Network sniffers really get up your nose

Stephen Hutcheon
August 1, 2008

WITH 253 million people online, China now has the most internet users of any country.

Beijing employs a vast bureaucracy of censors and a phalanx of technically advanced filters to police how its citizens use the internet.

The Great Firewall of China - or the Golden Shield Project, as it is officially known - is meant to prevent internet users from reading or publishing reports that criticise the Government.

The task is made easier because almost all internet traffic between China and the outside world comes through a few gateways at one of three points near the cities of Beijing, Shanghai, and in the south, Guangzhou.

The filters work in much the same way as home filters that stop children from accessing inappropriate websites.

Content filtering technologies primarily rely on lists of banned sites identified by their unique internet protocol (IP) addresses.

In addition, Chinese authorities use keyword-matching tools, which can identify suspect words or phrases.

This allows censors to take out websites that may not yet have made it on to an official list of banned sites.

An American author who wrote at great length about the Golden Shield in The Atlantic Monthly in February, James Fallows, said the Chinese have also installed a device called a "tapper", or "network sniffer", which copies every skerrick of data that comes in through these gateways and shunts that through the surveillance computers for inspection.

Although this happens in a split second, it accounts

for some of the slow speeds that internet users experience in China.

If the data fails to pass muster, the censor's computer interrupts the process of connecting the user's computer to the website, resulting in what is known as a 404 error: "site not found".