A hardware Trojan (HT) is defined as a malicious, intentional modification of a circuit design that results in undesired behavior when the circuit is deployed. SoCs that are ‘infected’ by a hardware Trojan may experience changes in their functionality or specification, may leak sensitive information, or may experience degraded or unreliable performance. Hardware Trojan poses a serious threat to any hardware design being deployed in a critical operation.

As the hardware Trojans are inserted at the hardware level, software-level countermeasures may be inadequate to address the threat posed by HT. Also, detection of Trojans in a hardware design is challenging as there is no golden version against which to compare a given design during verification. In theory, an effective way to detect a Trojan is to activate the Trojan and observe its effects, but a Trojan’s type, size, and location are unknown, and its activation is, most likely, a rare event. A Trojan can be, therefore, well hidden during the normal functional operation of the chip and activated only when the triggering condition is applied.