Collaborative Research:CNS Core:Medium:Unlinking the (Block)chain:Scalable Byzantine-Tolerant Databases.

该项目提出了一种新的架构，用于在相互不信任的各方之间实现安全可靠的数据共享。区块链如今是满足这种需求的首选平台。它们提供了共享的、完全有序的、防篡改的操作日志的吸引人的抽象，通过由一组计算节点运行的分布式协议实现，每个计算节点复制日志的整个状态。虽然这些协议的细节因区块链实现的不同而有所不同，但它们都依赖于底层架构，该架构受到两个关键限制。首先，它在执行模型上断言正确性和完整性，在该模型中，副本按照相同的总顺序顺序处理操作；这很快就成为性能瓶颈。其次，它使部署变得复杂。需要所有副本存储区块链中存储的全部数据不仅是资源密集型的，而且可能存在法律问题：例如，GDPR法律严格限制欧洲公民的个人可识别数据(如银行或医疗记录)可以驻留在哪里。该项目通过在新的基础上实施区块链抽象来克服这些限制，并通过这样做证明了高效的数据处理和信任的分散可以齐头并进。其核心是从以前的数据库研究中获得的一个关键见解-即，可以实现完全有序的事务序列的抽象，而不需要实际按顺序执行它们的所有操作。为了利用这一洞察力提供的更大并行性的机会，该项目将开发第一个地理分布式数据库，该数据库被证明对恶意破坏具有弹性，无论是来自实现数据库的一些计算节点还是来自数据库客户端的恶意破坏。今天，在这样的数据库中甚至没有关于正确性意味着什么的严格规范；这个项目将引入这样的正确性规范，基于限制恶意行为者(无论是在实现数据库的复制品之间还是在其客户端之间)对正确客户端提交的事务的结果所产生的影响的精神。然后，它将开发新的算法技术，尽管有相反的敌对尝试，但在可证明地强制执行这些正确性条件的同时，实现区块链抽象。为了简化部署，该项目将专注于大幅降低支持区块链所需的复制程度。具体地说，它将优化区块链当前的威胁模型，以确保不会丢失任何数据所需的复制程度与保证区块链执行的完整性所需的复制程度脱钩；这将使放松所有副本存储区块链的整个状态的要求成为可能，从而导致更容易的监管合规。相互不受信任的各方之间更紧密的集成可能会对各种应用程序产生变革，包括医疗保健、金融服务和供应链管理。数据库是支持这种集成的自然候选者，但目前缺乏一种在某些参与者恶意行为时表示和有效执行正确性的方法。这项工作构建了概念框架，利用了一种新的体系结构，使其更容易遵守数据使用规则，并在工作原型中实例化它，这些原型将被严格评估性能和健壮性。理论和工程之间的协同对于这个项目的成功至关重要，对下一代系统工程师的教育也是至关重要的：他们将不得不就性能、容错和对支撑当今大多数行业的无处不在的大规模分布式系统的信任问题进行谈判。建议的讲座和项目材料将使学生准备好应用原则性的方法来构建值得信赖的分布式系统。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project proposes a new architecture for enabling safe and secure data sharing among mutually distrustful parties. Blockchains are today the platform of choice for such needs. They offer the appealing abstraction of a shared, totally-ordered, tamper-resistant log of operations, implemented via a distributed protocol run by a collection of computing nodes, each replicating the entire state of the log. While the details of these protocols vary for different blockchain implementations, they all rely on an underlying architecture that suffers from two key limitations. First, it predicates correctness and integrity on an execution model where replicas process operations sequentially, according to the same total order; this quickly becomes a performance bottleneck. Second, it complicates deployment. The need for all replicas store the full body of data stored in the blockchain is not only resource intensive, but can be legally problematic: GDPR laws, for instance, severely restrict where personally identifiable data (such as banking or medical records) of European citizens can reside. This project overcomes these limitations by implementing the blockchain abstraction on a novel foundation, and, in so doing, demonstrates that efficient data processing and the decentralization of trust can go hand-in-hand. At its core is a key insight gained from prior research in databases – namely, that is possible to implement the abstraction of a totally ordered sequence of transactions without requiring all of their operations to be actually executed sequentially. To leverage the opportunity for greater parallelism offered by this insight, this project will develop the first geo-distributed database provably resilient to malicious sabotage, whether from some of the computing nodes implementing the database or from clients of the database. Today, there exists no rigorous specification of what correctness would even mean in such a database; this project will introduce such correctness specification, based on the ethos of bounding the influence that malicious actors (whether among the replicas implementing the database or among its clients) can have on the outcome of transactions submitted by correct clients. It will then develop new algorithmic techniques that, despite adversarial attempts to the contrary, implement the blockchain abstraction while provably enforcing these correctness conditions. To simplify deployment, this project will focus on drastically reducing the degree of replication necessary to support blockchains. Specifically, it will refine the blockchain’s current threat model to decouple the degree of replication needed to ensure that no data will be lost from what is required to guarantee the integrity of the blockchain execution; this will make it possible to relax the requirement that all replicas store the entire state of the blockchain, and thus lead to easier regulatory compliance. Tighter integration among mutually untrusted parties can be transformative for a variety of applications, including healthcare, financial services, and supply chain management. Databases are natural candidates for supporting this integration, but currently lack a way to express and efficiently enforce correctness when some actors behave maliciously. This work builds that conceptual framework, leveraging a novel architecture that makes it easier to comply with data use regulations, and instantiates it in working prototypes that will be rigorously evaluated for performance and robustness. The synergy between theory and engineering critical for the success of this project is also crucial to the education of the next generation of system engineers: they will have to negotiate issues of performance, fault-tolerance, and trust in the ubiquitous large-scale distributed systems that underpin most industries today. Proposed lecture and project materials will prepare students to apply a principled approach to building trustworthy distributed systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.