A Malware-Tolerant, Self-Healing Industrial Control System Framework

Industrial Control Systems (ICSs) are computers managing many critical infrastructures like power plants, aeroplanes, production lines, etc. While ICS were specialised hardware circuits without internet connection in former times, they are nowadays commodity computers with network connection, TCP/IP stack, and a full operating system, making them vulnerable to common attacks. The defensive mechanisms, however, are still lacking behind due to the strong requirement for availability of ICSs which prohibits to deploy typical countermeasures like e.g. an anti-virus. New techniques are needed to defend these systems under their distinct prerequisites. We introduce the concept of a malware-tolerant ICS network architecture which can still operate securely even when some components are entirely compromised by an attacker. This was done by replacing all single pointof-failures with multiple components verifying each other. We provide ProVerif proofs to show the correctness of the network protocol one-byone assuming each device compromised. Furthermore, we added a self-healing mechanism based on invariants to the architecture on network as well as system level which will reset failed or compromised systems. To demonstrate system level self-healing, we implemented it on top of FreeRTOS and ARM TrustZone. The network level self-healing was incorporated into the ProVerif proofs by formally verifying the absence of type 1 (falsely identified attacks) and type 2 errors (missed attacks).