Biblio

A hardware Trojan is a malicious circuit inserted into a device by a malicious designer or manufacturer in the circuit design or fabrication phase. With the globalization of semiconductor industry, more and more chips and devices are designed, integrated and fabricated by untrusted manufacturers, who can potentially insert hardware Trojans for launching attacks after the devices are deployed. Moreover, the most damaging attack in a smart grid is a large scale electricity failure, which can cause very serious consequences that are worse than any disaster. Unfortunately, this attack can be implemented very easily by synchronized hardware Trojans acting as a collective offline time bomb; the Trojans do not need to interact with one another and can affect a large fraction of nodes in a power grid. More sophisticatedly, this attack can also be realized by online hardware Trojans which keep listening to the communication channel and wait for a trigger event to trigger their malicious payloads; here, a broadcast message triggers all the Trojans at the same time. In this paper, we address the offline synchronized hardware Trojan attack, as it does not require the adversary to penetrate the power grid network for sending triggers. We classify two types of offline synchronized hardware Trojan attacks as type A and B: type B requires communication between different nodes, and type A does not. The hardware Trojans needed for type B turn out to be much more complex (and therefore larger in area size) than those for type A. In order to prevent type A attacks we suggest to enforce each power grid node to work in an unique time domain which has a random time offset to Universal Coordinated Time (UTC). This isolation principle can mitigate type A offline synchronized hardware Trojan attacks in a smart grid, such that even if hardware Trojans are implanted in functional units, e.g. Phasor Measurement Units (PMUs) and Remote Terminal Units (RTUs), they can only cause a minimal damage, i.e. sporadic single node failures. The proposed solution only needs a trusted Global Positioning System (GPS) module which provides the correct UTC together with small additional interface circuitry. This means that our solution can be used to protect the current power grid infrastructure against type A offline attacks without replacing any untrusted functional unit, which may already have embedded hardware Trojans.