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.

翻译：比特币是全球最安全的区块链，由其工作量证明（Proof-of-Work）矿工的巨大哈希能力支持。权益证明（Proof-of-Stake）链是能源效率高、最终性快，但面临多种安全问题：对非可减小的远程安全性攻击易受攻击、低活性弹性和难以从低代币估值处引导。我们展示这些安全问题是任何无可靠外部来源的PoS链所固有的，并提出了一种新协议Babylon，在比特币上对PoS协议进行检查点，以解决这些问题。一个不可能性结果证明巴比伦的最优性。Babylon的一个应用是缩短权益取回延迟：我们的实验结果显示，在Babylon的帮助下，这一延迟可以从现有PoS链中的几周缩短到不到5小时，发布到比特币的交易成本不到每年10,000美元。