Optimal Flexible Consensus and its Application to Ethereum

Joachim Neu; Srivatsan Sridhar; Lei Yang; David Tse

Paper 2023/1211

Optimal Flexible Consensus and its Application to Ethereum

Joachim Neu

, Stanford University

Srivatsan Sridhar

, Stanford University

Lei Yang

, Massachusetts Institute of Technology

David Tse

, Stanford University

Abstract

Classic BFT consensus protocols guarantee safety and liveness for all clients if fewer than one-third of replicas are faulty. However, in applications such as high-value payments, some clients may want to prioritize safety over liveness. Flexible consensus allows each client to opt for a higher safety resilience, albeit at the expense of reduced liveness resilience. We present the first construction that allows optimal safety-liveness tradeoff for every client simultaneously. This construction is modular and is realized as an add-on applied on top of an existing consensus protocol. The add-on consists of an additional round of voting and permanent locking done by the replicas, to sidestep a sub-optimal quorum-intersection-based constraint present in previous solutions. We adapt our construction to the existing Ethereum protocol to derive optimal flexible confirmation rules that clients can adopt unilaterally without requiring system-wide changes. This is possible because existing Ethereum protocol features can double as the extra voting and locking. We demonstrate an implementation using Ethereum's consensus API.

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Published elsewhere. Minor revision. IEEE Symposium on Security and Privacy 2024
Keywords: consensus blockchain
Contact author(s): jneu @ stanford edu
svatsan @ stanford edu
leiy @ csail mit edu
dntse @ stanford edu
History: 2023-12-06: revised; 2023-08-10: received; See all versions
Short URL: https://ia.cr/2023/1211
License: CC BY

BibTeX

@misc{cryptoeprint:2023/1211,
      author = {Joachim Neu and Srivatsan Sridhar and Lei Yang and David Tse},
      title = {Optimal Flexible Consensus and its Application to Ethereum},
      howpublished = {Cryptology {ePrint} Archive, Paper 2023/1211},
      year = {2023},
      url = {https://eprint.iacr.org/2023/1211}
}