Onion routing

Onion routing is a method of sending encrypted messages using various proxies (“onion routers”) and only supplying limited information to each proxy. This method is useful when the security of each proxy is questionable or to confuse the link between the sender and the recipient.

The message is wrapped in layers of encryption and each proxy strips a layer away after receipt to determine the next address to send the message. The result is that while each proxy knows where the message came from and where it was going, no one proxy has information about the original sender or ultimate destination and may only have information on one step in a very long chain. Outside parties with the ability to monitor all the proxies may still be able to determine the original sender and intended recipient, especially if the person monitoring is able to employ timing analysis to compare the timing or incoming and outgoing messages to determine the email’s path. Timing analysis can be frustrated by buffering several messages before sending or bundling several messages together (“garlic routing”).