Tor is the most popular volunteer-based anonymity network with over 2 million daily users, more than 6,000 active servers & around 110,000 hidden services.
Tor is a low-latency anonymity network based on the ideas of onion routing and telescoping. Clients have anonymous communication to a server by proxying their traffic through a chain of three Tor relays. Specifically, prior to sending the data, a client chooses three Tor relays and uses public key cryptography to negotiate symmetric session keys with them, establishing a circuit. Whenever a client wants to send a piece of data he packs it into Tor cells and encrypts them with multiple layers of encryption using the session keys. As the cells travel along the circuit, each relay strips off one layer of encryption. Hence the server receives the original piece of data while each relay along the path knows only which relay it received the Tor cell from and which relay it forwarded the cell to.
The Onion Router (TOR)
TOR is free and open-source software for enabling anonymous communication. The name is derived from an acronym for the original software project name “The Onion Router”. Tor directs Internet traffic through a free, worldwide, volunteer overlay network consisting of more than seven thousand relays to conceal a user’s location and usage from anyone conducting network surveillance or traffic analysis. Using Tor makes it more difficult to trace Internet activity to the user: this includes “visits to Web sites, online posts, instant messages, and other communication forms” Tor’s intended use is to protect the personal privacy of its users, as well as their freedom and ability to conduct confidential communication by keeping their Internet activities from being monitored.
Tor Hidden Services
Tor Hidden Services are a feature which was introduced in 2004 to add responder anonymity to Tor. Specifically, hidden services allow running an Internet service (e.g. a Web site, SSH server, etc.) so that the clients of the service do not know its actual IP address. This is achieved by routing all communication between the client and the hidden service through a rendezvous point which connects anonymous circuits from the client and the server.
The Tor hidden service architecture is comprised of the
- Internet service which is available as Tor hidden services
- Client, which wants to access the Internet service
- Introduction points (IP): Tor relays chosen by the hidden service and which are used for forwarding management cells necessary to connect the Client and the hidden service at the Rendezvous point
TOR Project – The Creators
The Tor Project, Inc, became a 501(c)3 nonprofit in 2006, but the idea of “onion routing” began in the mid 1990s.
In the 1990s, the lack of security on the internet and its ability to be used for tracking and surveillance was becoming clear, and in 1995, David Goldschlag, Mike Reed, and Paul Syverson at the U.S. Naval Research Lab (NRL) asked themselves if there was a way to create internet connections that don’t reveal who is talking to whom, even to someone monitoring the network. Their answer was to create and deploy the first research designs and prototypes of onion routing.
The goal of onion routing was to have a way to use the internet with as much privacy as possible, and the idea was to route traffic through multiple servers and encrypt it each step of the way. This is still a simple explanation for how Tor works today.
In the early 2000s, Roger Dingledine, a recent Massachusetts Institute of Technology (MIT) graduate, began working on an NRL onion routing project with Paul Syverson. To distinguish this original work at NRL from other onion routing efforts that were starting to pop up elsewhere, Roger called the project Tor, which stood for The Onion Routing. Nick Mathewson, a classmate of Roger’s at MIT, joined the project soon after.