1. Introduction

Security of a computer system has been traditionally related to the security of the software or the information being processed. The underlying hardware used for information processing has been considered as the proverbial “root of trust” or trust anchors. Malicious hardware modifications – e.g., hardware Trojan attacks, which brought to light just a decade ago – are potent attacks on electronic hardware that violates the fundamental assumption of the hardware root of trust. These attacks, in the form of malicious modifications of electronic hardware at different stages of its life cycle, pose major security concerns in the electronics industry. An adversary can mount such an attack with an objective to cause in-field operational failure potentially leading to catastrophic consequences or to leak secret information from a chip – e.g., the key in a cryptographic chip, to an unauthorized party. The global economic trend that encourages increased reliance on untrusted entities in the hardware design and fabrication process is rapidly enhancing the vulnerability to such attacks. This book ventures an all-inclusive approach to illustrate the threats originating from hardware Trojan attacks, present different Trojan attack models with elaborate description on the types and scenarios, and describe existing trust metrics and various forms of protection approaches, defenses, and future research directions. The research progress on hardware Trojan is remarkable in academia and industrial arena. The research activities in this area have grown significantly over the decade with new vulnerabilities and solutions frequently reported by researchers across the globe.