10.7. Onion Routing

One of the most successful anonymous routing tools is the Onion Routing protocol built by by Paul Syverson, David Goldschlag, Michael Reed, Roger Dingledine and Nick Mathewson. The protocol has been revised and extended since its introduction in 1996 and it is implemented by a rich collection of tools including a version of the Firefox browser.

The system can protect a user from an eavesdropper tracking their browsing by sending the requests through a series of randomly chosen proxy servers. Each link in the path is encrypted with a different layer of encryption a process that gives the protocol its name. Each proxy server along the chain will strip off its layer of encryption until the last proxy server will spit out an unencrypted packet of data to the eventual source. All of the proxy servers along the path can confound an eavesdropper by making it impossible to know which data is coming and which is going. Anyone watching a user may see only encrypted data leaving the machine and encrypted data returning effectively making it impossible to track where the packets go and who sends back a response.