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Trojans and Trojan Detection Techniques

In this section, we describe the characteristics of hardware Trojan horses, taxonomies that have been proposed to classify them and design defenses. We also review selected defense methodologies that are proposed in the literature.

Trojan Characteristics

A first step toward estimating the risk of a hardware Trojan horse insertion and designing efficient and appropriate defenses is to consult a classification of Trojans. The engineering challenge is rather big, as malevolent actors can use a multitude of methods to modify the functionality of their target for their own benefit.

One classification is based on the characteristics of the Trojans [21]. As depicted in Fig. 9.1, the characteristics of Trojans are the type, the payload, the trigger, the size, and its communication protocol.

  • • The type of the Trojan is the kind of the attack to the pointed circuit. Based on that, the Trojan can be functional or parametric.
  • • The payload is the effect that the Trojan will have to the system, the gain that the attacker with have from that attack. For most of the Trojans, the primary point is to steal the secret information that the system is designed to securely send to the outside world.
  • • The size of the Trojan is another important factor. The area that can cover could be from a small wire to a large gate. Of course, it is more usual and efficient to the attackers to use small sized Trojans, while it will benefit them to make the exposure of the Trojan more difficult.
  • • The communication protocol is the way the Trojan will communicate and affect the circuit. It could be stored to a peripheral device or directly inside the chip.
  • • Last but not least is the trigger point of the Trojan. Trigger refers to the way the Trojan will be activated. Some of the most common activation ways include changes to the temperature or the voltages of the system. Another way is related to changes on the logic of the circuit. For example the data on an input, an unexpected interrupt or changes at the clock of the system. Of course there are systems that they do not have a trigger point, which means that the Trojan can be triggered at any time.
Characteristics of hardware Trojans

Fig. 9.1 Characteristics of hardware Trojans

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