Tag Archives: chinese

Web browsing behind the great firewall of China

I sometimes spend time in China, and while there, I work remotely to my office and to my home computer. I do somewhat technical work that sometimes requires online research, and it’s annoying that a significant fraction of non-Chinese sites are unreachable from China.

The thing to remember is that the firewall isn’t there to keep me from working. I’m a Canadian passport holder, and they really don’t care what I read while in China. That explains certain curious omissions, such as the fact that TCP port 22 (ssh) is not blocked.

So, here I am, in China, with a Linux laptop, and I’d like to browse the web. Rather than take my chances with the firewall, I proxy the connection through my home computer’s apache daemon.

So, first I set up the proxy service on my apache. Make sure you’ve built the httpd with these configuration options:

--enable-mods-shared="proxy proxy-http proxy-connect"

These settings turn on the proxy service and set it to proxy HTTP traffic. The “proxy-connect” flag allows the httpd to be used as a reflector for SSL connections. If you want to visit a banking website, the data still travels as SSL between your laptop and the home machine, but the home machine just reflects the traffic to the bank without knowing what’s in the data stream (the home machine cannot decode that data, if it could, it would count as a man-in-the-middle compromise of the SSL stream).

Next, add some lines to the httpd configuration file. Mine’s in /etc/apache/httpd.conf.

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule proxy_connect_module modules/mod_proxy_connect.so

ProxyRequests On

Order deny,allow
Deny from all
Allow from

What this does is to enable proxying, but only on connections from localhost. I don’t want my httpd to be a proxy for any random person in the outside world.

Next, I set up my ssh on connections to my home computer. You can either add a switch like this to the invocation:

-L 8080:

or you can add a line to your ~/.ssh/config entry for the connection to the home computer:

LocalForward 8080

Now, you ssh into your home computer.

Finally, you start up firefox, and select the menu item:
Select “Manual proxy configuration”, and point your HTTP and SSL proxies at “localhost” with the port number 8080.

That’s it, now when you browse websites, the HTTP-related data stream appears simply as a pile of encrypted bits over your ssh connection. The firewall cannot know what websites you’re visiting, it can’t even tell that you’re visiting a website at all.

Important note: this system proxies the HTTP data. That means web pages, frames, images in the page, RSS feeds, and so on. It does not proxy UDP or post-connection traffic, like youtube videos. If your web browser has a plugin that downloads data from an external site, that plugin may not be using your proxy.

If you want to know what data is not passing through your proxy, you can run tcpdump in another window. Something like this:

tcpdump 'host  and not port 22'

where is the IP number of your external interface (not You may have to add a “-i” switch if your laptop has more than one network interface. This command will show you all traffic that is not going over the ssh connection.

Experiences compiling X11R7

Compiling and installing X11R7, x.org 7.3, was a bit more rough than the X11 compiles I used to perform. I used the build script supplied with the source packages. When it finished, apparently successfully, there were two problems whose solutions were not obvious.

First of all, OpenGL worked on my NVidia box, but not my ATI laptop.

Second, my Chinese fonts for traditional characters in Emacs looked different, much worse. The simplified Chinese characters still looked fine.

OK, what were the problems, and how did I fix them. First of all, the OpenGL issue. I compiled X11 the same way on both computers, why did OpenGL not work on the ATI laptop? Well, both NVidia and ATI ship closed-source binary blobs with support libraries. The difference is that NVidia supplies its own libGL.so, while ATI uses the one from x.org. So, somehow I was failing to compile and install the OpenGL stuff. This didn’t matter for the NVidia case, because it supplied all of the libraries required, but ATI doesn’t do that. I had compiled and installed libMesa, so OpenGL should have worked. The OpenGL component is compiled as part of the xorg-server-1.4 package, and its configure script is executed by the build script that came with x.org. Aha, but in order to compile OpenGL, you have to provide the configure script with the path of the libMesa source tree. The x.org build script doesn’t do that, so OpenGL is not built. The solution is to interrupt the build at the point where the xorg-server-1.4 is about to be built (you can edit the script and put in an ‘exit 0’ there, for instance), then configure, build, and install the xorg-server-1.4 archive by hand, remembering to tell it where the mesa source tree is located. Once that completes, you can continue the build with the xorg script (I just commented out all entries above the server compile and resumed).

Now, the font problem. My TTF fonts are in /usr/share/fonts, and I verified that the files there were being read when I asked Emacs to display Chinese characters. So, it appeared as if the Chinese TTF fonts were the ones that were looking bad. A bit of research showed that Emacs does not, as of version 22.1.1, use scalable fonts. So I decided that it probably wasn’t supposed to be using those TTF fonts. Now, I had kept my old X11R6 tree around in case of issues like this, so a quick comparison of directories showed that there were some Chinese PCF fonts in the old install that I had forgotten to copy to the new location. So, I copied these files into their location in the X11R7 tree, and Emacs was restored to its former behaviour with respect to the displaying of Chinese fonts. The fonts, by the way, are taipei15.pcf, taipei16.pcf, taipei24.pcf, taipei24k.pcf, and taipeil24.pcf.