The Dolev-Reischuk bound says that any deterministic Byzantine consensus protocol has (at least) quadratic communication complexity in the worst case. While it has been shown that the bound is tight in synchronous environments, it is still unknown whether a consensus protocol with quadratic communication complexity can be obtained in partial synchrony. Until now, the most efficient known solutions for Byzantine consensus in partially synchronous settings had cubic communication complexity (e.g., HotStuff, binary DBFT). This paper closes the existing gap by introducing SQuad, a partially synchronous Byzantine consensus protocol with quadratic worst-case communication complexity. In addition, SQuad is optimally-resilient and achieves linear worst case latency complexity. The key technical contribution underlying SQuad lies in the way we solve view synchronization, the problem of bringing all correct processes to the same view with a correct leader for sufficiently long. Concretely, we present RareSync, a view synchronization protocol with quadratic communication complexity and linear latency complexity, which we utilize in order to obtain SQuad.
A decision task is a distributed input-output problem in which each process starts with its input value and eventually produces its output value. Examples of such decision tasks are broad and range from consensus to reliable broadcast to lattice agreement. A distributed protocol solves a decision task if it enables processes to produce admissible output values despite arbitrary (Byzantine) failures. Unfortunately, it has been known for decades that many decision tasks cannot be solved if the system is overly corrupted, i.e., safety of distributed protocols solving such tasks can be violated in unlucky scenarios.By contrast, only recently did the community discover that some of these distributed protocols can be made accountable by ensuring that correct processes irrevocably detect some faulty processes responsible for any safety violation. This realization is particularly surprising (and positive) given that accountability is a powerful tool to mitigate safety violations in distributed protocols. Indeed, exposing crimes and introducing punishments naturally incentivize exemplarity.In this paper, we propose a generic transformation, called τscr , of any non-synchronous distributed protocol solving a decision task into its accountable version. Our τscr transformation is built upon the well-studied simulation of crash failures on top of Byzantine failures and increases the communication complexity by a quadratic multiplicative factor in the worst case.
In a non-synchronous system with n processes, no t 0 -resilient (deterministic or probabilistic) Byzantine consensus protocol can prevent a disagreement among correct processes if the number of faulty processes is ≥ n − 2t 0 . Therefore, the community defined the accountable Byzantine consensus problem: the problem of (i) solving Byzantine consensus whenever possible (e.g., when the number of faulty processes does not exceed t 0 ), and (ii) allowing correct processes to obtain proofs of culpability of n − 2t 0 faulty processes whenever a disagreement occurs. This paper presents ABC, a simple yet efficient transformation of any non-synchronous t 0 -resilient (deterministic or probabilistic) Byzantine consensus protocol into its accountable counterpart. In the common case (up to t 0 faults), ABC introduces an additive overhead of two communication rounds and O (n 2 ) exchanged bits. Whenever they disagree, correct processes detect culprits by exchanging O (n 3 ) messages, which we prove optimal. Lastly, ABC is not limited to Byzantine consensus: ABC provides accountability for other essential distributed problems (e.g., reliable and consistent broadcast).
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.