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 <cra...@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-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**** > > > _______________________________________________**** > > > liberationtech mailing list**** > > > liberationtech@lists.stanford.edu**** > > > **** > > > Should you need to change your subscription options, please go to:**** > > > **** > > > https://mailman.stanford.edu/mailman/listinfo/liberationtech**** > > > **** > > > If you would like to receive a daily digest, click "yes" (once you click > above) next**** > > > to "would you like to receive list mail batched in a daily digest?"**** > > > **** > > > You will need the user name and password you receive from the list > moderator**** > > > in monthly reminders. You may ask for a reminder here:**** > > > https://mailman.stanford.edu/mailman/listinfo/liberationtech**** > > > **** > > > Should you need immediate assistance, please contact the list moderator. > **** > > > **** > > > Please don't forget to follow us on http://twitter.com/#!/Liberationtech > **** > > _______________________________________________ > liberationtech mailing list > liberationtech@lists.stanford.edu > > Should you need to change your subscription options, please go to: > > https://mailman.stanford.edu/mailman/listinfo/liberationtech > > If you would like to receive a daily digest, click "yes" (once you click > above) next to "would you like to receive list mail batched in a daily > digest?" > > You will need the user name and password you receive from the list > moderator in monthly reminders. You may ask for a reminder here: > https://mailman.stanford.edu/mailman/listinfo/liberationtech > > Should you need immediate assistance, please contact the list moderator. > > Please don't forget to follow us on http://twitter.com/#!/Liberationtech >
_______________________________________________ liberationtech mailing list liberationtech@lists.stanford.edu Should you need to change your subscription options, please go to: https://mailman.stanford.edu/mailman/listinfo/liberationtech If you would like to receive a daily digest, click "yes" (once you click above) next to "would you like to receive list mail batched in a daily digest?" You will need the user name and password you receive from the list moderator in monthly reminders. You may ask for a reminder here: https://mailman.stanford.edu/mailman/listinfo/liberationtech Should you need immediate assistance, please contact the list moderator. Please don't forget to follow us on http://twitter.com/#!/Liberationtech
