PlainDAG: A Low-Latency Asynchronous DAG BFT Protocol With Best-Effort Broadcast

Broadcast primitives like Reliable Broadcast (RBC) are integral to Directed Acyclic Graph (DAG)-based asynchronous Byzantine Fault Tolerant (BFT) protocols. Despite recent advancements, these protocols often suffer from high latency due to the inherent three communication rounds in RBC. To mitigate this latency, we propose employing Best-Effort Broadcast (BBC) for message dissemination, which requires only one communication round. However, leveraging BBC poses challenges in constructing a DAG-based ledger and ensuring consistent commitment in the face of contradictory blocks. In this paper, we introduce PlainDAG, a low-latency and secure asynchronous DAG-based BFT protocol that eschews complex broadcast primitives. Instead, it achieves lower latency by simplifying broadcast and committing with a larger quorum of votes. Our approach addresses the integrity, agreement, and totality properties lacking in BBC compared to RBC, thus ensuring correctness. Key to the design of PlainDAG is the introduction of an Integral Reference field in blocks, which References previously committed blocks and facilitates voting among contradictory blocks. Additionally, we devise a block query scheme to retrieve missing blocks. Theoretical analysis demonstrates the generalized design applicability of PlainDAG for asynchronous DAG-based BFT, with the best-case latency of 2 communication rounds and practical resilience. Experimental results underscore the superiority of PlainDAG over state-of-the-art asynchronous DAG-based protocols in latency, while achieving comparable throughput performance.