The fifth-generation (5G) technology standard in telecommunications is expected to support ultra-reliable low latency communication to enable real-time applications such as industrial automation and control. 5G configured grant (CG) scheduling features a pre-allocated periodicity-based scheduling approach, which reduces control signaling time and guarantees service quality. Although this enables 5G to support hard real-time periodic traffics, synthesizing the schedule efficiently and achieving high resource efficiency, while serving multiple communications, are still an open problem. In this work, we study the trade-off between scheduling flexibility and control overhead when performing CG scheduling. To address the CG scheduling problem, we first formulate it using satisfiability modulo theories (SMT) so that an SMT solver can be used to generate optimal solutions. To enhance scalability, we propose two heuristic approaches. The first one as the baseline, Co1, follows the basic idea of the 5G CG scheduling scheme that minimizes the control overhead. The second one, CoU, enables increased scheduling flexibility while considering the involved control overhead. The effectiveness and scalability of the proposed techniques and the superiority of CoU compared to Co1 have been evaluated using a large number of generated benchmarks as well as a realistic case study for industrial automation.

This article presents a methodology for cross-layer control–communication co-synthesis of cyber-physical systems (CPSs), communicating over Ethernet networks, with stability guarantees. We consider the recently developed IEEE 802.1 Time-Sensitive Networking standards for real-time Ethernet communication, in particular 802.1Qbv-2015, which is gaining traction in automotive and industrial automation applications. Specifically, we address routing and static scheduling of Ethernet control packets in a CPS with a switched Ethernet communication network connecting sensors, computers, and actuators. The design problem spans the network and control application layers. Our proposed SMT-based solution integrates many decision variables and objectives related to message routing, scheduling, and control application stability.

Security for outsourced control applications can be provided if the physical plant is enabled with a mechanism to verify the control signal received from the cloud. Recent developments in modern cryptography claim the applicability of verifiable computation techniques. Such techniques allow a client to check the correctness of a remote execution. This article delivers a proof of concept for applicability of the verifiable computation scheme to control applications over the cloud. We showcase the practicality of verifiable computation on physical plants with different timing demands and deliver a real-life example using a watertank system as the client and Microsoft Azure as the cloud. We show the effectiveness of the verifiable computation scheme on cloud-based implementation of advanced control methods, such as Model Predictive Control.

With cyber-physical systems opening to the outside world, security can no longer be considered a secondary issue. In this work, we focus on security threats to control applications in cyber-physical systems. We provide detection, prevention, and mitigation solutions to attacks considering the stringent resource constraints and important properties of such systems. 

First, we highlight some important properties of control applications that are used to design an intrusion detection and mitigation mechanism. We show how the control laws, derived from the physical properties of control applications, can facilitate the intrusion detection mechanism. We also use a resource management approach to maintain the performance of the control application under attack. 

Second, we elaborate on the challenges derived from sharing a processor among several controller tasks. We investigate the counter-intuitive timing anomalies that result from such resource sharing and introduce the Butterfly attack which exploits these anomalies. With the Butterfly attack, the adversary interferes with a low criticality and less protected task to change the timing behavior of the other tasks sharing the same platform. We experimentally show how this attack can indirectly destabilize a high criticality and, potentially, more protected task. 

Then, we consider real-time communication of control applications over a Time-Triggered Ethernet network. We demonstrate the impact of varying delays on control stability and identify the route and schedule constraints that are necessary to guarantee stability. On top of that, we study the impact of encryption and decryption delays on stability and employ a design space exploration approach to maximize security while continuing to satisfy stability guarantees. 

Today, it is common knowledge in the cyber-physical systems domain that the tight interaction between the cyber and physical elements provides the possibility of substantially improving the performance of these systems that is otherwise impossible. On the downside, however, this tight interaction with cyber elements makes it easier for an adversary to compromise the safety of the system. This becomes particularly important, since such systems typically are composed of several critical physical components, e.g., adaptive cruise control or engine control that allow deep intervention in the driving of a vehicle. As a result, it is important to ensure not only the reliability of such systems, e.g., in terms of schedulability and stability of control plants, but also resilience to adversarial attacks.

In this article, we propose a security-aware methodology for routing and scheduling for control applications in Ethernet networks. The goal is to maximize the resilience of control applications within these networked control systems to malicious interference while guaranteeing the stability of all control plants, despite the stringent resource constraints in such cyber-physical systems. Our experimental evaluations demonstrate that careful optimization of available resources can significantly improve the resilience of these networked control systems to attacks.

Increasing internet connectivity poses an existential threat for cyber-physical systems. Securing these safety-critical systems becomes an important challenge. Cyber-physical systems often comprise several control applications that are implemented on shared platforms where both high and low criticality tasks execute together (to reduce cost). Such resource sharing may lead to complex timing behaviors and, in turn, counter-intuitive timing anomalies that can be exploited by adversaries to destabilize a critical control system, resulting in irreversible consequences. We introduce the butterfly attack, a new attack scenario against cyber-physical systems that carefully exploits the sensitivity of control applications with respect to the implementation on the underlying execution platforms. We illustrate the possibility of such attacks using two case-studies from the automotive and avionic domains.