China is known for its tight security when it comes to online services and content. Dubbed the "Great Firewall of China," the country's data filters prevent access to any domain or service deemed to potentially contain illegal or subversive content. Computer scientists have, however, found a way to get past China's data filters by embedding censored data within approved traffic.

"Telex," which will be formally launched at the Usenix security conference in San Francisco in August, basically smuggles banned content within allowed traffic. Public-key cryptography is used to hide banned data in encrypted form, which are smuggled within packets of legitimate traffic. Data is then reconstituted and decrypted at the destination, at which point the user has access to the website or information as if it weren't banned in the first place. 

Circumventing the Great Firewall

Current anti-censorship technologies rely on virtualization or firewalls to gain access to banned data and websites. For example, users can be connected to a server that is not within the coverage of the Great Firewall, either through proxy or through remote login. But these are easily banned once authorities discover the potential for getting past the censors.

With Telex, a user gains access to a banned website (let's call it site X), but a a client-based program instead requests for an allowed site (called site Y), and adds special markings to outbound request packets. Routers from around the world will then recognize these markings or signatures and instead retrieved site X. The content is then encrypted and the data broken down into pieces that come with the packets from site Y. Once the client receives the site Y data with encrypted site X packets, the original website is then decrypted and reconstituted. You now get to see site X.

But Will It Work?

Dr. Alex Halderman, one of the computer scientists working on Telex, says the team is already testing the system and has successfully viewed banned content from within China. However, the system still faces some challenges.

For one, ISPs and routers around the world would need a system that can spot the markers, and will also need the public encryption keys, so that these can route Telex traffic properly. Second, the team anticipates that censors might become more sophisticated in the future, which means even encrypted traffic could get banned.

The most difficult part is making sure the connections the user is making to an uncensored website that we use to disguise the censored content are convincing enough. That's the parameter we would adjust as the censor becomes more sophisticated."

Further, there is a need to deliver the Telex software to users in the first place, and the difficulty here is not being tagged as a piece of spyware or malware. Perhaps delivering the software on physical media can be a solution, and users can redistribute this from within the country.

Who Will Benefit?

China has some 470 million Internet users, most of whom get online through Chinese-language sites. However, some popular websites -- such as Twitter -- are banned because government fears these could be sources of discussion on dissent. Meanwhile, local companies such as Baidu and Weibo are planning their own international expansion, but with a tight firewall, the potential benefit seems to only go one way. A system like Telex can help level the playing field for online services, and will open better access opportunities to Chinese users.