In our digital world, integrated circuits are present in nearly every moment of our daily life. Even when using the coffee machine in the morning, or driving our car to work, we interact with integrated circuits. The increasing spread of information technology in virtually all areas of life in the industrialized world offers a broad range of attack vectors. So far, mainly software-based attacks have been considered and investigated, while hardware-based attacks have attracted comparatively little interest. The design and production process of integrated circuits is mostly decentralized due to financial and logistical reasons. Therefore, a high level of trust has to be established between the parties involved in the hardware development lifecycle. During the complex production chain, malicious attackers can insert non-specified functionality by exploiting untrusted processes and backdoors. This work deals with the ways in which such hidden, non-specified functionality can be introduced into hardware systems. After briefly outlining the development and production process of hardware systems, we systematically describe a new type of threat, the hardware Trojan. We provide a historical overview of the development of research activities in this field to show the growing interest of international research in this topic. Current work is considered in more detail. We discuss the components that make up a hardware Trojan as well as the parameters that are relevant for an attack. Furthermore, we describe current approaches for detecting, localizing, and avoiding hardware Trojans to combat them effectively. Moreover, this work develops a comprehensive taxonomy of countermeasures and explains in detail how specific problems are solved. In a final step, we provide an overview of related work and offer an outlook on further research in this field.

The new field of cryptographic currencies and consensus ledgers, commonly referred to as blockchains, is receiving increasing interest from various different communities. These communities are very diverse and amongst others include: technical enthusiasts, activist groups, researchers from various disciplines, start ups, large enterprises, public authorities, banks, financial regulators, business men, investors, and also criminals. The scientific community adapted relatively slowly to this emerging and fast-moving field of cryptographic currencies and consensus ledgers. This was one reason that, for quite a while, the only resources available have been the Bitcoin source code, blog and forum posts, mailing lists, and other online publications. Also the original Bitcoin paper which initiated the hype was published online without any prior peer review. Following the original publication spirit of the Bitcoin paper, a lot of innovation in this field has repeatedly come from the community itself in the form of online publications and online conversations instead of established peer-reviewed scientific publishing. On the one side, this spirit of fast free software development, combined with the business aspects of cryptographic currencies, as well as the interests of today's time-to-market focused industry, produced a flood of publications, whitepapers, and prototypes. On the other side, this has led to deficits in systematization and a gap between practice and the theoretical understanding of this new field. This book aims to further close this gap and presents a well-structured overview of this broad field from a technical viewpoint. The archetype for modern cryptographic currencies and consensus ledgers is Bitcoin and its underlying Nakamoto consensus. Therefore we describe the inner workings of this protocol in great detail and discuss its relations to other derived systems.