Security-Performance Tradeoff in DAG-based Proof-of-Work Blockchain Protocols

Shichen Wu

Network and Distributed System Security (NDSS) Symposium 2024 · Day 2 · Blockchain & Smart Contracts

This talk presents a critical re-evaluation of the security guarantees in Directed Acyclic Graph (DAG)-based Proof-of-Work (PoW) blockchain protocols, specifically focusing on Prism and OHIE. These protocols emerged as promising solutions to overcome the inherent performance limitations—low transaction throughput and high confirmation latency—of Nakamoto Consensus (NC), as exemplified by Bitcoin. While NC's security relies on strict block size and interval bounds, DAG-based designs aim to increase throughput by allowing simultaneous block mining. Early DAG protocols often lacked rigorous security analyses, but Prism and OHIE stood out by claiming to achieve NC-like security (tolerance to nearly 50% adversarial mining power) almost independently of throughput, effectively breaking the fundamental security-performance tradeoff.