The importance of safeguarding individuals’ privacy rights in online activities is unmistakable in today’s anonymity networks. Since the introduction of Mixnet by Chaum, numerous anonymity networks with different objectives and design principles have emerged, providing a diverse range of applications for privacy-conscious users. However, security issues in anonymity networks have persistently existed and continue to impact their survival and development. Each anonymity network presents distinct security challenges, making it more challenging for researchers to achieve a comprehensive and systematic understanding of their security. The current literature exhibits some unavoidable gaps, including the lack of vulnerability perspectives, a unified understanding of diverse attack types, defense perspectives, and theoretical perspectives. To address these gaps, we investigate prevailing attacks targeting anonymity networks from the viewpoint of network designers and operators. We use Tor, I2P, and Freenet (arguably the three most popular anonymity networks) as case studies. Starting with these attacks, we conduct an in-depth analysis of the vulnerabilities underlying them and explore related defense mechanisms and formal security. Specifically, we classify vulnerabilities into external and internal categories, utilizing the protocol stack of an anonymity network to guide the categorization of internal vulnerabilities. Furthermore, we examine their root causes. In addition to these aspects, we emphasize the importance of formal security in researching the security of anonymity networks by integrating the investigated vulnerabilities, attacks, and defenses. Through this comprehensive, thorough, and unified approach, this paper aims to provide insights into the security of anonymity networks and offer general research findings. Finally, we discuss ongoing challenges and future directions in this specific area.

中文翻译：

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匿名网络安全的系统调查：漏洞、攻击、防御和形式化


在当今的匿名网络中，保护个人在线活动隐私权的重要性是显而易见的。自从 Chaum 推出 Mixnet 以来，出现了众多具有不同目标和设计原则的匿名网络，为注重隐私的用户提供了多样化的应用程序。然而，匿名网络的安全问题始终存在，并持续影响其生存和发展。每个匿名网络都面临着不同的安全挑战，这使得研究人员更难以全面、系统地了解其安全性。目前的文献存在一些不可避免的差距，包括缺乏脆弱性视角、对不同攻击类型的统一理解、防御视角和理论视角。为了解决这些差距，我们从网络设计者和运营商的角度调查了针对匿名网络的普遍攻击。我们使用 Tor、I2P 和 Freenet（可以说是三个最流行的匿名网络）作为案例研究。我们从这些攻击入手，深入分析其背后的漏洞，探索相关的防御机制和形式安全。具体来说，我们将漏洞分为外部和内部两类，利用匿名网络的协议栈来指导内部漏洞的分类。此外，我们还研究了其根本原因。除了这些方面之外，我们还通过整合所调查的漏洞、攻击和防御来强调形式安全在研究匿名网络安全方面的重要性。 通过这种全面、彻底和统一的方法，本文旨在提供对匿名网络安全性的见解并提供一般性研究成果。最后，我们讨论该特定领域当前的挑战和未来的方向。