CAREER: Decentralizing Trust in Open Distributed Systems

允许任何用户将其节点注册为参与者的分布式系统必须解决两个主要挑战以实现可靠性：选择值得信赖的参与者，以及检测和控制异常节点的损害。本研究通过以下方式解决了这些挑战：(a)提出了一种新的系统架构F2F，该架构在确定可信赖节点时结合了用户之间分散的信任关系；(b)设计了新技术来检测和包含使用这种新架构的具体应用环境中行为不端的节点的故障。本研究通过设计和实现两个案例研究系统：合作备份和审查规避，证明了F2F的有用性。Friendstore通过将每个用户的数据存储在可信任的邻居的子集上，提供廉价而可靠的备份。这样的架构允许friendstore使用成本较低的技术手段来检测和恢复故障，但却使其难以充分利用存储资源。该项目使用编码技术解决了这一挑战，该技术允许节点同时有效地为多个相邻节点提供数据冗余。第二个案例研究系统“万花筒”（Kaleidoscope）通过代理网络转发流量，帮助被审查域名内的用户访问被屏蔽的网站。万花筒使用一种新颖的协议在F2Ftrust图上传播代理身份，这样每个节点只能收集关于其他节点身份的有限信息。因此，少数恶意节点无法发现大部分代理。如果成功部署，该项目将产生为家庭用户提供廉价在线存储的系统，并帮助数百万受影响的用户规避审查。

Distributed systems that allow any user to enroll his node as a participantmust resolve two main challenges to achieve reliability: selecting trustworthyparticipants, and detecting and containing the damage of deviant nodes. Thisresearch addresses these challenges by (a) presenting a new systemarchitecture, F2F, that incorporates decentralized trust relationships amongusers in determining trustworthy nodes and (b) devising new techniques todetect and contain faults of misbehaving nodes in the context of concreteapplications using this new architecture. This research demonstrates the usefulness of F2F through the design andimplementation of two case-study systems: cooperative backup and censorshipcircumvention. Friendstore provides inexpensive and reliable backup by storingeach user's data on a subset of trusted neighbors. Such an architecture allowsFriendstore to use less expensive technical means to detect and recover fromfaults but makes it harder to fully utilize storage resources. This project addresses this challenge using coding techniques that allow a node toefficiently provide data redundancy for multiple neighbors simultaneously. Thesecond case study system, Kaleidoscope, helps users inside censored domainsaccess blocked websites by relaying traffic via a network of proxies.Kaleidoscope uses a novel protocol to disseminate proxy identities over the F2Ftrust graph so that each node can only collect limited information aboutothers' identities. A few malicious nodes, then, cannot discover a significantfraction of proxies. This project will produce systems that, if successfully deployed, provideinexpensive online storage to home users and help circumvent censorship formillions of affected users.