Covert Timing Channel Analysis of Rate Monotonic Real-Time Scheduling Algorithm in MLS Systems

The modern digital battlesphere requires the development and deployment of multi-level secure computing systems and networks. A portion of these systems are necessarily be operating under real-time processing constraints. High assurance systems processing national security information must be analyzed for possible information leakages, including covert channels. In this paper we provide a mathematical framework for examining the impact the rate-monotonic real-time scheduling algorithm has on covert timing channels. We prove that in some system configurations, it would not be possible to completely close the covert channel due to the rate-monotonic timing constraints. In addition, we propose a simple method to formulate a security metric to compare covert channels in terms of the relative amount of possible information leakage