Network-Based Secret Communication in Clouds: A Survey

The cloud concept promises computing as a utility. More and more functions are moved to cloud environments. But this transition comes at a cost: security and privacy solutions have to be adapted to new challenges in cloud environments. We investigate secret communication possibilities-data transmission concealing its mere existence or some of its characteristics-in clouds. The ability to establish such secret communication provides a powerful instrument to adversaries and can be used to gather information for attack preparation, to conceal the coordination of malicious instances or to leak sensitive data. In this paper, we investigate potentials for secret communication in cloud environments and show possible application scenarios. We survey current approaches of different kinds of secret communication including covert channels, side channels, and obfuscation techniques. While most existing work focuses on covert and side channels within a physical server (cross-VM channels), we place emphasis on network-based covert and side channels, which are rarely addressed in current literature about cloud security. We then discuss secret communication techniques with respect to the application scenarios and show their advantages and limitations.