incorporating the basic concepts of reliability. Since errors and failures are factors that affect the correct operation of system, those can and should be part of the security analysis. The idea of security lies in the triptych analysis, prediction, and optimization. Concepts such as Mean Time to Attack (MTTA) and Mean Time to Recovery (MTTR) (which are based on the existing incident response and mitigation plans) could be used in order to represent the operation of the system being analyzed. Some first attempts towards this direction have already been made through the use of patterns that combine security and reliability [7] and attack prediction using Markov models [8]. What is missing and is expected to be introduced in the following years is new methodologies that could define the system requirements by incorporating security (and privacy) with reliability (and safety), introducing a new research area under the broad term of security. This editorial presents the manuscripts accepted, after a careful peer-review process, for publication in the topic \"Cyber Security and Critical Infrastructures\" of the MDPI journals _Applied Sciences, Electronics, Future Internet, Sensors_, and _Smart Cities_. The second volume includes sixteen articles: one editorial article and fifteen original research papers describing current challenges, innovative solutions, and real-world experiences involving cybersecurity issues in critical infrastructures. One major aspect of a smart city involves traffic management using ICT technologies. These technologies come with new vulnerabilities that could expose sensitive data of citizens to hackers. The authors in [9] propose a selective encryption scheme using singular-value decomposition and chaotic systems in order to overcome such issues. The proposed method ensures the confidentiality of video streams originating from devices that have minimal resources and that are mostly used in a smart-traffic management systems. The NIS directive (which is now substituted by the NIS2 Directive) has identified several critical sectors, including transport, and the proposed method could be used as an efficient tool to secure the information that is created and transmitted through a smart traffic system. When dealing with attacks in critical infrastructures that are usually large complex systems interconnected with several others, the correct prioritization of vulnerabilities is rather a difficult exercise to take. The lack of a proper vulnerability assessment leaves the infrastructure exposed to several attacks that could have devastating physical outcomes when it supports critical services to citizens. The authors in [10] present a vulnerability prioritization model that can reveal characteristics of information-security-related vulnerabilities. Coping with node-edge risk calculation, the authors in [11] propose a vulnerability Correlation and Attack Graph-based node-edge Scoring System. These works reveal the continuous and crucial need for novel vulnerability analysis methods that are based on prioritization and risk analysis. Dealing with the security and privacy of information during transmission into a digital environment, the authors in [12] propose a GCN algorithm for detecting malicious digital certificates. Malicious certificates can be used in order to hide malicious activities from threat actors. In order to achieve an efficient detection of malicious certificates, the authors design a rules-based method for extracting certificate attributes from documents that are used as features for the classification algorithm. The proposed method is very promising and can be applied in several aspects of electronic transactions where digital certificates are used to link ownership of public keys with the entities that own them. In order to secure transmission of information against tampering and cracking, authors in [13] propose a novel secure communication method based on the message hash chain.