Mix network

A mix network is a routing protocol that makes communications hard to trace by sending messages through a chain of proxy servers called mixes. Each mix takes in messages from many senders, shuffles them and sends them on in random order to the next destination, which may be another mix, so the link between the source of a request and its destination is broken. A message is encrypted for every mix in turn with public key cryptography, layered like nested dolls of equal size, and each mix strips off only its own layer to learn where to send the message next, so a mix knows only the node it received the message from and the node it passes it to. Untraceability can survive even when all but one of the mixes are compromised, against some weaker adversaries. David Chaum is credited with first describing the idea in 1981, and his master's thesis paper published it in 1979. Anonymous remailers such as Mixmaster, onion routing and systems including Tor, I2P and Freenet build on the concept.