July 1, 2006

Back in action + Secrets of the GFW revealed

Filed under: China,Great Firewall,Politics — ricecracker @ 9:14 am

Rice Cracker managed to get itself blocked by the Great Firewall after only its first breath outside the womb. Not sure why or how, but the problem’s been fixed with a move to a new IP address.

While it probably doesn’t clear up the Rice Cracker story, some good firewall-related news out of England: Researchers at Cambridge have reportedly discovered how China accomplishes automatic blocking of web pages that contain counterrevolutionary keywords. Andrew Lih, a new media researcher at the University of Hong Kong, explains it in lay terms:

…the simple explanation is that the GFW sends a “TCP reset” packet to both the web server supplying the suspicious page and to the client (ie. your computer) loading it. It’s the equivalent of an “emergency stop” packet usually reserved for situations of bad connectivity so that both sides know to disconnect abruptly.

Lih goes onto to marvel at the system’s simplicity:

GFW operators could use off-the shelf Cisco (or whatever) routers with no modified firmware whatsoever, and just have a set of machines sit on the side detecting keywords, and sending out “TCP resets.” Simple, effective, and with a low impact for network engineering.

This raises the interesting possiblity that Cisco’s claims it hasn’t actively colluded with the CCP in choking off Chinese people’s information supply might actually true. Or more true, at any rate. [Although it doesn't get them off the hook for reaping profits out of the whole odious operation.]
More importantly, the use of TCP reset packets means that banned information gets through into China, all the way to the front porch of your browser, before your computer slams the door in its face. The solution, at least in theory, is as simple as the problem: tell your computer to be more hospitable (i.e., ignore TCP reset orders). Lih points out a catch: Both Web servers and client must be programmed to do this, so builders of major operating systems would have to get on board. Mabye unlikely, but still, score one against bad guys.

The reasearchers–Richard Clayton, Steven Murdoch and Robert Watson–go into more detail on their own blog (with a downloadable PDF of their original report).