, where $n$ is number node, $T$ is number of transactions and $L$ is average transaction size. In this work, we propose a new system of BFT fair ordering protocols, Travelers, that substantially reduce the communication complexity. The proposed system of protocols satisfy a new notion of fair ordering, called probabilistic fair ordering, which is an extension to some existing notions of fairness. The new notion allows a small probability of error $ε$, that adversary can insert some transactions at any location in a block, but for the remaining $1-ε$ the a modified version of ordering linearizability holds. Our mechanism neither require a dissemination network nor direct submissions to all consensus nodes. The key innovation comes from a routing protocol, that is both flexible and efficient. We construct a protocol with $O(c\log({n})TL + n^2)$ communication complexity with $ε= 1/n^c$ for some system parameter $c\ge 1$.