2020 |
Jihan Kim / Juhoon Back / Gyunghoon Park / Chanhwa Lee / Hyungbo Shim / Petros G. Voulgaris Neutralizing zero dynamics attack on sampled-data systems via generalized holds Journal Article In: Automatica, vol. 113, pp. 108778, 2020, ISSN: 0005-1098. Abstract | Links | BibTeX | Tags: Cyber-physical system, Sampled-data control system, Secure control system, System security, Zero-dynamics @article{Kim20,Zero dynamics attacks can be lethal to cyber–physical systems because they can be harmful to physical plants and impossible to detect. Fortunately, if the given continuous-time physical system is minimum phase, the attack is not so effective even if it cannot be detected. However, the situation can become unfavorable if one uses digital control by sampling the sensor measurement and using a zero-order hold for actuation because of the ‘sampling zeros.’ When the continuous-time system has a relative degree greater than two and the sampling period is small, the sampled-data system must have unstable zeros (even if the continuous-time system is minimum phase), so that the cyber–physical system becomes vulnerable to ‘sampling zero dynamics attack.’ In this paper, we present an idea to neutralize the zero dynamics attack for single-input and single-output sampled-data systems by shifting the unstable discrete-time zeros into stable ones. This idea is realized by employing the so-called ‘generalized hold’ which replaces a standard zero-order hold. It is shown that, under mild assumptions, a generalized hold exists which places the discrete-time zeros at desired positions. Furthermore, we formulate the design problem as an optimization problem whose performance index is related to the inter-sample behavior of the physical plant, and propose an optimal gain which alleviates the performance degradation caused by generalized hold as much as possible. |
2019 |
Jihan Kim / Hyungbo Shim A Countermeasure against Zero-dynamics Sensor Attack via Generalized Hold Feedback Proceedings Article In: Proc. of the SICE Annual Conference 2019, pp. 663-668, SICE, Hiroshima, Japan, 2019. Abstract | Links | BibTeX | Tags: Cyber-physical system, Generalized hold, Resilient control system, Sampled-data control system @inproceedings{KimShim19,The zero-dynamics attack is well-known for its lethality and stealthiness. This infamous attack has usually been studied as a type of actuator attack. In this paper, however, we focus on the zero-dynamics attack having a form of a sensor attack. In particular, when the system monitors abnormal behavior of the plant using the anomaly detector, an undetectable sensor attack can be generated, which deceives the anomaly detector. It is noticed that this sensor attack is not so effective when the plant is stable even if the attack is still undetectable. In view of this point, we propose to reexamine the so-called ‘generalized hold’ as a countermeasure against the undetectable sensor attack. Specifically, using the fact that the output feedback composed of the ‘generalized hold’ can stabilize the unstable systems by selecting an appropriate hold function, we show that the plant can be safe from the undetectable sensor attack. |
Chanhwa Lee / Hyungbo Shim / Yongsoon Eun On Redundant Observability: From Security Index to Attack Detection and Resilient State Estimation Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 2, pp. 775-782, 2019. Abstract | Links | BibTeX | Tags: Attack detection, Cyber-physical system, Resilient state estimation @article{LeeShimEun19,The security of control systems under sensor attacks is investigated. Redundant observability is introduced, explaining existing security notions including the security index, attack detectability, and observability under attacks. Equivalent conditions between redundant observability and existing notions are presented. Based on a bank of partial observers utilizing Kalman decomposition and a decoder exploiting redundancy, an estimator design algorithm is proposed enhancing the resilience of control systems. This scheme substantially improves computational efficiency utilizing far less memory. |
Junsoo Kim / Chanhwa Lee / Hyungbo Shim / Yongsoon Eun / Jin Heon Seo Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems having Redundant Sensors Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 3, pp. 1162-1169, 2019, ISBN: 0018-9286. Abstract | Links | BibTeX | Tags: Attack detection, Cyber-physical system, Resilient state estimation @article{KimLeeShimEunSeo19,This paper presents a detection algorithm for sensor attacks and a resilient state estimation scheme for a class of uniformly observable nonlinear systems. An adversary is supposed to corrupt a subset of sensors with the possibly unbounded signals, while the system has sensor redundancy. We design an individual high-gain observer for each measurement output so that only the observable portion of the system state is obtained. Then, a nonlinear error correcting problem is solved by collecting all the information from those partial observers and exploiting redundancy. A computationally efficient, on-line monitoring scheme is presented for attack detection. Based on the attack detection scheme, an algorithm for resilient state estimation is provided. The simulation results demonstrate the effectiveness of the proposed algorithm. |
2016 |
Gyunghoon Park / Hyungbo Shim / Chanhwa Lee / Yongsoon Eun / Karl H. Johansson When Adversary Encounters Uncertain Cyber-physical Systems: Robust Zero-dynamics Attack with Disclosure Resources Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5085-5090, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Cyber-physical system, Uncertain systems @inproceedings{ParkShimLeeEunJohansson16,In this paper we address the problem of designing a robust stealthy attack for adversaries to compromise an uncertain cyber-physical system without being detected. We first re-interpret the zero-dynamics attack based on the normal form representation. Then, a new alternative zero dynamics attack is presented for uncertain systems. This alternative employs a disturbance observer and does not require exact system knowledge in order to remain stealthy. The proposed robust zero-dynamics attack needs a nominal model of the system and, in addition, utilizes the input and output signals of the system. The proposed attack illustrates how the adversary is able to use disclosure resources instead of exact model knowledge. A simulation result with a hydro-turbine power system is presented to verify the attack performance. |
Junsoo Kim / Chanhwa Lee / Hyungbo Shim / Jung Hee Cheon / Andrey Kim / Miran Kim / Yongsoo Song Encrypting Controller using Fully Homomorphic Encryption for Security of Cyber-Physical Systems Proceedings Article In: Proc. of 6th IFAC Workshop on Distributed Estimation and Control in Networked Systems, pp. 175-180, Tokyo, Japan, 2016. Abstract | Links | BibTeX | Tags: Controller encryption, Cyber-physical system, Homomorphic encryption, Security @inproceedings{KimLeeShimCheonKimKimSong16,In order to enhance security of cyber-physical systems, it is important to protect the signals from sensors to the controller, and from the controller to the actuator, because the attackers often steal and compromise those signals. One immediate solution could be encrypting the signals, but in order to perform computation in the controller, they should be decrypted before computation and encrypted again after computation. For this, the controller keeps the secret key, which in turn increases vulnerability from the attacker. In this paper, we introduce the fully homomorphic encryption (FHE), which is an advanced cryptography that has enabled arithmetic operations directly on the encrypted variables without decryption. However, this also introduces several new issues that have not been studied for conventional controllers. Most of all, an encrypted variable has a finite lifespan, which decreases as an arithmetic operation is performed on it. Our solution is to run multiple controllers, and orchestrate them systematically. Also, in order to slow down the decrease of the lifespan, a tree-based computation of sequential matrix multiplication is introduced. We finally demonstrate the effectiveness of the proposed algorithm with quadruple water tank example. |
List of English Publication
2020 |
Neutralizing zero dynamics attack on sampled-data systems via generalized holds Journal Article In: Automatica, vol. 113, pp. 108778, 2020, ISSN: 0005-1098. |
2019 |
A Countermeasure against Zero-dynamics Sensor Attack via Generalized Hold Feedback Proceedings Article In: Proc. of the SICE Annual Conference 2019, pp. 663-668, SICE, Hiroshima, Japan, 2019. |
On Redundant Observability: From Security Index to Attack Detection and Resilient State Estimation Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 2, pp. 775-782, 2019. |
Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems having Redundant Sensors Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 3, pp. 1162-1169, 2019, ISBN: 0018-9286. |
2016 |
When Adversary Encounters Uncertain Cyber-physical Systems: Robust Zero-dynamics Attack with Disclosure Resources Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5085-5090, IEEE, Las Vegas, NV, USA, 2016. |
Encrypting Controller using Fully Homomorphic Encryption for Security of Cyber-Physical Systems Proceedings Article In: Proc. of 6th IFAC Workshop on Distributed Estimation and Control in Networked Systems, pp. 175-180, Tokyo, Japan, 2016. |