[论文解读] Brief Announcement: Grassroots Distributed Systems: Concept, Examples, Implementation and Applications

Ehud Shapiro|arXiv (Cornell University)|Jan 1, 2023

Distributed systems and fault tolerance被引用 3

一句话总结

本文提出基层分布式系统——一种去中心化、点对点的架构，允许自治的、可独立部署的社区在连接时实现互操作。它通过区块锁（blocklace，一种区块链的部分有序泛化）形式化了基层传播机制，并在异步、移动环境中证明了其正确性，从而实现抗审查、用户拥有的数字社交与经济系统，摆脱第三方控制。

ABSTRACT

Informally, a distributed system is grassroots if it is permissionless and can have autonomous, independently-deployed instances - geographically and over time - that may interoperate voluntarily once interconnected. More formally, in a grassroots system the set of all correct behaviors of a set of agents P is strictly included in the set of the correct behaviors of P when they are embedded within a larger set of agents P' ⊃ P. Grassroots systems are potentially important as they may allow communities to conduct their social, economic, civic, and political lives in the digital realm solely using their members' networked computing devices (e.g., smartphones), free of third-party control, surveillance, manipulation, coercion, or rent seeking (e.g., by global digital platforms such as Facebook or Bitcoin). Client-server/cloud computing systems are not grassroots, and neither are systems designed to have a single global instance (Bitcoin/Ethereum with hardwired seed miners/bootnodes), and systems that rely on a single global data structure (IPFS, DHTs). An example grassroots system would be a serverless smartphone-based social network supporting multiple independently-budding communities that can merge when a member of one community becomes also a member of another. Here, we formalize the notion of grassroots distributed systems; describe a grassroots dissemination protocol for the model of asynchrony and argue its safety, liveness, and being grassroots; extend the implementation to mobile (address-changing) devices that communicate via an unreliable network (e.g. smartphones using UDP); and discuss how grassroots dissemination can realize grassroots social networking and grassroots cryptocurrencies. The mathematical construction employs distributed multiagent transition systems to define the notions of grassroots protocols, to specify the grassroots dissemination protocols, and to prove their correctness. The protocols use the blocklace - a distributed, partially-ordered counterpart of the replicated, totally-ordered blockchain.

研究动机与目标

• 将基层系统形式化为支持自治、可独立部署社区的分布式架构。
• 设计并证明一种适用于异步、不可靠网络的基层传播协议的正确性。
• 实现实际应用，如去中心化的社交网络和货币，无需依赖中心化平台或全局协调。
• 将协议扩展至具有动态地址的移动设备，支持临时性、基于邻近的通信。

提出的方法

• 使用分布式多智能体转移系统形式化基层系统，以在部分连接条件下定义正确行为。
• 引入区块锁——一种分布式、部分有序的数据结构，作为区块链在异步、点对点传播中的泛化。
• 设计一种友好的传播协议，使智能体能够在无需全连接通信的情况下传播消息。
• 在异步环境下证明协议的正确性，并通过基于UDP的不可靠通信将协议扩展至移动设备。
• 采用“好友为基础”模型，智能体仅传播来自可信同伴的消息，从而降低通信开销。
• 通过回声/停止回声机制支持动态成员管理，实现群组或金融网络中智能体的添加与移除。

实验结果

研究问题

• RQ1 如何使分布式系统支持多个独立、自治的社区，仅在互联时实现互操作？
• RQ2 在不依赖全局协调的情况下，何种形式化条件可确保协议在更大网络中仍保持正确性？
• RQ3 如何在异步、不可靠、移动的环境中高效且正确地实现消息传播？
• RQ4 基层传播能否支持实际应用，如去中心化的社交网络和货币，而无需中心化信任或基础设施？
• RQ5 如何在无全局数据结构的情况下，在基层系统中强制实施隐私和访问控制？

主要发现

• 区块锁提供了区块链的正确、部分有序泛化，支持异步、去中心化的传播，无需总序要求。
• 基层传播协议确保智能体可无限期正确忽略外部智能体，同时在连接时仍能正确交互。
• 协议在异步环境下形式化证明正确，并扩展支持具有动态网络地址的移动设备。
• 通过群组创建者向好友传播消息，可实现基层社交网络，使群组通信呈现为单一消息线程。
• 通过代币赎回和基于好友的交易，可实现基层货币，协议支持可替代性与信用风险管控。
• 该系统通过允许用户完全在自有设备上运行，无需依赖云服务或中心化平台，实现数字主权。