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Circumventing Censorship

The Psiphon network frustrates censors by using trusted friends.
December 19, 2007

As Internet censorship continues in countries such as China and Burma, efforts to circumvent it are growing more sophisticated. (See “Burma’s Internet Crackdown.”) Researchers at the Citizen Lab at the University of Toronto are adding new capabilities to one such project, called Psiphon, in hopes of expanding its reach in censored countries.

Trusted social networks: Psiphon, a censorship-circumvention system, allows users to access censored sites through connections to trusted friends. The project’s logo, above, depicts the nodes that are the key to the system.

Ronald Deibert, director of the Citizen Lab, explains that Psiphon relies on trusted social networks to help users circumvent censorship. “It’s not so much about technology as it is about people determining what’s going on and responding in an intelligent way,” he says.

The original version, launched in December 2006, calls for people in uncensored countries to host proxy servers for people in censored countries. Because the censored user’s personal safety may be on the line, Deibert says, the researchers suggest that she connect only with people she knows and trusts. By downloading open-source Psiphon software, the uncensored user sets up a node that the censored user can access. Psiphon is designed to resemble the use pattern of a standard banking transaction, says Michael Hull, Psiphon’s lead software engineer. As long as the user accesses Psiphon sparingly, and when she really needs it, this should not create any unusual patterns that censors might notice. Because each of the Psiphon nodes is a small, private network that is disconnected from the others, they’re hard for censors to find and block. In addition, if censors block one node, that has no effect on the others.

The problem, says Hull, is that “there’s still that Achilles’ heel of someone living in a censored regime needing to know someone who lives in [a place like] Boston.” To solve this, the Citizen Lab group is building the Psiphon Web service, which allows users in censored countries to host Psiphon nodes without having to download software. (A downloaded program could put these people at risk by providing evidence of censorship circumvention on their hard drives.) “We want to empower people who live in censored countries to host their own servers,” Hull says.


  • See someone in Iran use Psiphon.

The Open Net Initiative, which researches Internet censorship worldwide, has identified pervasive filtering in countries including Burma, Iran, China, and Vietnam. (See “Internet Increasingly Censored.”) And censorship can go far beyond blocking obvious signs of dissent: one video made in Iran shows a person trying to use Google to search for “women’s studies” and finding that the search results are forbidden.

Ross Anderson, a professor of security engineering at the University of Cambridge, says that Internet censorship is part of a long tradition of government attempts to control communications. While it’s difficult to successfully censor the Internet, Anderson says, governments try anyway, blocking content from the average user. “Against people who really know what they’re doing, you don’t have much chance,” he says. “But many governments take the pragmatic view that if they can stop mass access to subversive stuff, that’s worth doing.” Effective censorship is a multilevel process, and, he adds, in oppressive regimes, they back it up with policemen. “If you use the obvious technical mechanisms to defeat, say, the Great Firewall of China, and they get to know about this, then they’ll send guys to knock on your door,” Anderson says.

Psiphon’s Web service attempts to shield users by keeping nodes disconnected. Although access to Psiphon’s main site is often blocked in censored areas, the researchers are working to get some initial Psiphon accounts set up in those countries through organizations and word of mouth. Once a user signs up for an account with Psiphon, the service provides him with access to a unique IP address in an uncensored country through which he can access Psiphon. The process is similar to that used by Geocities or Blogger, which allow people to run a website without running a server. Users identified as trustworthy (based on their using the service for a certain period of time without suspicious behavior, as well as on the researchers’ judgment) are given additional privileges, such as “power user” status, which allows them to invite others to share the node. Deibert says that he assumes some of these people will be adversaries seeking to block Psiphon. “We treat the nodes like pawns in a shell game,” he says. If a node becomes blocked in one country, the researchers can shift it to another country where it is not blocked. Much of the power of Psiphon relies on how cheap Internet hosting has become, Deibert says, and on the sheer number of nodes the project can host as a result.

Psiphon’s model is different from that of anonymizers such as the Tor Project, which can be used in some cases for censorship circumvention. The Tor Project allows a user to surf the Internet anonymously by passing her through so many nodes that an observer becomes unable to sort out the user’s actual traffic pattern. Anderson says that many times people can use the Tor Project to circumvent censorship by hiding their traffic within the flood of traffic to porn sites that also flows through Tor. “For many purposes, tools that are very widely used are best,” he says. “For other purposes, tools that are more personal, like Psiphon, are best.” In the case of severe government crackdown, he explains, it’s easy to block all Tor nodes. In a case such as that, he adds, the small, scattered Psiphon nodes would allow continued circumvention. “It’s not on the sort of scale where it becomes worth the effort of a large bureaucratic department of the people’s security police to identify my machine and blacklist it,” he says.

Deibert is glad for the presence of alternative methods. “Tor and Psiphon aren’t competing projects,” he says. “The more projects out there, the better.” Citizen Lab researchers are now working to carefully spread the word in censored countries about the new Psiphon Web service.

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