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.