Tor (anonymity network)

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Tor

Developer(s)	The Tor Project
Initial release	20 September 2002 (2002-09-20)
Stable release	0.2.1.30 (23 February 2011; 2 months ago (2011-02-23))
Preview release	0.2.2.25-alpha (29 April 2011; 19 days ago (2011-04-29))
Written in	C
Operating system	Cross-platform
Type	Onion routing, Anonymity
License	BSD license
Website	www.torproject.org

Tor is a system intended to enable online anonymity, composed of client software and a network of servers which can hide information about users' locations and other factors which might identify them. Use of this system makes it more difficult to trace internet traffic to the user, including visits to Web sites, online posts, instant messages, and other communication forms. It is intended to protect users' personal freedom, privacy, and ability to conduct confidential business, by keeping their internet activities from being monitored. In March 2011 The Tor Project was awarded the Free Software Foundation's 2010 Award for Projects of Social Benefit on the following grounds: "Using free software, Tor has enabled roughly 36 million people around the world to experience freedom of access and expression on the Internet while keeping them in control of their privacy and anonymity. Its network has proved pivotal in dissident movements in both Iran and more recently Egypt." The software is open-source and the network is free of charge to use.

Though the name Tor originated as an acronym of The Onion Routing project, the current project no longer considers the name to be an acronym, and therefore does not use capital letters.

Tor is an implementation of onion routing: The service works by relaying communications through a network of systems run by volunteers in various locations. Because the internet address of the sender and the recipient are not both readable at any step along the way (and in intermediate links in the chain, neither piece of information is readable), someone engaging in network traffic analysis and surveillance at any point along the line cannot directly identify which end system is communicating with which other. Furthermore, the recipient knows only the address of the last intermediate machine, not the sender. By keeping some of the network entry points hidden, Tor is also able to evade many internet censorship systems, even ones specifically targeting Tor.

1 History
2 Operation
- 2.1 Originating traffic
- 2.2 Hidden services
3 Weaknesses
4 Legal aspects
5 Implementation
6 See also
7 Footnotes
8 References
9 Further reading
10 External links

History

An alpha version of the software, with the onion routing network "functional and deployed", was announced on 20 September 2002. Roger Dingledine, Nick Mathewson, and Paul Syverson presented "Tor: The Second-Generation Onion Router" at the 13th USENIX Security Symposium on 13 August 2004.

Originally sponsored by the US Naval Research Laboratory, Tor was financially supported by the Electronic Frontier Foundation from 2004 to 2005. Tor software is now developed by the Tor Project, which since December 2006 is a 501(c)(3) research/education nonprofit organization based in the United States of America that receives a diverse base of financial support.

Operation

Tor aims to conceal its users' identity and their network activity from surveillance and traffic analysis. Volunteers operate an overlay network of onion routers that employ encryption in a multi-layered manner (hence the onion routing metaphor) to ensure perfect forward secrecy between routers, thereby providing users with anonymity in network location. That anonymity extends to the operation of censorship-resistant servers via Tor's anonymous hidden service feature.

Originating traffic

Users of a Tor network run an onion proxy on their machine. The Tor software periodically negotiates a virtual circuit through the Tor network, using multi-layer encryption, ensuring perfect forward secrecy. At the same time, the onion proxy sof

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