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：比特币是世界上最安全的链条,它得到其“劳动证据”采矿者巨大的散装力量的支持。 赌注链是节能的,具有快速的终局性,但面临若干安全问题:容易发生非大规模长距离安全攻击、低活性弹性和从低象征性估值中难以捕捉陷阱。 我们表明这些安全问题是任何POS链中固有的,没有外部信任的来源,并提议一个新的协议,即巴比特币,在比特币上设置一个现成的POS协议检查站。不可能的结果是巴比伦的最佳性。巴比伦的一个案例是减少保特提款延迟:我们的实验结果显示,利用巴比伦的现有POS链段的几周时间可以缩短到5小时以下,而比特币检查站的交易成本每年不到10美元。