The "Great Firewall of China," used by the government of the People's Republic of China to block users from reaching content it finds objectionable, is actually a "panopticon" that encourages self-censorship through the perception that users are being watched, rather than a true firewall, according to researchers at UC Davis and the University of New Mexico.

The researchers are developing an automated tool, called ConceptDoppler, to act as a weather report on changes in Internet censorship in China. ConceptDoppler uses mathematical techniques to cluster words by meaning and identify keywords that are likely to be blacklisted.

Many countries carry out some form of Internet censorship, said UC Davis in a release. Most rely on systems that block specific Web sites or Web addresses, according to Earl Barr, a graduate student in computer science at UC Davis who is an author on the paper. China takes a different approach by filtering Web content for specific keywords and selectively blocking Web pages.

In 2006, a team at the University of Cambridge, England, discovered that when the Chinese system detects a banned word in data traveling across the network, it sends a series of three "reset" commands to both the source and the destination. These "resets" effectively break the connection. But they also allow researchers to test words and see which ones are censored. Barr, along with Jed Crandall, a recent UC Davis graduate who is now an assistant professor of computer science at the School of Engineering, University of New Mexico; UC Davis graduate students Daniel Zinn and Michael Byrd; and independent researcher Rich East sent messages to Internet addresses within China containing a variety of different words that might be subject to censorship.

If China's censorship system were a true firewall, most blocking would take place at the border with the rest of the Internet, Barr said. But the researchers found that some messages passed through several routers before being blocked.

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