# Special Issue on Security and Privacy in Blockchains and the IoT Volume II
###### Abstract
(2016) specifically consider wireless sensor networks (WSNs), which are the enabler technology for the IoT. Since the devices deployed in these networks are usually rather rudimentary, they often lack sufficient security measures, which is why they are prone to cyberattacks. In their work, the authors therefore address the question of which protection goals are particularly relevant in WSNs and which unique characteristics of WSNs impede security measures. Furthermore, they investigate which cyberattacks are particularly prevalent and effective in the WSN context and how they affect the WSN. As existing security measures are insufficient against these attacks, the paper proposes the inclusion of blockchain technologies and machine learning techniques in WSNs. It also identifies challenges in this regard and discusses different implementation strategies to ensure reliable cyberattack detection and cyberattack prevention. The second review covers a specialized application domain involving WSN technologies. [PERSON] et al. [PERSON] et al. (2017) examine the Internet of Robotic Things (IoRT), which supplements the IoT with concepts of cloud computing and artificial intelligence to enable cyber-physical systems to make autonomous decisions and carry out appropriate actions. The IoRT can be leveraged in various fields, including manufacturing, healthcare, security, and transportation. In their review, the authors outline the techniques used in IoRT, the relevant architectures in the IoRT landscape, and the capabilities of cyber-physical systems in this context. The gained insights provide the foundation for taxonomies that reflect the different classes into which IoRT environments can be categorized. The review also addresses security aspects that are characteristic for the IoRT. It is noticeable that there are still major limitations related to data security, for which the authors also suggest the use of blockchaintechnologies. The paper concludes with open research questions, including ethical issues, trust issues, and data quality issues. The final review brings the blockchain topic to the forefront. Blockchain technology offers a high level of data protection, as all data are stored in an immutable manner, and tampering with the data is impossible. However, this very characteristic is also an inherent problem of this technology when it comes to data privacy. Data protection laws such as the GDPR grant data subjects a right to rectification (Art. 16 GDPR) as well as a right to erasure (Art. 17 GDPR). That is, whenever personal data are stored in a blockchain-based data repository, there have to be redacting capabilities. [PERSON] et al. [18] therefore investigate which concepts towards a mutable blockchain, which allows controlled and supervised amendments to specific content, are discussed in research. In this respect, they also identify the particular implementation challenges that a redactable blockchain has to overcome and address security criteria that must still apply despite the redacting capabilities. Based on their findings, the authors outline future research directions and open issues in the field of effective redaction mechanisms for blockchain technologies. The seventeen excellent papers included in this Special Issue provide a well-rounded overview of the current state of the art and current state of research in the field of security and privacy issues in blockchain technologies and the IoT. In this respect, it illustrates how versatile and complex this topic area is. On the one hand, the literature reviews highlight the potential of these technologies and how they can significantly facilitate our everyday lives in all kinds of domains, but also which open research questions still need to be solved in the future when it comes to security and privacy. On the other hand, the research articles present highly innovative approaches to overcome such problems without having to sacrifice the conveniences that blockchain technologies and the IoT have to offer.