DAG-based Consensus with Asymmetric Trust [Extended Version]

2025-05-23

AI Summary

Existing DAG-based consensus protocols (e.g., DAG-Rider) rely on symmetric trust assumptions, rendering them incompatible with asymmetric trust models—where nodes independently define their trust relationships—and causing core primitives (e.g., *gather*) to fail. Method: We propose the first DAG-based consensus protocol tailored for asynchronous, asymmetric trust settings. Our approach introduces a novel asymmetric common core computation mechanism, integrating heterogeneous quorums, an extended DAG-Rider architecture, randomized Byzantine fault tolerance, and asynchronous consensus techniques. Contribution: The protocol achieves expected constant-round decision latency—where round complexity is determined solely by the quorum structure—supports arbitrary asymmetric trust configurations, and strictly guarantees safety and liveness in fully asynchronous networks. It overcomes the fundamental limitations of threshold-based protocols in asymmetric settings, enabling robust consensus without requiring global trust symmetry.

Technology Category

• Multiagent Systems: Mechanism Design
• Data Mining & Knowledge Management: Representing, Reasoning, and Using Provenance, Trust
• Game Theory and Economic Paradigms: Fair Division

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Economics, Online Markets and Human Computation: Trust and reliance of crowd workers and data experts on GenAI

Abstract

In protocols with asymmetric trust, each participant is free to make its own individual trust assumptions about others, captured by an asymmetric quorum system. This contrasts with ordinary, symmetric quorum systems and with threshold models, where all participants share the same trust assumption. It is already known how to realize reliable broadcasts, shared-memory emulations, and binary consensus with asymmetric quorums. In this work, we introduce Directed Acyclic Graph (DAG)-based consensus protocols with asymmetric trust. To achieve this, we extend the key building-blocks of the well-known DAG-Rider protocol to the asymmetric model. Counter to expectation, we find that replacing threshold quorums with their asymmetric counterparts in the existing constant-round gather protocol does not result in a sound asymmetric gather primitive. This implies that asymmetric DAG-based consensus protocols, specifically those based on the existence of common-core primitives, need new ideas in an asymmetric-trust model. Consequently, we introduce the first asymmetric protocol for computing a common core, equivalent to that in the threshold model. This leads to the first randomized asynchronous DAG-based consensus protocol with asymmetric quorums. It decides within an expected constant number of rounds after an input has been submitted, where the constant depends on the quorum system.

Problem

• Develop DAG-based consensus with asymmetric trust
• Extend DAG-Rider protocol to asymmetric model
• Create first asymmetric common-core protocol

Innovation

• DAG-based consensus with asymmetric trust
• Extends DAG-Rider protocol to asymmetric model
• Introduces first asymmetric common-core protocol