Communication networks are comprised of nodes. Those nodes are normally thought of as computers used and operated by institutions or natural persons; we suppose this here. Through the means of the network the nodes exchange information with each other. It is always possible for a third party to identify the nodes and thereyby the instituions and persons involved in a particular information exchange. Such a third party uses the meta-information generated by the information exchange in the network; such meta-information which reveals information about the participating nodes is inevitably needed for an efficiently operating communication network. The actual information that is exchanged can be protected by crytographic techniques. One way to protect the identity of the participating nodes is through anonymous overlay networks which make the generated meta-information useless for third parties.

An overlay networks is an additional layer on top of an high-level network like the Internet that adds additional functionality. Normally only part of the nodes participate in such an overlay network; most times it is implemented by certain software modules that add virtual network interfaces to the operating systems of the participating nodes.

Anonymous overlay networks are networks that route the information exchange through the participating nodes in a way that cannot or is hard to reconstrunct by a third party. This means that they deviate from the optimal route which leads to the fact that there is a tradeoff between anonymity and performance. Like in the real world the more nodes participate in an anonymous overlay network the more anonymity a node of this network gets. There are several concepts for implementing such a network and all of them do only give a certain degree of anonymity.

Underlying anonymity network

OnionCoffee implements the protocols of the anonymous overlay network TOR. The TOR network is an anonymous overlay network for the Internet. It is currently widely deployed which was one of the reasons for choosing it in the first place. Applications that use OnionCoffee can utilize an already existing anonymous network infrastructure. OnionCoffee works currently only as a client for the TOR network. Server functionality is in an experimental stadium.