CIO —
A group of researchers at the University of Cambridge claims to have found a way to circumvent China’s Internet content controls, but some doubt whether their findings really offer a breakthrough.
Their paper, titled "Ignoring the Great Firewall of China," offers an insight into the workings of China’s complex filtering system, which Chinese officials rarely discuss in public. The paper was written by Richard Clayton, Steven Murdoch and Robert Watson of Cambridge’s Computer Laboratory.
The Chinese government filters content by looking for banned keywords contained in packets being transmitted over the Internet. Thus, a computer requesting a webpage that contains the word "falun," a reference to a banned spiritual group, will be blocked from accessing the webpage, the researchers said.
The filtering is done using routers and intrusion-detection technology, the paper said. When a banned keyword is detected, the router sends reset connection (RST) packets to both the client computer and the Web server, prompting them to break their connection and block the user’s access to the site.
RST is one of six flags, or control bits, used to define the purpose of a packet sent using transfer control protocol (TCP), which allows computers to connect over a network. When a computer receives an RST packet, it breaks off the connection.
Once the connection is broken, the Great Firewall’s routers continue to block all connections between the two computers for a period of time using RST packets. The length of time varied, ranging from a few minutes to nearly an hour, the researchers said, putting the average at about 20 minutes.
The disclosures in the paper offered nothing new for those familiar with how the filtering system works. "There’s nothing in there I didn’t know two years ago," said Michael Robinson, an information technology expert in Beijing.
He questioned whether the paper’s findings make any difference. "The connection reset system described in the paper is only one layer of a much larger multilayer content control system. Using encrypted proxy servers is the only way around all of them," he said.
In their paper, the researchers proposed using special software or modifications to firewall software that would ignore RST packets to circumvent the Great Firewall. Robinson questioned whether this method offered an improvement over the use of proxy servers, which are commonly used by Chinese Internet users to skirt government controls.
"Any solution to the connection reset problem would involve just as much work for individual Chinese Internet users as it does to set up a proxy connection, and the proxies provide a complete solution, rather than a partial solution as described in the paper," he said.
