Knocking Holes in China’s ‘Great Firewall’
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Written By Reprise Media | June 28, 2006 | Share This
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“Ignore it and it’ll go away” is the kind of motherly advice that seldom seems to work - but it might just be one way ordinary users can bypass China’s much-discussed web censorship apparatus.
Techdirt points to a blog post by Richard Clayton, a security researcher at Cambridge University, that examines the ‘Great Firewall’ and finds parts of it to be surprisingly flimsy. While the Chinese government makes sure that “some sites are blocked unconditionally,” they rely mostly on a less hardy system to keep much of the content they find objectionable from reaching their citizens.
When one of their web filters detects a prohibited term, it does “not actually prevent the packet containing the keyword from passing through the main router,” since that would make everything a lot slower and a lot more complicated. Instead, filtering machines send ‘reset’ requests to both ends of the connection, which are assumed to be legitimate. Even though the material passes through the router, the local computers never see it.
However, “if both of the endpoints were to completely ignore the firewall’s reset packets, then the connection will proceed unhindered!” That result is easy to get by “applying simple firewall rules,” says Clayton, who’s experimented with the solution and exclaims, “It works just fine!” He, Steven Murdoch and Robert Watson have prepared an academic paper (.pdf) on the subject that they’ll present at a Cambridge workshop this week.
Techdirt links to more commentary from Ed Felten, who writes that this Chinese ‘firewall-lite’ might be violating US law in specific circumstances, as it essentially amounts to a deliberate denial-of-service attack on the end points of any given connection. No skin off China’s back, but it could put China’s US suppliers in hot water.
Topics: Technology |
Bypass Firewalls
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