2020 |
Jung Hee Cheon / Dongwoo Kim / Junsoo Kim / Seungbeom Lee / Hyungbo Shim Authenticated Computation of Control Signal from Dynamic Controllers Proceedings Article In: Proc. of 2020 IEEE 59th Conference on Decision and Control, pp. 3249-3254, IEEE, Jeju, Korea, 2020, ISBN: 978-1-7281-7447-1. Abstract | Links | BibTeX | Tags: Secure control system, Verifiable computation @inproceedings{CheonKimKimLeeShim20,Significant concerns on networked control systems are modifications on the control signals caused by a compromise on the network or the controller, since it can cause a devastating behavior or even entire failure of the system. In this paper, we present a fundamental solution to this problem by proposing a new authenticated computation that checks the matrix-vector multiplications-the main arithmetic of a controller-and verifies the updates on the states of the controller. It enables the plant-side not only to check the computation of the controller with much less computational cost than that required for the computation itself, but also to detect any modifications on the control signals. |
Junsoo Kim / Farhad Farokhi / Iman Shames / Hyungbo Shim Toward Nonlinear Dynamic Control over Encrypted Data for Infinite Time Horizon Proceedings Article In: Proc. of the 21th World Congress, IFAC, Berlin, Germany, 2020. Abstract | Links | BibTeX | Tags: Controller encryption, Privacy, Secure control system @inproceedings{KimFarokhiShamesShim20,Recent studies on encrypted control using homomorphic encryption allow secure operation by directly performing computations on encrypted data without decryption. Implementing dynamic controllers on encrypted data presents unique challenges due to limitations on the number of operations on an encrypted message. Hence, it may not be possible to perform the recursive operations for an infinite time horizon. In this note, we demonstrate that it is possible to run a dynamic controller over encrypted data for an infinite time horizon if the output of the controller can be represented as a function of a fixed number of previous inputs and outputs. The presented implementation requires encryption at both input and output of the plant. We identify a class of nonlinear systems that can accommodate the proposed implementation. The closed-loop performance can be guaranteed using the proposed encrypted controller by ensuring that quantization error is made arbitrarily small with appropriate choice of parameters. We show that the proposed method is amenable to linear systems (as a subset of the said nonlinear systems) with performance guarantees. |
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. |
List of English Publication
2020 |
Authenticated Computation of Control Signal from Dynamic Controllers Proceedings Article In: Proc. of 2020 IEEE 59th Conference on Decision and Control, pp. 3249-3254, IEEE, Jeju, Korea, 2020, ISBN: 978-1-7281-7447-1. |
Toward Nonlinear Dynamic Control over Encrypted Data for Infinite Time Horizon Proceedings Article In: Proc. of the 21th World Congress, IFAC, Berlin, Germany, 2020. |
Neutralizing zero dynamics attack on sampled-data systems via generalized holds Journal Article In: Automatica, vol. 113, pp. 108778, 2020, ISSN: 0005-1098. |