As far as I can tell, China doesn't "keyword-filter" in the sense most
people think of that phrase. That is, the Great Firewall isn't inspecting
all the text which flows through it, failing to deliver any web pages which
have offending words. The filtering is of two main types:
1) any of thousands of domains or specific URLs are on a static
blacklist, and
2) there is a small list of words which, if present in a URL, will
dynamically result in blocking.
The blocking is generally manifested as a "connection reset" page which
looks to most users like "page not found." China also poisons the DNS for
some of the domains it blocks, but this is (as far as I can tell) redundant
because of "1" above. (I guess it trips up some users whose VPN fails to
tunnel DNS requests.)
Sometimes (inconsistently), an attempt to see blocked content
results not only in the content not being delivered, but also a "punishment"
meted out to the offending user: all attempts to access servers outside
China fail for a period of between 5 and 10 minutes.
It's "2" above which can be used to censor searches, since
unencrypted access to Google from inside China (or to Baidu from outside
China) puts the search terms into the URL. This censorship can easily be
neutralised by accessing Google via HTTPS.
There are persistent reports that China's cybercensorship can
sometimes vary (a little) by ISP, but I've never seen this (I've only been
to ~13 of the 34 PRC-defined provinces), and Alkasir hasn't ever detected
any such variations. (The internet in 3 of those provinces isn't filtered:
Hong Kong, Macao, and Taiwan. Of course, even if the PRC thinks Taiwan's a
province, Taiwan doesn't think that.)
Best,
Eric
> -----Original Message-----
> From: liberationtech-boun...@lists.stanford.edu [mailto:liberationtech-
> boun...@lists.stanford.edu] On Behalf Of Philipp Winter
> Sent: Monday, 13 August 2012 16:15
> To: Stanford tech list
> Subject: Re: [liberationtech] Images of Blocking in Different Countries?
>
> On Sun, Aug 12, 2012 at 09:14:48PM -0700, Adam Fisk wrote:
> > My understanding is that China just shows a blank page. Is that correct?
>
> That depends on the type of filtering. The keyword filtering
infrastructure
> forcefully terminates connections and depending on the browser you will
get an
> error message saying something like "The connection was reset".
>
> You can actually test it yourself by going to baidu.com and searching for
> "falun".
>
> Philipp
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