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FairDAG: Consensus Fairness over Concurrent Causal Design

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Abstract

The rise of cryptocurrencies like Bitcoin and Ethereum has driven interest in blockchain technology, with Ethereum’s smart contracts enabling the growth of decentralized finance (DeFi). However, research has shown that adversaries exploit transaction ordering to extract profits through attacks like front-running, sandwich attacks, and liquidation manipulation. This issue affects both permissionless and permissioned blockchains, as block proposers have full control over transaction ordering. To address this, a more fair approach to transaction ordering is essential.

Main Idea

Apply the ideas from Themis (Batch-Fairness) and Pompe (Ordering Linearizability) into the DAG based consensus protocol, Narwhal.

My main take-away from this: How do they fix the performance bottleneck of ordering each transaction with each other in FairDAG-RL?

  • A: Looking at their code, they don’t! Ordering sometimes takes too long (around 48s).

Annotations

Kang et al. - 2025 - FairDAG Consensus Fairness over Concurrent Causal Design, p.8

For each vertex 𝑣𝑖,π‘Ÿ from replica 𝑅𝑖 in π·π‘Ÿ , we traverse the 𝑑𝑔𝑠. For each unordered transaction digest 𝑑 in 𝑑𝑔𝑠, we compare π‘›π‘œπ‘‘π‘’ (𝑑) with all other nodes in the same dependency graph 𝐺 by the value of π‘π‘œπ‘šπ‘–π‘‘π‘‘π‘’π‘‘_π‘œπ‘–π‘  [𝑖].

Isn’t this computationally taxing? It should cause a noticeable loss in throughput. Yeah that definitely is the case in their analysis as well.

Areas For Improvement

Transactions being included by all blocks results in a lot redundancy, which should impact the throughput very negatively. More specifically, inversely proportionally to the number of nodes.

BibTex

@misc{kangFairDAGConsensusFairness2025,
  author = {Kang, Dakai and Chen, Junchao and Dinh, Tien Tuan Anh and Sadoghi, Mohammad},
  title = {FairDAG: Consensus Fairness over Concurrent Causal Design},
  shorttitle = {FairDAG},
  year = {2025},
  month = {apr},
  number = {arXiv:2504.02194},
  doi = {10.48550/arXiv.2504.02194},
  publisher = {arXiv},
  eprint = {2504.02194},
  primaryclass = {cs},
  urldate = {2025-07-26},
  abstract = {The rise of cryptocurrencies like Bitcoin and Ethereum has driven interest in blockchain technology, with Ethereum's smart contracts enabling the growth of decentralized finance (DeFi). However, research has shown that adversaries exploit transaction ordering to extract profits through attacks like front-running, sandwich attacks, and liquidation manipulation. This issue affects both permissionless and permissioned blockchains, as block proposers have full control over transaction ordering. To address this, a more fair approach to transaction ordering is essential.},
  archiveprefix = {arXiv},
  langid = {english},
  keywords = {Computer Science - Cryptography and Security,Computer Science - Databases}
}

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