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[liberationtech] Images of Blocking in Different Countries?

Steve Weis steveweis at gmail.com
Wed Aug 15 09:55:56 PDT 2012


This paper "Ignoring the Great Firewall of China" is a few years old, but
at the time China was inspecting TCP packets for verboten keywords:
http://www.cl.cam.ac.uk/~rnc1/ignoring.pdf

The blocking was easy to circumvent. The researchers were able to just
ignore TCP reset packets and the connections proceeded unhindered. They
also were able to conduct a denial of service attack against IP addresses
in China by spoofing packets with forbidden content, which would trigger
spurious connection resets.

This was 6 years ago, so I'm sure the game has changed somewhat.

On Tue, Aug 14, 2012 at 11:46 PM, Eric S Johnson <crates at oneotaslopes.org>wrote:

> 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-bounces at lists.stanford.edu [mailto:liberationtech-*
> ***
>
> > bounces at 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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