| 1. |
- Alanwar, Amr, et al.
(författare)
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Data-Driven Set-Based Estimation using Matrix Zonotopes with Set Containment Guarantees
- 2022
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Ingår i: 2022 EUROPEAN CONTROL CONFERENCE (ECC). - : IEEE. ; , s. 875-881
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Konferensbidrag (refereegranskat)abstract
- We propose a method to perform set-based state estimation of an unknown dynamical linear system using a data-driven set propagation function. Our method comes with set-containment guarantees, making it applicable to safety-critical systems. The method consists of two phases: (1) an offline learning phase where we collect noisy input-output data to determine a function to propagate the state-set ahead in time; and (2) an online estimation phase consisting of a time update and a measurement update. It is assumed that known finite sets bound measurement noise and disturbances, but we assume no knowledge of their statistical properties. These sets are described using zonotopes, allowing efficient propagation and intersection operations. We propose a new approach to compute a set of models consistent with the data and noise-bound, given input-output data in the offline phase. The set of models is utilized in replacing the unknown dynamics in the data-driven set propagation function in the online phase. Then, we propose two approaches to perform the measurement update. Simulations show that the proposed estimator yields state sets comparable in volume to the 3 sigma confidence bounds obtained by a Kalman filter approach, but with the addition of state set-containment guarantees. We observe that using constrained zonotopes yields smaller sets but with higher computational costs than unconstrained ones.
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| 2. |
- Bjork, J., et al.
(författare)
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Dynamic Virtual Power Plant Design for Fast Frequency Reserves : Coordinating Hydro and Wind
- 2022
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Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; , s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- To ensure frequency stability in future low-inertia power grids, fast ancillary services such as fast frequency reserves (FFR) have been proposed. In this work, the coordination of conventional (slow) frequency containment reserves (FCR) with FFR is treated as a decentralized model matching problem. The design results in a dynamic virtual power plant (DVPP) whose aggregated output fulfills the system operator’s (SO’s) requirements in all time scales, while accounting for the capacity and bandwidth limitation of participating devices. This is illustrated in a 5-machine representation of the Nordic synchronous grid. In the Nordic grid, stability issues and bandwidth limitations associated with non-minimum phase zeros of hydropower is a well-known problem. By simulating the disconnection of a 1400 MW importing dc link, it is shown that the proposed DVPP design allows for coordinating fast FFR from wind, with slow FCR from hydro, while respecting dynamic limitations of all participating devices. The SO’s requirements are fulfilled in a realistic low-inertia scenario without the need to install battery storage or to waste wind energy by curtailing the wind turbines.
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| 3. |
- Chen, Jianqi, et al.
(författare)
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Geometrical Characterization Of Sensor Placement For Cone-Invariant And Multi-Agent Systems Against Undetectable Zero-Dynamics Attacks\Ast
- 2022
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Ingår i: SIAM Journal of Control and Optimization. - : Society for Industrial & Applied Mathematics (SIAM). - 0363-0129 .- 1095-7138. ; 60:2, s. 890-916
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Tidskriftsartikel (refereegranskat)abstract
- Undetectable attacks are an important class of malicious attacks threatening the security of cyber-physical systems, which can modify a system's state but leave the system output measurements unaffected and hence cannot be detected from the output. This paper studies undetectable attacks on cone-invariant systems and multi-agent systems. We first provide a general characterization of zero-dynamics attacks, which characterizes fully undetectable attacks targeting the nonminimum phase zeros of a system. This geometrical characterization makes it possible to develop a defense strategy seeking to place a minimal number of sensors to detect and counter the zero-dynamics attacks on the system's actuators. The detect and defense scheme amounts to computing a set containing potentially vulnerable actuator locations and nodes and a defense union for feasible placement of sensors based on the geometrical properties of the cones under consideration.
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| 4. |
- Emad, Sawsan, et al.
(författare)
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Privacy Guarantees for Cloud-based State Estimation using Partially Homomorphic Encryption
- 2022
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Ingår i: 2022 European Control Conference (ECC). - : IEEE. - 9783907144077 - 9781665497336 ; , s. 98-105
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Konferensbidrag (refereegranskat)abstract
- The privacy aspect of state estimation algorithms has been drawing high research attention due to the necessity for a trustworthy private environment in cyber-physical systems. These systems usually engage cloud-computing platforms to aggregate essential information from spatially distributed nodes and produce desired estimates. The exchange of sensitive data among semi-honest parties raises privacy concerns, especially when there are coalitions between parties. We propose two privacy-preserving protocols using Kalman filter and partially homomorphic encryption of the measurements and estimates while exposing the covariances and other model parameters. We prove that the proposed protocols achieve satisfying computational privacy guarantees against various coalitions based on formal cryptographic definitions of indistinguishability. We evaluate the proposed protocols to demonstrate their efficiency using data from a real testbed.
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| 5. |
- He, Xingkang, et al.
(författare)
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Secured Filters Based on Saturated Innovations
- 2022
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Ingår i: Security and Resilience of Control Systems. - Cham : Springer Nature. ; , s. 3-29
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter, we study how to design secure centralized and distributed filters for linear time-invariant systems with bounded noise under false data injection attacks in sensor networks. An adversary is able to compromise a subset of sensors and manipulate the measurements arbitrarily. We provide two motivating examples for this problem setup from smart buildings and autonomous vehicles. Then we design a centralized filter based on a saturation method, which gives a small gain if the innovation is large enough, indicating the high likelihood of compromised measurements. The estimation error of the secure centralized filter is proved to be asymptotically upper-bounded. Moreover, a secure two-time-scale distributed filter is obtained by modifying the centralized filter and employing an estimate consensus approach. Boundedness of the estimation error of the distributed filter is proved. Numerical simulations are provided in the end to show the usefulness of the two filters.
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| 6. |
- Kim, Junsoo, et al.
(författare)
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Asymptotic Stabilization over Encrypted Data with Limited Controller Capacity and Time-varying Quantizer
- 2022
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Ingår i: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 7762-7767
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Konferensbidrag (refereegranskat)abstract
- We consider a problem of implementing dynamic controllers over encrypted data for asymptotic stabilization of closed-loop systems. Though a time-varying quantizer is used and it can be infinitesimally fine with time, a major issue is that the underlying space for encrypted messages is unavoidably finite and the controller receives a limited amount of quantized data. To resolve this issue, the proposed method takes advantage of the state matrix consisting of integers, which enables the controller to generate only lower bits of the same output without computing the upper bits. Whenever a portion of the upper bits of output has converged, the computation scope can be moved further lower, receiving only lower bits of the measurement. The quantization is scheduled and the size of the message space is predetermined from the convergence rate, so that the feedback input is restored from the outcome of the lower bits, no matter how fine quantization is performed in the end. As a consequence, asymptotic stabilization can be achieved by encrypted operation, despite the limited controller capacity.
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| 7. |
- Kim, Junsoo, et al.
(författare)
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Comparison of encrypted control approaches and tutorial on dynamic systems using Learning With Errors-based homomorphic encryption
- 2022
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Ingår i: Annual Reviews in Control. - : Elsevier BV. - 1367-5788 .- 1872-9088. ; 54, s. 200-218
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Forskningsöversikt (refereegranskat)abstract
- Encrypted control has been introduced to protect controller data by encryption at the stage of computation and communication, by performing the computation directly on encrypted data. In this article, we first review and categorize recent relevant studies on encrypted control. Approaches based on homomorphic encryption, multi-party computation, and secret sharing are introduced, compared, and then discussed with respect to computational complexity, communication load, enabled operations, security, and research directions. We proceed to discuss a current challenge in the application of homomorphic encryption to dynamic systems, where arithmetic operations other than integer addition and multiplication are limited. We also introduce a Learning With Errors based homomorphic cryptosystem called "Gentry-Sahai-Waters"scheme and discuss its benefits that allow for recursive multiplication of encrypted dynamic systems, without use of computationally expensive bootstrapping techniques.
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| 8. |
- Nekouei, E., et al.
(författare)
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A Model Randomization Approach to Statistical Parameter Privacy
- 2022
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; , s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we study a privacy filter design problem for a sequence of sensor measurements whose joint probability density function (p.d.f.) depends on a private parameter. To ensure parameter privacy, we propose a filter design framework which consists of two components: a randomizer and a nonlinear transformation. The randomizer takes the private parameter as input and randomly generates a pseudo parameter. The nonlinear mapping transforms the measurements such that the joint p.d.f. of the filter's output depends on the pseudo parameter rather than the private parameter. It also ensures that the joint p.d.f. of the filter's output belongs to the same family of distributions as that of the measurements. The design of the randomizer is formulated as an optimization problem subject to a privacy constraint, in terms of mutual information, and it is shown that the optimal randomizer is the solution of a convex optimization problem. Using information-theoretic inequalities, we show that the performance of any estimator of the private parameter, based on the output of the privacy filter, is limited by the privacy constraint. The structure of the nonlinear transformation is studied in the special cases of independent and identically distributed, Markovian, and Gauss-Markov measurements. Our results show that the privacy filter in the Gauss-Markov case can be implemented as two one-step ahead Kalman predictors and a set of minimum mean square error predictors. A numerical example on occupancy privacy in a building automation system illustrates the approach.
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| 9. |
- Nekouei, Ehsan, et al.
(författare)
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A Randomized Filtering Strategy Against Inference Attacks on Active Steering Control Systems
- 2022
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Ingår i: IEEE Transactions on Information Forensics and Security. - : Institute of Electrical and Electronics Engineers (IEEE). - 1556-6013 .- 1556-6021. ; 17, s. 16-27
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we develop a framework against inference attacks aimed at inferring the values of the controller gains of an active steering control system (ASCS). We first show that an adversary with access to the shared information by a vehicle, via a vehicular ad hoc network (VANET), can reliably infer the values of the controller gains of an ASCS. This vulnerability may expose the driver as well as the manufacturer of the ASCS to severe financial and safety risks. To protect controller gains of an ASCS against inference attacks, we propose a randomized filtering framework wherein the lateral velocity and yaw rate states of a vehicle are processed by a filter consisting of two components: a nonlinear mapping and a randomizer. The randomizer randomly generates a pair of pseudo gains which are different from the true gains of the ASCS. The nonlinear mapping performs a nonlinear transformation on the lateral velocity and yaw rate states. The nonlinear transformation is in the form of a dynamical system with a feedforward-feedback structure which allows real-time and causal implementation of the proposed privacy filter. The output of the filter is then shared via the VANET. The optimal design of randomizer is studied under a privacy constraint that determines the protection level of controller gains against inference attacks, and is in terms of mutual information. It is shown that the optimal randomizer is the solution of a convex optimization problem. By characterizing the distribution of the output of the filter, it is shown that the statistical distribution of the filter's output depends on the pseudo gains rather than the true gains. Using information-theoretic inequalities, we analyze the inference ability of an adversary in estimating the control gains based on the output of the filter. Our analysis shows that the performance of any estimator in recovering the controller gains of an ASCS based on the output of the filter is limited by the privacy constraint. The performance of the proposed privacy filter is compared with that of an additive noise privacy mechanism. Our numerical results show that the proposed privacy filter significantly outperforms the additive noise mechanism, especially in the low distortion regime.
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| 10. |
- Pirani, Mohammad, et al.
(författare)
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A Game-Theoretic Framework for Security-Aware Sensor Placement Problem in Networked Control Systems
- 2022
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 67:7, s. 3699-3706
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Tidskriftsartikel (refereegranskat)abstract
- This article studies the sensor placement problem in a leader-follower networked control system for improving its security against cyber-physical attacks. In a zero-sum game, the attacker selects f nodes of the network to attack, and the detector places f sensors to detect the presence of the attack signals. In our formulation, the attacker's objective is to have a large impact on a target node in the network while being as little visible as possible to the detector. The detector, however, seeks to maximize the visibility of the attack signals. The effects of the attack signals on both the target node and the detector node are captured via the system L-2 gain from the attack signals to the target node and deployed sensors' outputs, respectively. The equilibrium strategy of the game determines the optimal locations of the sensors. The existence of Nash equilibrium for the single-attack single-sensor case is studied when the underlying connectivity graph is a directed or an undirected tree. We show that, under the optimal sensor placement strategy, an undirected topology provides a higher security level for a networked control system compared to its corresponding directed topology. For the multiple-attack multiple-sensor case, we show that the game does not necessarily admit a Nash equilibrium and introduce a Stackelberg game approach, where the detector acts as the leader. Finally, these results are used to study the sensor placement problem in a vehicle platooning application in the presence of bias injection attacks.
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