Modern society relies heavily on systems that operate within strict timing requirements such as in engine control units in automobiles, aircraft avionics and navigation systems, programmable logic controllers in manufacturing plants, industrial control systems in the electricity sector, and many hundreds of others. The recent advent of autonomous cars, drones and internet-of-things (IoT) further expands the reach of these "real-time systems". The limitations of such devices viz., small computing power, less memory, limited battery power, has serious consequences for security, specifically, they become much harder to protect and defend. This research develops systematic security mechanisms for real-time embedded systems in critical applications to control what can be observed about them.