SaTC-BSF: CORE: Small: Collaborative: Making Blockchains Scale Privately and Reliably

这项研究探索了同时提高区块链技术的可扩展性和隐私的方法。区块链是一种大规模分布的、仅附加的交易日志，通过密码保护不会被篡改。由于区块链在全球范围内促进快速、廉价交易的能力，以及对复杂金融工具的强大脚本语言支持，区块链已被证明是金融和电子商务领域的一股高度颠覆性力量。然而，至少有两个主要障碍仍然阻碍着主流区块链的接受：1)传统的区块链架构没有足够的可扩展性来应对不断增长的区块链用户群和随之而来的交易激增，2)尽管付出了无数努力来改善区块链隐私，但公共区块链的用户仍然容易受到对其账户和交易隐私的毁灭性攻击，这往往会导致安全漏洞，给受害者造成经济损失。本项目中探索的方法为区块链用户提供隐私，此前的努力通过重新考虑使用Tor来解决所有需要匿名性和/或不可链接的问题的一刀切方法而失败。事实上，在Tor上运行复杂的协议充满了风险，可能会让用户面临微妙但毁灭性的反匿名化攻击；该项目开发的定制解决方案利用特定领域的知识来缓解这些风险。该项目解决了隐私问题，因为它们与传统的区块链交易和较新的“支付渠道网络”交易有关。支付渠道网络允许安全(离链)支付，无需与区块链分类账交互，从而承诺极大地提高可扩展性。在传统区块链交易的背景下，本研究开发了创新的方法：1)通过将定制的匿名通信协议直接集成到区块链通信基础设施中，将交易私下发布到区块链；2)使用经过精心优化的支持可表达的区块链查询的私人信息检索(PIR)协议，私下从区块链中检索交易。在支付渠道网络的背景下，该项目1)探索私下进行离链交易的可能性，2)开发新的理论框架和算法工具包，以确保在极端敌对条件下支付渠道交易的可用性和服务质量。此外，作为该项目的一部分，多机构和跨国私人投资机构团队正在部署新的私人区块链交易检索解决方案的分布式实例化，该解决方案将向公众开放使用。除了培养研究生，该项目还将重点放在本科生参与这一新兴的区块链研究领域。

This research explores ways to simultaneously improve both the scalability and privacy of blockchain technologies. A blockchain is a massively distributed, append-only log of transactions that is cryptographically protected from tampering. Thanks to their capacity towards facilitating fast and inexpensive transactions across the globe and their powerful scripting-language support for complex financial instruments, blockchains have already proven to be a highly disruptive force in the finance and e-commerce sectors. Nevertheless, at least two major hurdles still stand in the way of mainstream blockchain acceptance: 1) 'traditional' blockchain architectures are not sufficiently scalable to handle the ever-growing base of blockchain users and the resulting proliferation of transactions, and 2) despite myriad efforts to improve blockchain privacy, users of public blockchains remain susceptible to devastating attacks on the privacy of their accounts and transactions, which often lead to security breaches causing financial losses for the victims. The approaches explored in this project provide privacy for blockchain users where previous efforts have failed by rethinking the one-size-fits-all approach of using Tor to solve all problems requiring anonymity and/or unlinkability. Indeed, running complex protocols over Tor is fraught with risks and can open users to subtle-yet-devastating deanonymization attacks; the tailor-made solutions developed in this project leverage domain-specific knowledge to mitigate these risks.The project addresses privacy concerns as they relate both to traditional blockchain transactions and to newer 'payment channel network' transactions. Payment channel networks promise greatly improved scalability by allowing secure (off-chain) payment requiring no interaction with the blockchain ledger. In the context of traditional blockchain transactions, this research develops innovative ways to 1) privately publish transactions to a blockchain by integrating tailor-made anonymous communication protocols directly into the blockchain communication infrastructure, and 2) privately retrieve transactions from a blockchain using carefully optimized private information retrieval (PIR) protocols that support expressive blockchain queries. In the context of payment channel networks, the project 1) explores the (im)possibility of performing off-chain transactions privately, and 2) develops a new theoretical framework and toolkit of algorithms for ensuring availability and quality of service for payment channel transactions in extreme adversarial conditions. Additionally, as part of this project, the multi-institution and transnational team of PIs are deploying a distributed instantiation of the new private blockchain transaction retrieval solutions, which will be open to use by the public. Along with training graduate students, the project puts a major emphasis on undergraduate involvement in this emerging area of blockchain research.