How One Might Climb Over the Great Firewall

One minor irritation on my recent trip to China was discovering that Facebook and Google+, where I normally waste time arguing with people, were both blocked, as was blogspot and hence my own blog—the reason this post is only going up now, from Hong Kong. I gather that locals have ways of evading the restrictions but do not know the details. Which lets me try to figure out how I would do it.

The obvious solution is a proxy server. You connect to it from inside China, it connects you to any other site you like, blocked or not. The obvious problem is that whoever is doing the blocking notices and blocks the proxy server. To which one less obvious and so more interesting solution is …  .

Start with ten thousand proxy servers—or at least ten thousand URL’s, possibly all connected to the same hardware. You email each of your customers a URL to use. 

Unfortunately, some of your customers are spies, employees of whatever state organization does the blocking. They report the URL’s they get to their employer, who blocks them.

At which point you observe which URL's are blocked and note which of your customers got those URL's, hence which of your customers you suspect of being spies. Since customers who got the blocked URL’s now cannot access your server, you send them new URL’s—a different new URL for each of them. You observe which of those get blocked. You now have a pretty good guess which of your customers are spies.

So you have one set of URL’s for the spies, another for everyone else. Whenever a URL gets blocked, you send the customers who had that one a new URL—and add those customers to your list of possible spies. You continue with a policy of sending real customers URL’s that don’t go to confirmed spies and updating your list of confirmed spies on the basis of which URL’s get blocked.

So far as I can tell it should work. I have no idea whether or not I have just reinvented something close to what already exists.