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With the advent of Industry 4.0, industrial facilities and critical infrastructures are transforming into an ecosystem of heterogeneous physical and cyber components, such as programmable logic controllers, increasingly interconnected and therefore exposed to cyber-physical attacks, i.e., security breaches in cyberspace that may adversely affect the physical processes underlying industrial control systems. In this paper, we propose a formal approach based on runtime enforcement to ensure specification compliance in networks of controllers, possibly compromised by colluding malware that may tamper with actuator commands, sensor readings, and inter-controller communications. Our approach relies on an ad-hoc sub-class of Ligatti et al.'s edit automata to enforce controllers represented in Hennessy and Regan's Timed Process Language. We define a synthesis algorithm that, given an alphabet $P$ of observable actions and a timed correctness property $e$, returns a monitor that enforces the property $e$ during the execution of any (potentially corrupted) controller with alphabet $P$, and complying with the property $e$. Our monitors correct and suppress incorrect actions coming from corrupted controllers and emit actions in full autonomy when the controller under scrutiny is not able to do so in a correct manner. Besides classical requirements, such as transparency and soundness, the proposed enforcement enjoys deadlock- and diverge-freedom of monitored controllers, together with scalability when dealing with networks of controllers. Finally, we test the proposed enforcement mechanism on a non-trivial case study, taken from the context of industrial water treatment systems, in which the controllers are injected with different malware with different malicious goals.

We define a simple process calculus, based on Hennessy and Regan's Timed Process Language, for specifying networks of communicating programmable logic controllers (PLCs) enriched with monitors enforcing specifications compliance. We define a synthesis algorithm that given an uncorrupted PLC returns a monitor that enforces the correctness of the PLC, even when injected with malware that may forge/drop actuator commands and inter-controller communications. Then, we strengthen the capabilities of our monitors by allowing the insertion of actions to mitigate malware activities. This gives us deadlock-freedom monitoring: malware may not drag monitored controllers into deadlock states., 21-st Italian Conference on Theoretical Computer Science (ICTCS 2020). CEUR Workshop Proceedings

We apply formal methods to lay and streamline theoretical foundations to reason about Cyber-Physical Systems (CPSs) and physics-based attacks, i.e., attacks targeting physical devices. We focus on a formal treatment of both integrity and denial of service attacks to sensors and actuators of CPSs, and on the timing aspects of these attacks. Our contributions are fourfold. (1)~We define a hybrid process calculus to model both CPSs and physics-based attacks. (2)~We formalise a threat model that specifies MITM attacks that can manipulate sensor readings or control commands in order to drive a CPS into an undesired state, and we provide the means to assess attack tolerance/vulnerability with respect to a given attack. (3)~We formalise how to estimate the impact of a successful attack on a CPS and investigate possible quantifications of the success chances of an attack. (4)~We illustrate our definitions and results by formalising a non-trivial running example in Uppaal SMC, the statistical extension of the Uppaal model checker; we use Uppaal SMC as an automatic tool for carrying out a static security analysis of our running example in isolation and when exposed to three different physics-based attacks with different impacts., Comment: This document extends the paper "A Formal Approach to Physics-Based Attacks in Cyber-Physical Systems" that will appear in ACM Transactions on Privacy and Security by providing proofs that are worked out in full details. arXiv admin note: text overlap with arXiv:1611.01377

Industrial facilities and critical infrastructures are transforming into "smart" environments that dynamically adapt to external events. The result is an ecosystem of heterogeneous physical and cyber components integrated in cyber-physical systems which are more and more exposed to cyber-physical attacks, i.e., security breaches in cyberspace that adversely affect the physical processes at the core of the systems. We provide a formal compositional metric to estimate the impact of cyber-physical attacks targeting sensor devices of IoT systems formalised in a simple extension of Hennessy and Regan's Timed Process Language. Our impact metric relies on a discrete-time generalisation of Desharnais et al.'s weak bisimulation metric for concurrent systems. We show the adequacy of our definition on two different attacks on a simple surveillance system.

Gossip protocols have been proposed as a robust and efficient method for disseminating information throughout large-scale networks. In this paper, we propose a compositional analysis technique to study formal probabilistic models of gossip protocols expressed in a simple probabilistic timed process calculus for wireless sensor networks. We equip the calculus with a simulation theory to compare probabilistic protocols that have similar behaviour up to a certain tolerance. The theory is used to prove a number of algebraic laws which revealed to be very effective to estimate the performances of gossip networks, with and without communication collisions, and randomised gossip networks. Our simulation theory is an asymmetric variant of the weak bisimulation metric that maintains most of the properties of the original definition. However, our asymmetric version is particularly suitable to reason on protocols in which the systems under consideration are not approximately equivalent, as in the case of gossip protocols.

We propose a process calculus for modelling systems in the Internet of Things paradigm. Our systems interact both with the physical environment, via sensors and actuators, and with smart devices, via short-range and Internet channels. The calculus is equipped with a standard notion of bisimilarity which is a fully abstract characterisation of a well-known contextual equivalence. We use our semantic proof-methods to prove run-time properties as well as system equalities of non-trivial IoT systems., The contribution of Valentina Castiglioni is limited to an early writing of some of the proofs in the Appendix

We model a timing attack on web privacy proposed by Felten and Schneider by using three different approaches: HL-Timed Automata, SMV model checker, and tSPA Process Algebra. Some comparative analysis on the three approaches is derived.

Hybrid systems is a suitable model to describe systems composed of both continuous and discrete components. The continuous components typically represent physic events. The discrete components are logic devices, such as switches and digital circuitry. A typical example is a system where physical processes are controlled by embedded controllers. Different classes of hybrid systems have been proposed. In this paper we consider hybrid systems equipped with real variable (as usual), integer variables and unbounded arrays. We study the expressive power of five classes: Linear real hybrid systems, Polynomial real hybrid systems, Mixed hybrid systems, D-hybrid systems and S-hybrid systems. For these classes there exists a quantifier elimination technique for computing the successor operator, hence the reachability problem is semidecidable., Journal of Automata, Languages and Combinatorics, Volume 12, Number 3, 2007, 373-405

Gossip protocols have been proposed as a robust and efficient method for disseminating information throughout large-scale networks. In this paper, we propose a compositional analysis technique to study formal probabilistic models of gossip protocols expressed in a simple probabilistic timed process calculus for wireless sensor networks. We equip the calculus with a simulation theory to compare probabilistic protocols that have similar behaviour up to a certain tolerance. The theory is used to prove a number of algebraic laws which revealed to be very effective to estimate the performances of gossip networks, with and without communication collisions, and randomised gossip networks. Our simulation theory is an asymmetric variant of the weak bisimulation metric that maintains most of the properties of the original definition. However, our asymmetric version is particularly suitable to reason on protocols in which the systems under consideration are not approximately equivalent, as in the case of gossip protocols., Logical Methods in Computer Science ; Volume 14, Issue 3 ; 186-05974

Cyber-Physical Systems (CPSs) are integrations of distributed computing systems with physical processes via a networking with actuators and sensors, where feedback loops among the components allow the physical processes to affect the computations and vice versa. Although CPSs can be found in several complex and sometimes critical real-world domains, their verification and validation often relies on simulation-test systems rather then automatic methodologies to formally verify safety requirements. In this work, we prove the decidability of the reachability problem for discrete-time linear CPSs whose physical process in isolation has a periodic behavior, up to an initial transitory phase.