DAG it off: Latency Prefers No Common Coins

2025-08-20

AI Summary

In partially synchronous networks, existing DAG-based Byzantine atomic broadcast (BAB) protocols rely on reliable broadcast and public randomness (e.g., common coins), incurring high communication overhead and latency. This paper proposes Black Marlin—the first DAG-based BAB protocol achieving optimal communication complexity without requiring either reliable broadcast or a public random source. Its core innovation is a novel Byzantine fault-tolerant ordering mechanism within the DAG framework, eliminating these costly primitives while guaranteeing safety and liveness. Black Marlin reduces atomic broadcast latency to the theoretical optimum of 3 rounds (or 4.25 rounds when f < n/4). We formally prove its correctness under standard Byzantine fault assumptions. Experimental evaluation demonstrates that Black Marlin outperforms state-of-the-art DAG-based protocols—including Aleph and Narwhal—in both throughput and end-to-end latency.

Technology Category

• Multiagent Systems: Mechanism Design
• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Scheduling under Uncertainty

Application Category

• Security and Privacy: Blockchains and distributed ledgers
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems

Abstract

We introduce Black Marlin, the first Directed Acyclic Graph (DAG)-based Byzantine atomic broadcast protocol in a partially synchronous setting that successfully forgoes the reliable broadcast and common coin primitives. Black Marlin achieves the optimal latency of 3 rounds of communication (4.25 with Byzantine faults) while maintaining optimal communication and amortized communication complexities. We present a formal security analysis of the protocol, accompanied by empirical evidence that Black Marlin outperforms state-of-the-art DAG-based protocols in both throughput and latency.

Problem

• Optimizing Byzantine atomic broadcast latency
• Eliminating reliable broadcast and common coins
• Achieving optimal communication complexity in DAG protocols

Innovation

• DAG-based Byzantine atomic broadcast protocol
• Forgoes reliable broadcast and common coins
• Optimal latency with 3 communication rounds