Now that it's getting in the way of the Olympics coverage, everyone in the world is getting indignant over the Great Firewall of China. Stilgherrian gives a guided tour.

China’s “Great Firewall” (GFW), officially the Golden Shield Project of the Ministry of Public Security, is both clever and stupid, subtle and blunt.

As with any internet filtering system, there are only two methods to block bad stuff: keep a list of “bad sites” and prevent access, or look at the content live and figure out whether it’s good or bad on the fly. The GFW uses both.

Al Gore was mocked for calling the internet the “Information Superhighway”, but the analogy works. Like the road network, a maze of suburban streets leads to relatively few freeways, all administered by a myriad of local authorities.

When your computer requests a website, imagine a truck driving out your front gate. The driver knows the site’s name but not how to get there. Normally, you’ll get directions.

“Amnesty International? Sure, that’s 78.136.0.19,” says the domain name system (DNS).

“78.136.0.19? Go via Telstra, ask again once you’re in San Jose,” says your ISP’s router. In San Jose, you’re told to go to New York and so on to Amnesty’s London office.

In China, though, your driver only gets blank looks.

“Amnesty? Never heard of it.”

“78.136.0.19? No, no such place.”

With relatively few links connecting China to the world, this block is easy. Unlike Senator Conroy’s p-rn filters, the GFW doesn’t have to worry about collateral damage. It blindly blocks entire sites, as well every site sharing the same internet address — not only Amnesty, but everyone in that office tower.

The GFW also looks at content, and here’s the true subtlety. Researchers at the ConceptDoppler project have found that it can disrupt internet traffic within China that even mentions touchy subjects. Imagine your truck encountering random checkpoints. If it contains banned concepts like “news blackout” or “gerontocracy” your delivery is simply burned, never to be seen again.

ConceptDoppler says the banned words still get through 28% of the time, and the blocking can’t keep up with heavy internet traffic. But even partial blocking encourages self-censorship through the perception that you’re being watched. Perhaps that’s even more effective because it discourages offline conversation too.

Getting around the GFW is easy enough for geeks — though perhaps beyond the skills of average internet users like sports journalists. Wikipedia lists the techniques, and Reporters Without Borders has a handbook.

Using proxies is like first sending your truck to a benign destination so it gets those helpful directions. Once there, the package is opened and the secret instructions inside forward your message to the real destination. To avoid content filtering, just speak in code. Learn to say “duck-breeding club” rather than “student dissident meeting”.

Stilgherrian

The Great Firewall of China: how it works, how to bypass it