SlotSwapper: A schedule randomization protocol for real-time wirelessHART networks

Industrial process control systems are time-critical systems where reliable communications between sensors and actua- tors need to be guaranteed within strict deadlines to main- tain safe operation of all the components of the system. WirelessHART is the most widely adopted standard which serves as the medium of communication in industrial se- tups due to its support for Time Division Multiple Access (TDMA) based communication, multiple channels, chan- nel hopping, centralized architecture, redundant routes and avoidance of spatial re-use of channels. However, the com- munication schedule in WirelessHART network is decided by a centralized network manager at the time of network initialization and the same communication schedule repeats every hyper-period. Due to predictability in the time slots of the communication schedule, these systems are vulnera- ble to timing attacks which eventually can disrupt the safety of the system. In this work, we present a moving target defense mechanism, the SlotSwapper, which uses schedule randomization techniques to randomize the time slots over a hyper-period schedule, while still preserving all the feasi- bility constraints of a real-time WirelessHART network and makes the schedule uncertain every hyper-period. We tested the feasibility of the generated schedules on random topolo- gies with 100 simulated motes in Cooja simulator. We use schedule entropy to measure the confidentiality of our al- gorithm in terms of randomness in the time slots of the generated schedules.