Updated 26 May, 2012, 4:18 pm IST

Anonymizing the Net: The Onion Router

12 Oct, 2006, 6:04 pm IST | by Aalaap Ghag

The Onion Router (TOR) is a specialized network of anonymous routers that protect your privacy while using the Internet.

What is Tor?

Tor, or 'The Onion Router', is a peer to peer network of specialized nodes that randomize the hop sequence so connections in the same session may take a completely different route to reach the destination. As a result, the IP address reported to the destination website is random everytime the connection is made, making it difficult to trace the route. Connections between nodes and routers are also encrypted with multiple layers, which is what puts the "onion" in the name. The Tor routers also don't store any logs of IP addresses that come and go through them, further enhancing your privacy.

This picture shows a typical Tor network flow. Light green routers are available Tor routers. The amber node is the source, this time using the Tor software, and the green node is the destination which doesn't need to be running Tor software, as the connection is converted into a normal one from the last Tor node. The green line indicates an encrypted line of communication between the Tor routers. Notice the relatively random sequence of hops taken by the Tor flow.

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When a connection is initiated with the Tor network, a list of available routers is procured and one of them is chosen to carry the connection forward. The chosen router then looks for another random router in the vicinity and forwards the data to it. This continues till the connection reaches the closest router, from where it breaks out of the Tor network into the regular internet to access the destination website. Since the connection can come from any of the various Tor routers without any information of the actual source, the destination has random source IP addresses in the logs, completely anonymizing your browsing session.

.onion Websites

Tor is not only a network of routers and proxy servers. It is also possible to host "hidden" websites within the Tor network itself, which get a pseudonymous TLD ".onion". They are virtual domains that don't actually exist in the public internet and also cannot be accessed by computers that are not running the Tor software. Sites get random names using public keys, such as 6sxoyfb3h2nvok2d.onion, making them even more difficult to identify.

How to use Tor

There are two components that form the Tor network: the Tor server/router and the Tor client. Routers are generally dedicated machines that are kept for forwarding and bouncing traffic around the network. Clients are installed by peers wanting to anonymize their browsing session. A typical end user simply downloads and installs the Tor client and configures his applications (browser, instant messenger, etc.) to access the internet via the Tor client, which runs as a SOCKS proxy on the user's computer.

If this sounds like a lot of work, then there are bundled solutions that work out-of-the box, such as Torpark and Operator, which are versions of Firefox and Opera pre-bundled with Tor software. Torpark is new and easiest to use, which is why we'll be reviewing that for you next.

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