Consensus Under Adversary Majority Done Right

Srivatsan Sridhar; Ertem Nusret Tas; Joachim Neu; Dionysis Zindros; David Tse

Paper 2024/1799 Original: eprint.iacr.org/2024/1799 ↗

Consensus Under Adversary Majority Done Right

Srivatsan Sridhar

Ertem Nusret Tas

Joachim Neu

Dionysis Zindros

David Tse

Abstract

A specter is haunting consensus protocols—the specter of adversary majority. Dolev and Strong in 1983 showed an early possibility for up to 99% adversaries. Yet, other works show impossibility results for adversaries above 50% under synchrony, seemingly the same setting as Dolev and Strong's. What gives? It is high time that we pinpoint a key culprit for this ostensible contradiction: the modeling details of clients. Are the clients sleepy or always-on? Are they silent or communicating? Can validators be sleepy too? We systematize models for consensus across four dimensions (sleepy/always-on clients, silent/communicating clients, sleepy/always-on validators, and synchrony/partial-synchrony), some of which are new, and tightly characterize the achievable safety and liveness resiliences with matching possibilities and impossibilities for each of the sixteen models. To this end, we unify folklore and earlier results, and fill gaps left in the literature with new protocols and impossibility theorems.

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Preprint.
History: 2025-05-24: last updated; 2024-11-03: published
Short URL: https://ia.cr/2024/1799
License: https://creativecommons.org/licenses/by-nc-nd/4.0/

BibTeX

@misc{cryptoeprint:2024/1799,
      author = {Srivatsan Sridhar and Ertem Nusret Tas and Joachim Neu and Dionysis Zindros and David Tse},
      title = {Consensus Under Adversary Majority Done Right},
      howpublished = {Cryptology {ePrint} Archive, Paper 2024/1799},
      year = {2024},
      url = {https://eprint.iacr.org/2024/1799}
}