David Chaum has introduced the two most prominent techniques to anonymise data communication. One bases on the solution to the Dining Cryptographers problem  and is often referred to as DC-nets, the other are mix-networks . Although DC-nets have information theoretic anonymity guarantees, they are not believed to be very useful to anonymise the communication in widely distributed networks. In this
paper, we will focus on mix-networks, as they are considered as the most promising approach to solve the problem of anonymous communication in the Internet. Several systems based on Chaum’s idea to provide anonymous access to Internet services have been operational. The Mixmaster system  enables users to send electronic mail anonymously. Variations to the basic mix design to support near-real-time
services such as web browsing have led to circuit-based systems: Onion Routing , Freedom , Web Mixes , and the Anonymity Network . All these systems consist of relatively few and well known mixes that are used by a much larger number of users. We therefore name this type of mix-networks static mix-networks. Recently, two further variations of the traditional mix-network approach have been proposed, Tarzan  and MorphMix . Both systems are peer-to-peer based in the sense that every
user is also a mix at the same time. Since the mixes in these systems can show up and disappear again at any time, we name this type dynamic mix-networks.