How to Find Hidden Users: A Survey of Attacks on Anonymity Networks

Communication privacy has been a growing concern, particularly with the Internet becoming a major hub of our daily interactions. Revelations of government tracking and corporate profiling have resulted in increasing interest in anonymous communication mechanisms. Several systems have been developed with the aim of preserving communication privacy via unlinkability within a public network environment such as Tor and I2P. As the anonymity networks cannot guarantee perfect anonymity, it is important for users to understand the risks they might face when utilizing such technologies. In this paper, we discuss potential attacks on the anonymity networks that can compromise user identities and communication links. We also summarize protection mechanisms against such attacks. Many attacks against anonymity networks are well studied, and most of the modern systems have built-in mechanisms to prevent these attacks. Additionally, some of the attacks require considerable resources to be effective and hence are very unlikely to succeed against modern anonymity networks.