# Special Issue on Security and Privacy in Blockchains and the IoT Volume II
###### Abstract  
In this day and age, data are indispensable commodities and have become an integral part of our daily lives. In fact, it is no coincidence that data are referred to as the oil of the 21 st century, as they are the key drivers for all kinds of smart services: In the private sector, we rely on streaming providers to recommend songs or videos tailored to our preferences. In the healthcare sector, we benefit from the fact that important information, such as emergency data or a medication plan, is automatically registered and merged in an electronic patient file and thereby made immediately available to treating physicians. In manufacturing, predictive maintenance, i.e., the proactive maintenance of machines at an early stage, can minimize downtimes and, thus, delays in the production process. Besides these three examples from the domains of smart homes, smart healthcare, and smart manufacturing, there are countless other smart services in these and virtually any other conceivable domain. Such smart services are enabled primarily by the continuous collection and comprehensive analysis of data. From a technical point of view, two key requirements have to be addressed: On the one hand, there is a need to capture, quantify, and interconnect a wide range of aspects. This can be achieved by means of the Internet of Things (IoT). Here, physical everyday objects are equipped with sensors and connectivity capabilities. Such objects are usually referred to as smart things. The sensors are able to record data about their environment and map them to a digital twin--a virtual representation of the everyday object they are connected to. For their part, these digital twins can create networks to communicate captured information with their surroundings. On the other hand, it is necessary to make the collected data reliably available to all authorized stakeholders. Distributed ledger technologies (DLTs) enable the management and provisioning of shared data collections in a trusted manner. To this end, there is not a central instance that maintains (and thus controls) the data, but the data are managed in multiple replicas across a distributed network. Here, it is ensured that any changes are always reflected in all copies of the ledger and that all parties involved agree on the currently valid state of the ledger using a consensus mechanism. Blockchain is the most prevalent example of distributed ledger technology, which is why these two terms are often used synonymously. However, since data are not simply commodities that facilitate and enrich our everyday lives thanks to smart services but also have a high economic value, security aspects must be given special consideration in any activities involving data processing. For instance, it is essential to ensure that access to the collected data can be restricted, that data tampering can be prevented, and that the availability of the data cannot be impaired, e.g., by illegitimate deletion or denial-of-service attacks. These aspects are addressed by the three IT protection goals of 'confidentiality', 'integrity', and 'availability'. In addition to the established CIA triad, consisting of the aforementioned three IT protection goals, the protection goal 'privacy' is assuming an increasingly decisive role nowadays. This special status is due tothe fact that smart things are ubiquitous in our everyday lives. As a result, more and more sensitive data are being collected and processed, providing comprehensive insights into the personal lives of the data subjects. In this Special Issue, fourteen research articles and three literature reviews therefore address research questions in the thematic area of security and privacy in blockchains and the IoT, while Volume I [1] addresses general security and privacy aspects in the context of blockchain technologies and the IoT, the focus of Volume II is rather on a holistic understanding that, for instance, takes into account mutual effects between individual protection goals and end-to-end security measures from acquisition to provisioning.