Onion routing

Onion routing is a technique for anonymous communication over a computer network. In an onion network, messages are encapsulated in layers of encryption, analogous to layers of an onion. The encrypted data is transmitted through a series of network nodes called onion routers, each of which "peels" away a single layer, uncovering the data's next destination. When the final layer is decrypted, the message arrives at its destination. The sender remains anonymous because each intermediary knows only the location of the immediately preceding and following nodes.

Onion routing was developed in the mid-1990s at the U.S. Naval Research Laboratory by employees Paul Syverson, Michael G. Reed, and David Goldschlag to protect U.S. intelligence communications online. It was further developed by the Defense Advanced Research Projects Agency (DARPA) and patented by the Navy in 1998.

Computer scientists Roger Dingledine and Nick Mathewson joined Syverson in 2002 to develop what would become the largest and best known implementation of onion routing, Tor, then called The Onion Routing project or TOR project. After the Naval Research Laboratory released the code for Tor under a free license, Dingledine, Mathewson and five others founded The Tor Project as a non-profit organization in 2006, with the financial support of the Electronic Frontier Foundation and several other organizations.

An onion is the data structure formed by "wrapping" a message with successive layers of encryption to be decrypted ("peeled" or "unwrapped") by as many intermediary computers as there are layers before arriving at its destination. The original message remains hidden as it is transferred from one node to the next, and no intermediary knows both the origin and final destination of the data, allowing the sender to remain anonymous.

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