Bridger Hahn, Rishab Nithyanand, Phillipa Gill et al.
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 a promising new avenue for covert channels: real-time strategy-video games. Video games have two key features that make them attractive cover protocols for censorship circumvention. First, due to the popularity of gaming platforms such as Steam, there are a lot of different video games, each with their own protocols and server infrastructure. Users of video-game-based censorship-circumvention tools can therefore diversify across many games, making it difficult for the censor to respond by simply blocking a single cover protocol. Second, games in the same genre have many common features and concepts. As a result, the same covert channel framework can be easily adapted to work with many different games. This means that circumvention tool developers can stay ahead of the censor by creating a diverse set of tools and by quickly adapting to blockades created by the censor. We demonstrate the feasibility of this approach by implementing our coding scheme over two real-time strategy-games (including a very popular closed-source game). We evaluate the security of our system prototype -- Castle -- by quantifying its resilience to a censor-adversary, its similarity to real game traffic, and its ability to avoid common pitfalls in covert channel design. We use our prototype to demonstrate that our approach can provide throughput which is amenable to transfer of textual data, such at e-mail, SMS messages, and tweets, which are commonly used to organize political actions.