Two American professors say they have a new, virtually foolproof way to beat Internet censorship using a tool they call CacheBrowser, which they promise to be especially effective against censorship in China.
The professors, John Holowczak and Amir Houmansadr, describe the tool in a paper published earlier this year. As they explain, their technique for circumventing censorship centers on leveraging content delivery networks, or CDNs.
CDNs are servers that host cached versions of website data. When you visit a major website, chances are you that the data you download does not come directly from the site’s main server, but instead from CDN servers close to your location.
The main purpose of CDNs is to make data delivery more reliable and faster by providing redundancy (with CDN caches, websites remain available if the main server becomes inaccessible) and shortening the distance that data needs to travel to reach end users (CDNs are usually physically closer to end users than are primary Web servers).
But CDNs can also be used to access content that would otherwise be blocked by censorship. That’s because censorship infrastructure, like China’s Great Firewall, usually doesn’t block CDN servers. If it did, it would prevent local access to a lot of uncensored content, since a single CDN can host data for thousands of sites.
In other words, there is no way for censorship authorities to block particular websites on CDNs without also blocking a large portion of other Internet traffic.
By accessing CDNs to deliver content that would otherwise be censored, CacheBrowser has several advantages over traditional anti-censorship tools, like Tor:
- As noted above, it is virtually impossible for censorship authorities to block CDNs without blocking most Internet traffic in general.
- It is much faster than using a proxy, since it does not require traffic to be rerouted through multiple paths in the way Tor does.
- Because users access CDN content directly, they do not need to give third parties access to their browsing data in the way that they would when passing traffic through a proxy server, Tor or VPN.
- It is harder for censorship authorities to detect people who are using the method to circumvent censorship.
The main challenge to the CacheBrowser anti-censorship approach, according to the paper, is that not all websites make their content available via CDNs. Those that don’t can’t be accessed using this method. But the paper authors suggest that CDNs are becoming the norm, even for smaller websites. Going forward, CacheBrowser may become a vital new tool in the fight against censorship in China and elsewhere.