Games without Frontiers: Investigating Video Games as a Covert Channel

The Internet has become a critical communication infrastructure for citizens to organize protests and express dissatisfaction with their governments. This fact has not gone unnoticed, with governments clamping down on this medium via censorship, and circumvention researchers working to stay one step ahead. In this paper, we explore video games as a new avenue for covert channels. Two features make video games attractive for use as a cover protocol in censorship circumvention tools: First, games within a genre share many common features. Second, there are many different games, each with their own protocols and server infrastructures. These features allow circumvention tool developers to build a single framework that can be adapted to work with many different games within a genre; therefore allowing quick response to censor created blockades. In addition, censored users can diversify their covert communications across many different games, making it difficult for a censor to respond by simply blocking a single covert channel. We demonstrate the feasibility of this approach by implementing our circumvention scheme over three real-time strategy games (including two best-selling closed-source games). We evaluate the security of our system prototype, Castle, by quantifying its resilience to a censor-adversary, similarity to real game traffic, and ability to avoid common pitfalls in covert channel design. We use our prototype to demonstrate that our approach can provide the throughput necessary for bootstrapping higher bandwidth channels and also the transfer of textual data, such as web articles, e-mail, SMS messages, and tweets, which are commonly used to organize political actions.