Bitcoin-Enhanced Proof-of-Stake Security: Possibilities and Impossibilities

2022-07-18

IEEE Symposium on Security and Privacy

AI Summary

Proof-of-Stake (PoS) blockchains face fundamental security challenges—including long-range attacks, low liveness, and cold-start vulnerabilities—due to their reliance on internal consensus without external trust anchors. Method: This paper introduces Babylon, a protocol that establishes a trustless security anchor for PoS chains by posting lightweight, aggregated checkpoints onto the Bitcoin blockchain via OP_RETURN outputs, leveraging checkpoint compression, threshold signature aggregation, and on-chain verification. Crucially, it requires no modification to the underlying PoS protocol and enables plug-and-play deployment. Contribution/Results: Babylon provides the first formal characterization of the trustless security limits of PoS systems and presents a theoretically optimal Bitcoin-augmented security architecture. It delivers strong finality and long-range attack resistance while reducing stake withdrawal delays from weeks to under five hours and keeping annual checkpoint publication costs below $10,000—scalable to any standard PoS chain. The work also includes an impossibility proof for certain security guarantees under minimal assumptions.

Abstract

Bitcoin is the most secure blockchain in the world, supported by the immense hash power of its Proof-of-Work miners. Proof-of-Stake chains are energy-efficient, have fast finality but face several security issues: susceptibility to non-slashable long-range safety attacks, low liveness resilience and difficulty to bootstrap from low token valuation. We show that these security issues are inherent in any PoS chain without an external trusted source, and propose a new protocol, Babylon, where an off-the-shelf PoS protocol checkpoints onto Bitcoin to resolve these issues. An impossibility result justifies the optimality of Babylon. A use case of Babylon is to reduce the stake withdrawal delay: our experimental results show that this delay can be reduced from weeks in existing PoS chains to less than 5 hours using Babylon, at a transaction cost of less than 10K USD per annum for posting the checkpoints onto Bitcoin.

Problem

• Proof of Stake
• Blockchain Security
• Token Value

Innovation

• Babylon
• Proof of Stake (PoS) Security Enhancement
• Bitcoin Checkpoints Optimization