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We propose CRYSTAL framework for automated cybersecurity assurance of cyber-physical systems (CPS) at design-time and runtime. We build attack models and apply formal verification to recognize potential attacks that may lead to security violations. We focus on both communication and computation in designing the attack models. We build a monitor to check and manage security at runtime and use a reference model, called Tiny Digital Twin, in detecting attacks. The Tiny Digital Twin is an abstract behavioral model that is automatically derived from the state space generated by model checking during design-time. Using CRYSTAL, we are able to systematically model and check complex coordinated attacks. In this paper we discuss the applicability of CRYSTAL in security analysis and attack detection for different case studies, Temperature Control System (TCS), Pneumatic Control System (PCS), and Secure Water Treatment System (SWaT). We provide a detailed description of the framework and explain how it works in different cases.

This paper presents a method for detecting cyber-attacks in cyber-physical systems using a monitor. The method employs an abstract model called Tiny Twin, which is built at design time and is used at runtime to detect inconsistencies. Tiny Twin is a state transition system that represents the observable behavior of the system from the monitor point of view. We model the behavior of the system in the Rebeca modeling language and use Afra model checker to generate the state space. The Tiny Twin is built automatically, by abstracting the state space while keeping the observable actions and preserving the trace equivalence. For doing that we had to solve the complexities in the state space introduced by time-shifts, nondeterministic assignments and abstraction of internal actions. We formally define the state space as Concise Rebeca Timed Transition System (CRTTS), and then map CRTTS to an LTS. The LTS is then fed to a tool to abstract away the non-observable actions.

Software-intensive systems in most domains, from autonomous vehicles to health, are becoming predominantly parallel to efficiently manage large amount of data in short (even real-) time. There is an incredibly rich literature on languages for parallel computing, thus it is difficult for researchers and practitioners, even experienced in this very field, to get a grasp on them. With this work we provide a comprehensive, structured, and detailed snapshot of documented research on those languages to identify trends, technical characteristics, open challenges, and research directions. In this article, we report on planning, execution, and results of our systematic peer-reviewed as well as grey literature review, which aimed at providing such a snapshot by analysing 225 studies.

Convolutional Neural Networks (CNNs) have received great attention in the computer vision domain. However, CNNs are vulnerable to adversarial attacks, which are manipulations of input data that are imperceptible to humans but can fool the network. Several studies tried to address this issue, which can be divided into two categories: (i) training the network with adversarial examples, and (ii) optimizing the network architecture and/or hyperparameters. Although adversarial training is a sufficient defense mechanism, they suffer from requiring a large volume of training samples to cover a wide perturbation bound. Tweaking network activation functions (AFs) has been shown to provide promising results where CNNs suffer from performance loss. However, optimizing network AFs for compensating the negative impacts of adversarial attacks has not been addressed in the literature. This paper proposes the idea of searching for AFs that are robust against adversarial attacks. To this aim, we leverage the Simulated Annealing (SA) algorithm with a fast convergence time. This proposed method is called SARAF. We demonstrate the consistent effectiveness of SARAF by achieving up to 16.92%, 18.3%, and 15.57% accuracy improvement against BIM, FGSM, and PGD adversarial attacks, respectively, over ResNet-18 with ReLU AFs (baseline) trained on CIFAR-10. Meanwhile, SARAF provides a significant search efficiency compared to random search as the optimization baseline.

Industrial cybersecurity has risen as an important topic of research nowadays. The heavy connectivity by the Internet of Things (IoT) and the growth of cyberattacks against industrial assets cause this risen and attract attention to the cybersecurity field. While fostering current software applications and use-cases, the ubiquitous access to the Internet has also exposed operational technologies to new and challenging security threats that need to be addressed. As the number of attacks increases, their visibility decreases. An attack can modify the Cyber-Physical Systems (CPSs) quality to avoid proper quality assessment. They can disrupt the system design process and adversely affect a product’s design purpose. This working progress paper presents our approach to modeling, analyzing, and mitigating cyberattacks in CPS. We model the normal behavior of the application as well as cyberattacks with the help of Microsoft Security Development Lifecycle (SDL) and threat modeling approach (STRIDE). Then verify the application and attacks model using a model checking tool and propose mitigation strategies to decrease the risk of vulnerabilities. The results can be used to improve the system design to overcome the vulnerabilities.

We propose a method to detect attacks on sensors and controllers in cyber-physical systems. We develop a monitor that uses an abstract digital twin, Tiny Twin, to detect false sensor data and faulty control commands. The Tiny Twin is a state transition system that represents the observable behavior of the system from the monitor point of view. At runtime, the monitor observes the sensor data and the control commands, and checks whether the observed data and commands are consistent with the state transitions in the Tiny Twin. The monitor produces an alarm when an inconsistency is detected. We model the components of the system and the physical processes in the Rebeca modeling language and use its model checker to generate the state space. The Tiny Twin is built automatically by reducing the state space, keeping the observable behavior of the system, and preserving the trace equivalence. We demonstrate the method and evaluate it in detecting attacks using a temperature control system. 

Software systems are complicated, and the scientific and engineering methodologies for software development are relatively young. We need robust methods for handling the ever-increasing complexity of software systems that are now in every corner of our lives. In this paper we focus on asynchronous event-based reactive systems and show how we start from the requirements, move to actor-based Rebeca models, and formally verify the models for correctness. The Rebeca models include the details of the signals and messages that are passed at the network level including the timing, and can be mapped to the executable code. We show how we can use the architecture design and structured requirements to build the behavioral models, including Rebeca models, and use the state diagrams to write the properties of interest, and then use model checking to check the properties. The formally verified models can then be used to develop the executable code. The natural mappings among the models for requirements, the formal models, and the executable code improve the effectiveness and efficiency of the approach. It also helps in runtime monitoring and adaptation.

Software systems are complicated, and the scientific and engineering methodologies for software development are relatively young. Cyber-physical systems are now in every corner of our lives, and we need robust methods for handling the ever-increasing complexity of their software systems. Model-Driven Development is a promising approach to tackle the complexity of systems through the concept of abstraction, enabling analysis at earlier phases of development. In this paper, we propose a model-driven approach with a focus on guaranteeing safety using formal verification. Cyber-physical systems are distributed, concurrent, asynchronous and event-based reactive systems with timing constraints. The actor-based textual modeling language, Rebeca, with model checking support is used for formal verification. Starting from structured requirements and system architecture design the behavioral models, including Rebeca models, are built. Properties of interest are also derived from the structured requirements, and then model checking is used to formally verify the properties. This process can be performed in iterations until satisfaction of desired properties are ensured, and possible ambiguities and inconsistencies in requirements are resolved. The formally verified models can then be used to develop the executable code. The Rebeca models include the details of the signals and messages that are passed at the network level including the timing, and this facilitates the generation of executable code. The natural mappings among the models for requirements, the formal models, and the executable code improve the effectiveness and efficiency of the approach. 

The cloud computing paradigm provides remote computing resources to the cloud service consumers and businesses. When combined with Internet of Things (IoT), both technologies open up a wide range of new possibilities for more agile and flexible applications. However, guaranteed quality of service is essential in provisioning of cloud services, which makes Service Level Agreements (SLAs) a focal point in the cloud computing and IoT ecosystem. The SLA definition and modeling phase is crucial in establishing SLAs between service providers and consumers. This paper identifies that the research on definition and modeling of SLAs for cloud services in IoT is widely dispersed and there is a lack of a systematic and comprehensive literature review. Thus, in this paper we build on top of a previously conducted systematic mapping study on management of SLAs for cloud computing and IoT to perform a comprehensive systematic review and discuss sub-categorization of the definition and modeling aspects of SLAs for cloud services in IoT. Furthermore we analyze the extracted relevant literature, present commonalities in the studies, identify gaps and discuss opportunities for further research in the area.