Tilikum: Transaction Fair Ordering on a DAG without Weak Edges

2026-06-25

AI Summary

This work addresses the lack of effective fair transaction ordering mechanisms in DAG-based blockchains, which renders them vulnerable to reordering attacks and blockchain-extractable value (BEV) exploitation. The paper proposes a novel DAG ledger protocol that, for the first time, achieves strong order fairness without relying on weak-edge structures. By integrating median timestamp aggregation with a batching fairness mechanism, the protocol ensures linearizable transaction ordering while maintaining low data redundancy and enabling efficient garbage collection. A Rust-based implementation demonstrates up to a 39× throughput improvement over state-of-the-art baselines—including Narwhal/Tusk, Pompē, Themis, and FairDAG—and completely mitigates known DAG-specific reordering attacks.

Abstract

Decentralized Finance (DeFi) applications rely heavily on the order in which transactions are executed, making them susceptible to reordering attacks that enable adversaries to extract Blockchain Extractable Value (BEV). While linear blockchain systems such as Ethereum have inspired extensive research into fair ordering mechanisms, DAG-based consensus protocols have remained largely unprotected despite their growing adoption for scalability and performance. In this paper, we introduce Tilikum, a DAG-based ledger protocol that ensures fair transaction ordering without relying on weak edges. Tilikum achieves ordering linearizability by leveraging median-based timestamp aggregation, or batch order fairness, while maintaining low data redundancy and robust garbage collection. We implemented Tilikum in Rust and evaluated it against representative baselines, namely Narwhal/Tusk, Pompē, Themis and FairDAG. Our results show that Tilikum achieves up to $39\times$ higher throughput than other fair-ordering baselines, while fully blocking state-of-the-art DAG-specific reordering attacks.

Problem

• fair ordering
• reordering attacks
• DAG-based consensus
• Blockchain Extractable Value
• transaction ordering

Innovation

• fair ordering
• DAG-based consensus
• reordering attacks
• median-based timestamp
• Blockchain Extractable Value