Internet users in China will soon be able to circumvent the Great Firewall and access any of the 3,000 blocked sites in the country, thanks to new plug-in developed by researchers at the University of Massachusetts, Amherst.

The circumvention system, called CacheBrowser, exploits the difficulty Internet censors have in blocking content from a content delivery network (CDN). A CDN is a system of servers that deliver Web content to a user based on their geographic location, the origin of the webpage, and a content delivery server.

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"Blocking CDN content poses unique technical and non-technical challenges to the censors," the researchers said. "CacheBrowser's superior quality-of- service is thanks to its publisher-centric approach, which retrieves blocked content directly from content publishers with no use of third-party proxies."

CacheBrowser evades censors' DNS interference by directly retrieving blocked content from one of the tens of thousands of CDN servers hosting the same blocked CDN content. The researchers were able to use the client-side software to get around the Great Fire Wall and access outlawed websites like Facebook.com or Change.org.

According to the report, the practice of caching Internet content, which is intended to improve performance, security, and reliability, has "revolutionized" the way Internet content is being delivered. And it also makes it difficult to censor.

"Content caching by CDN networks poses significant technical and non-technical challenges to the censors, even despite self-censorship by a major CDN provider," said the report. "We show that IP address blocking, a highly-effective technique in blocking regular Internet content, is impractical in blocking CDN content, and that the [Great Firewall] refrains from IP blocking CDN content due to the potential collateral damage."

 This is because CDN content is typically hosted on several thousand IP addresses that are shared among tens of thousands of non-related content publishers. As a result, any attempt to block an IP address to censor content will also censor the non-related publishers that might not be forbidden in the country.

The plugin is able to avoid DNS interference by directly retrieving blocked CDN content from one of the tens of thousands of CDN servers hosting the same blocked CDN content.

Unlike circumvention systems that are proxy-based, such as Tor and Psiphon, CacheBrowser takes a new circumvention approach, which the researchers refer to as "publisher-centric." Under this approach, users elude third-party proxies to obtain censored Internet content, but retrieve the censored content directly from the publishers.

"We show that CacheBrowser's publisher-centric approach has significant advantages over traditional proxy-based circumvention systems," said the report.

TagsCracks Form in China’s Great Firewall As Plugin Skirts Censorship, CacheBrowser, content delivery network, CDN, DNS interference, Tor, Psiphon, University of Massachusetts Amherst, blocked sites, Great Firewall, Great Fire Wall