Date: Mon, 08 Jul 2002 05:01:44 +0900 From: "Kim Okasawa" <kimokasawa@hotmail.com> To: freebsd-net@FreeBSD.ORG, freebsd-security@FreeBSD.ORG Subject: Methods to detect Internet censorship. Message-ID: <F94LZQWTRxoPsIc839x00009bd9@hotmail.com>
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Dear all,
First, I need to apologize because this question is not FreeBSD-specific,
but I believe I may be able to find some good answers or insights from here.
Currently I'm working on a research project about Internet censorship in
certain Asia and middle east countries. I need to find out which US
websites has been blocked by those countries (e.g. CNN, NY Times, Wall
Street Journal, etc.)
The problem I encountered is that I haven't found a good way to detect the
blocking. Here are a brief description of what is going on.
In certain countries such as China, Singapore, and some middle east
countries, goverments do NOT want their people to have access to US websites
and obtain 'sensitive' information. The most common way to achieve this is
to build a national 'firewall' to drop all packets that come from certain
foreign IP addresses (addresses that belongs to websites such as CNN, etc.)
Here's the diagram:
Censored country
+--------------------------------------------+
| +--- ... |
| | |
| +----------+ +--- ... |
| | National | | |
Internet ----------+--+ +-----+--- ... hosts inside |
(world) | | Firewall | | the country |
| +----------+ +--- ... |
| | |
| +--- ... |
+--------------------------------------------+
To detect which websites has been blocked by those national firewalls, I
have two ways and each encounters a problem.
1. Buy shell or dial-up accounts from ISPs in such countries and remotely do
a HTTP GET to see if the requested webpages come back.
Problem: I cannot get shell or dial-up accounts from all regions in every
countries because some of them either don't accept credit card or don't deal
with foreigners.
2. Use loose source routing to fix a gateway inside such countries and send
HTTP GET requests to US sites from my home. So idealy, the packet will
travel from my home, pass a host inside the censored country, then come back
to the US site that I specified. When the US site responds to the request,
the packet will follow the same route to the censored country, then back to
me. If the US site is being blocked by the country, then I will never
receive the packet.
Problem: Loose source routing is denied by many routers and *nix machines
such as Linux so this method is quite unreliable and can generate a lot of
false results.
Are there other inexpensive ways to detect the censorships? I'm open to any
possible methods.
Thank you all for the helps.
Best Regards,
Kim Okasawa
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