Byzantine Agreement with Unknown Participants and Failures

TL;DR

This paper demonstrates that Byzantine agreement can be achieved without prior knowledge of total participants or Byzantine faults, using new algorithms that operate under optimal resiliency in synchronous systems.

Contribution

It introduces Byzantine agreement algorithms that do not require knowledge of system size or Byzantine fault bounds, maintaining optimal resiliency in both static and dynamic systems.

Findings

Achieves Byzantine agreement without knowing total participants or fault bounds.

Provides algorithms for reliable broadcast, approximate agreement, and total ordering.

Shows synchrony is necessary for probabilistic termination without system size knowledge.

Abstract

A set of mutually distrusting participants that want to agree on a common opinion must solve an instance of a Byzantine agreement problem. These problems have been extensively studied in the literature. However, most of the existing solutions assume that the participants are aware of $n$ -- the total number of participants in the system -- and $f$ -- an upper bound on the number of Byzantine participants. In this paper, we show that most of the fundamental agreement problems can be solved without affecting resiliency even if the participants do not know the values of (possibly changing) $n$ and $f$. Specifically, we consider a synchronous system where the participants have unique but not necessarily consecutive identifiers, and give Byzantine agreement algorithms for reliable broadcast, approximate agreement, rotor-coordinator, early terminating consensus and total ordering in static and dynamic systems, all with the optimal resiliency of $n> 3f$. Moreover, we show that synchrony is necessary as an agreement with probabilistic termination is impossible in a semi-synchronous or asynchronous system if the participants are unaware of $n$ and $f$.