CIF: Medium: Anonymous Broadcasting over Networks: Fundamental Limits and Algorithms

在一个自由的社会里，人们有权在不受过度监视的情况下生活。当这项权利受到侵犯时，匿名保护技术可以提供一个安全网。匿名保护系统是专门为防止对手将用户与他们在系统内的行为联系起来而设计的；如今，大多数在线服务的设计都没有保护匿名性。本课题研究用户在网络上广播敏感信息的网络系统的匿名性。它考虑了两种代表性的应用：匿名微博和加密货币。匿名微博指的是用户在社交图谱上发布消息的社交网络；例如Yik Yak和Whisper。加密货币是分布式的数字货币，允许社区集体加密验证交易的合法性；比特币就是最成功的例子。匿名微博平台和加密货币都通过网络传播敏感信息，通常被认为是保护用户匿名的系统。该项目旨在从第一原则出发，了解现有广播协议对统计去匿名化攻击的漏洞，以及是否可以通过精心设计新协议来防止此类攻击。此外，该项目将开发开源实现来演示关键理论，包括分布式匿名消息传递应用程序和对比特币网络堆栈的轻量级升级。该项目还包括在这一重要研究领域培养研究生和本科生。该项目分三步进行。第一步是建立模型，提取出简单的、规范的数学模型，这些模型捕捉了这些复杂系统的本质。第二步是源检测，其中考虑对手执行统计推断来对广播源进行去匿名化，并使用第一步的数学模型来分析当前协议的漏洞。最后一步关注源隐藏，其目的是设计新颖的广播和网络管理协议，提供可证明的最佳匿名保证，同时保持目标应用程序的高实用性。

In a free society, people have the right to live without being unduly monitored or surveilled. When that right is violated, anonymity-preserving technologies can provide a safety net. Anonymity-preserving systems are specifically designed to prevent adversaries from linking users to their actions within the system; most online services today are not designed to protect anonymity.This project studies the anonymity properties of networked systems in which users broadcast sensitive information over a network. It considers two representative applications: anonymous microblogging and cryptocurrencies. Anonymous microblogging refers to social networks where users broadcast messages over a social graph; examples include Yik Yak and Whisper. Cryptocurrencies are distributed, digital currencies that allow a community to collectively, cryptographically verify the legitimacy of transactions; Bitcoin is the most successful example. Both anonymous microblogging platforms and cryptocurrencies broadcast sensitive messages over a network and are generally perceived as systems that protect user anonymity. This project aims to understand, from first principles, the vulnerabilities of existing broadcasting protocols against statistical deanonymization attacks, and whether such attacks can be prevented by carefully designing new protocols. Additionally, the project will develop open-source implementations to demonstrate the key theory including a distributed anonymous messaging application and a lightweight upgrade to Bitcoin's networking stack. The project also includes training of graduate and undergraduate students in this important research area.The project is conducted in three steps. The first step is model-building which extracts simple, canonical mathematical models that capture the essence of these complex systems. The second step is source detection, where an adversary performing statistical inference to deanonymize the source of a broadcast is considered, and the mathematical models from step 1 are used to analyze the vulnerability of current protocols. The final step focuses on source hiding where the aim is to design novel broadcasting and network-management protocols that give provably-optimal anonymity guarantees while maintaining high utility for the target applications.