Blockchain protocols differ in fundamental ways, including the mechanics of selecting users to produce blocks (e.g., proof-of-work vs. proof-of-stake) and the method to establish consensus (e.g., longest chain rules vs. Byzantine fault-tolerant (BFT) inspired protocols). These fundamental differences have hindered "apples-to-apples" comparisons between different categories of blockchain protocols and, in turn, the development of theory to formally discuss their relative merits. This paper presents a parsimonious abstraction sufficient for capturing and comparing properties of many well-known permissionless blockchain protocols, simultaneously capturing essential properties of both proof-of-work (PoW) and proof-of-stake (PoS) protocols, and of both longest-chain-type and BFT-type protocols. Our framework blackboxes the precise mechanics of the user selection process, allowing us to isolate the properties of the selection process that are significant for protocol design. We demonstrate the utility of our general framework with several concrete results: 1. We prove a CAP-type impossibility theorem asserting that liveness with an unknown level of participation rules out security in a partially synchronous setting. 2. Delving deeper into the partially synchronous setting, we prove that a necessary and sufficient condition for security is the production of "certificates," meaning stand-alone proofs of block confirmation. 3. Restricting to synchronous settings, we prove that typical protocols with a known level of participation (including longest chain-type PoS protocols) can be adapted to provide certificates, but those with an unknown level of participation cannot. 4. Finally, we use our framework to articulate a modular two-step approach to blockchain security analysis that effectively reduces the permissionless case to the permissioned case.

中文翻译：

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区块链协议安全分析的通用框架

区块链协议在基本方面有所不同，包括选择用户生成区块的机制（例如，工作量证明与权益证明）和建立共识的方法（例如，最长链规则与拜占庭容错） （BFT）启发的协议）。这些根本差异阻碍了不同类别区块链协议之间的“逐个”比较，进而阻碍了正式讨论其相对优点的理论的发展。本文提出了一种简洁的抽象，足以捕获和比较许多著名的无许可区块链协议的属性，同时捕获工作量证明 (PoW) 和权益证明 (PoS) 协议的基本属性，以及最长的-chain-type 和 BFT-type 协议。我们的框架黑盒了用户选择过程的精确机制，使我们能够隔离对协议设计很重要的选择过程的属性。我们通过几个具体结果证明了我们的通用框架的实用性： 1. 我们证明了一个 CAP 类型的不可能性定理，该定理断言具有未知参与水平的活跃性排除了部分同步设置中的安全性。2. 深入研究部分同步设置，我们证明安全的必要和充分条件是“证书”的产生，即区块确认的独立证明。3. 限于同步设置，我们证明了具有已知参与度的典型协议（包括最长链式 PoS 协议）可以适用于提供证书，但是那些参与程度未知的人不能。4. 最后，我们使用我们的框架来阐明区块链安全分析的模块化两步方法，有效地将无许可情况减少到许可情况。