 A growing number of software tools are available that provide some form of privacy (usually anonymity) for their users, such tools are commonly known as privacy enhancing technologies (Danezis &amp; Gürses 2010, Other Internet Resources). Examples include communication-anonymizing tools such as Tor (Dingledine, Mathewson, &amp; Syverson 2004) and Freenet (Clarke et al. 2001), and identity-management systems for which many commercial software packages exist (see below). Communication anonymizing tools allow users to anonymously browse the web (with Tor) or anonymously share content (Freenet). They employ a number of cryptographic techniques and security protocols in order to ensure their goal of anonymous communication. Both systems use the property that numerous users use the system at the same time which provides k-anonymity (Sweeney 2002): no individual can be uniquely distinguished from a group of size k, for large values for k. Depending on the system, the value of k can vary between a few hundred to hundreds of thousands. In Tor, messages are encrypted and routed along numerous different computers, thereby obscuring the original sender of the message (and thus providing anonymity). Similarly, in Freenet content is stored in encrypted form from all users of the system. Since users themselves do not have the necessary decryption keys, they do not know what kind of content is stored, by the system, on their own computer. This provides plausible deniability and privacy. The system can at any time retrieve the encrypted content and send it to different Freenet users.