Psiphon – Bypass Content-Filtering Systems

Psiphon is a web proxy designed to help Internet users securely bypass the content-filtering systems used to censor the internet. Psiphon was developed by the Citizen Lab at the University of Toronto, building upon previous generations of web proxy software systems, such as the “SafeWeb” and “Anonymizer” systems.

In 2008 Psiphon was spun off as a Canadian corporation that continues to develop advanced censorship circumvention systems and technologies. Psiphon maintains its research and development lab and computer network “red team” at The Citizen Lab, Munk Centre for International Studies, University of Toronto.

There are currently two branches of Psiphon development: psiphon open source, and a commercial version that includes the managed proxy cloud and proprietary anti-counter circumvention system.

Psiphon open-source’s recommended use is among private, trusted relationships that span censored and uncensored locations (such as those that exist among friends and family members, for example) rather than as an open public proxy. Traffic between clients and servers in the Psiphon system is encrypted using the https protocol. Released under the GNU General Public License, Psiphon open-source is free software.

Psiphon open source is an internet proxy, described as “… a censorship circumvention solution that allows users to access blocked sites in countries where the Internet is censored” such as Australia. The psiphon software “…turns a regular home computer into a personal, encrypted server capable of retrieving and displaying web pages anywhere.” Psiphon was originally implemented in Python, but has been re-designed and re-written in C++, and designed as a cross-platform (Windows and Linux versions are currently available), user friendly proxy server tool which uses a https protocol to transfer data.

With a user name and password, people in countries that use Internet content filtering can send encrypted requests for information to a trusted computer located in another country and receive encrypted information in return. As https protocol is widely used for secure communication over the Internet (from web mail to Internet banking), no government can block https traffic without further restricting its citizens’ ability to use the web, something that has not dissuaded these governments’ Internet censorship efforts thus far.

According to Nart Villeneuve, Chief Technology Officer of Psiphon inc, “The idea is to get them to install this on their computer, and then deliver the location of that circumventor, to people in filtered countries by the means they know to be the most secure. What we’re trying to build is a network of trust among people who know each other, rather than a large tech network that people can just tap into.”

Psiphon takes a substantially different approach to censorship circumvention than other tools used for such purposes, such as The Onion Router aka Tor. Psiphon requires no download on the client side, and thus offers ease-of-use for the end user. But unlike Tor, psiphon is not an anonymizer, as the server logs all of the clients surfing history. Psiphon differs from previous approaches in that the users themselves have access to server software.

The developers of Psiphon have provided the user with a Microsoft Windows platform executable for the Psiphon server. If the server software attains a high level of use this would result in a greater number of servers being online. A great number of servers online would make the task of attacking the overall user base more difficult for those hostile to use of the psiphon proxy than attacking a few centralized servers, because each individual web proxy would have to be disabled one by one.

In the most recent edition of the software, the psiphonode pings the Citizen Lab to “check in” and returns your public IP, which is then distributed to users. Although this does create the theoretical danger of a canonical list of psiphonodes which could be a target for an adversary determined to block psiphon, the Citizen Lab does not archive this information as a matter of policy. Additionally, users have the option to configure their psiphonodes not to “check in” with the Citizen Lab.

Through the psiphon control panel, psiphonode administrators have access to a log of sites that their psiphonites access, which makes the psiphon user subject to the consequences of any lack of good security practices, ill will, or possible censorship by the psiphonenode administrator. The authors of psiphon stress that these issues are “trust” issues, with exception of poor security practices, and should not present a problem because of the positive social relationship(s) between psiphon user(s) and psiphonode administrator(s).

The theory being that if there is a good enough relationship to establish a psiphon user to psiphonode administrator tie, issues such as psiphonode censorship and ill will are not likely to arise, hence the term “social networks of trust” used in psiphon literature.