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Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model

Authors Xuechao Wang , Sarah Azouvi , Marko Vukolić

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Author Details

Xuechao Wang
  • Thrust of Financial Technology, HKUST(GZ), Guangzhou, China
Sarah Azouvi
  • Protocol Labs, San Francisco, CA, USA
Marko Vukolić
  • Protocol Labs, San Francisco, CA, USA

Acknowledgements

The authors would like to thank Guy Goren for his suggestion of Consistent Broadcast as a mitigation to the n-split attack.

Cite AsGet BibTex

Xuechao Wang, Sarah Azouvi, and Marko Vukolić. Security Analysis of Filecoin’s Expected Consensus in the Byzantine vs Honest Model. In 5th Conference on Advances in Financial Technologies (AFT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 282, pp. 5:1-5:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)
https://doi.org/10.4230/LIPIcs.AFT.2023.5

Abstract

Filecoin is the largest storage-based open-source blockchain, both by storage capacity (>11EiB) and market capitalization. This paper provides the first formal security analysis of Filecoin’s consensus (ordering) protocol, Expected Consensus (EC). Specifically, we show that EC is secure against an arbitrary adversary that controls a fraction β of the total storage for β m < 1- e^{-(1-β)m}, where m is a parameter that corresponds to the expected number of blocks per round, currently m = 5 in Filecoin. We then present an attack, the n-split attack, where an adversary splits the honest miners between multiple chains, and show that it is successful for β m ≥ 1- e^{-(1-β)m}, thus proving that β m = 1- e^{-(1-β)m} is the tight security threshold of EC. This corresponds roughly to an adversary with 20% of the total storage pledged to the chain. Finally, we propose two improvements to EC security that would increase this threshold. One of these two fixes is being implemented as a Filecoin Improvement Proposal (FIP).

Subject Classification

ACM Subject Classification
  • Security and privacy → Distributed systems security
Keywords
  • Decentralized storage
  • Consensus
  • Security analysis

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References

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