Network-Agnostic State Machine Replication

TL;DR

This paper introduces a network-agnostic state machine replication protocol that adapts to both synchronous and asynchronous networks, achieving optimal fault tolerance tradeoffs in the presence of malicious adversaries.

Contribution

It presents the first SMR protocol that seamlessly operates in both network models with optimal fault tolerance, bridging the gap between synchronous and asynchronous protocols.

Findings

Achieves optimal fault tolerance in both network models

Adapts seamlessly between synchronous and asynchronous environments

Supports malicious adversaries with high resilience

Abstract

We study the problem of state machine replication (SMR)---the underlying problem addressed by blockchain protocols---in the presence of a malicious adversary who can corrupt some fraction of the parties running the protocol. Existing protocols for this task assume either a synchronous network (where all messages are delivered within some known time $\Delta$) or an asynchronous network (where messages can be delayed arbitrarily). Although protocols for the latter case give seemingly stronger guarantees, this is not the case since they (inherently) tolerate a lower fraction of corrupted parties. We design an SMR protocol that is network-agnostic in the following sense: if it is run in a synchronous network, it tolerates $t_s$ corrupted parties; if the network happens to be asynchronous it is resilient to $t_a \leq t_s$ faults. Our protocol achieves optimal tradeoffs between $t_s$ and $t_a$.