Optimal Bootstrapping of PoW Blockchains (2208.10618v1)

Abstract: Proof of Work (PoW) blockchains are susceptible to adversarial majority mining attacks in the early stages due to incipient participation and corresponding low net hash power. Bootstrapping ensures safety and liveness during the transient stage by protecting against a majority mining attack, allowing a PoW chain to grow the participation base and corresponding mining hash power. Liveness is especially important since a loss of liveness will lead to loss of honest mining rewards, decreasing honest participation, hence creating an undesired spiral; indeed existing bootstrapping mechanisms offer especially weak liveness guarantees. In this paper, we propose Advocate, a new bootstrapping methodology, which achieves two main results: (a) optimal liveness and low latency under a super-majority adversary for the Nakamoto longest chain protocol and (b) immediate black-box generalization to a variety of parallel-chain based scaling architectures, including OHIE and Prism. We demonstrate via a full-stack implementation the robustness of Advocate under a 90% adversarial majority.

• The paper introduces Advocate, a novel bootstrapping protocol that secures Nakamoto consensus against super-majority adversaries with optimal liveness and low latency.
• It demonstrates how checkpoint certificates and adaptable BFT integration maintain high chain quality even when adversaries control up to 90% of mining power.
• The methodology is adaptable to parallel-chain protocols like OHIE and Prism, highlighting its practical significance for scalable, secure PoW systems.

Optimal Bootstrapping of PoW Blockchains: An Analysis

This paper focuses on the challenge of securely bootstrapping Proof of Work (PoW) blockchains, particularly in their nascent stages when adversarial actors could potentially exploit low participation and hash power. The central contribution of the paper is a novel bootstrapping methodology, named Advocate, which aims to assure both safety and liveness against a super-majority mining adversary. This work addresses a critical need for robust PoW systems susceptible to early attacks due to low initial participation.

Key Contributions

1. Bootstrapping Methodology: The Advocate protocol provides a mechanism to achieve optimal liveness and low latency under a super-majority adversary scenario for the Nakamoto longest chain protocol. It does so by utilizing checkpoint certificates that reference blocks not on the main chain, ensuring the inclusion of all blocks, thus maintaining chain quality.
2. Generalization to Parallel-Chain Protocols: The authors propose that the methodology is easily adaptable to parallel-chain based scaling architectures like OHIE and Prism. This adaptability is significant because these architectures are designed to improve throughput, making their security paramount in adversarial environments.
3. BFT Integration: Advocate successfully extends from a centralized approach to a distributed system using Byzantine Fault Tolerant (BFT) consensus, allowing for decentralized checkpointing. This integration addresses centralization concerns by using a committee-based approach to consensus, ensuring that an adversarial majority cannot compromise system integrity.
4. Theoretical and Empirical Analysis: Through both theoretical proofs and empirical testing, Advocate is shown to provide optimal chain quality even in scenarios where adversaries control a 90% mining majority. This is critical as it demonstrates the protocol’s resilience and effectiveness in potential real-world adversarial settings.

Implications and Future Directions

The implications of this work are profound for the development and adoption of secure PoW systems, particularly in ensuring they can withstand initial vulnerabilities. By guaranteeing optimal chain quality and block inclusion under adversarial conditions, the Advocate methodology sets a new standard in PoW blockchain security.

From a theoretical perspective, future research could explore further refinement of BFT protocols to ensure even greater efficiency and lower latency in blockchain environments. Practically, the findings suggest promising avenues for the deployment of PoW systems in environments previously considered high-risk due to their susceptibility to adversarial attacks.

In addition, the success of Advocate in integrating with high-throughput systems like Prism highlights the potential for developing adaptable protocols that maintain security across varying blockchain architectures. Future exploration could involve extending these findings to other consensus mechanisms or enhancing throughput without compromising security guarantees.

Conclusion

The paper presents a comprehensive solution to the critical challenge of bootstrapping PoW blockchains in adversarial settings, achieving a balance between decentralization, security, and efficiency. By focusing on adaptable and robust checkpointing methodologies, the work offers valuable insights for both researchers and practitioners aiming to enhance the resilience of blockchain systems. The findings advance the field by reinforcing the importance of secure bootstrapping and setting the stage for future innovations in blockchain technology.