2022 |
Hyungbo Shim / Juhoon Back / Yongsoon Eun / Gyunghoon Park / Jihan Kim Zero-dynamics Attack, Variations, and Countermeasures Book Chapter In: Hideaki Ishii; Quanyan Zhu (Ed.): Security and Resilience of Control Systems, vol. 489, Chapter 2, pp. 31–61, Springer Cham, 1, 2022, ISBN: 978-3-030-83236-0. Abstract | Links | BibTeX | Tags: Cyber-physical systems, Security, Zero-dynamics @inbook{nokey, This chapter presents an overview of actuator attacks that exploit zero dynamics, and countermeasures against them. First, zero-dynamics attack is reintroduced based on a canonical representation called normal form. Then it is shown that the target dynamic system is at elevated risk if the associated zero dynamics is unstable. From there on, several questions are raised in series to ensure when the target system is immune to an attack of this kind. The first question is: Is the target system secure from zero-dynamics attack if it does not have any unstable zeros? An answer provided for this question is: No, the target system may still be at risk due to another attack surface emerging in the process of implementation. This is followed by a series of questions, and in the course of providing answers, variants of the classic zero-dynamics attack are presented, from which the vulnerability of the target system is explored in depth. In the end, countermeasures are proposed to render the attack ineffective. Because it is known that zero dynamics in continuous-time systems cannot be modified by feedback, the main idea of the countermeasure is to relocate any unstable zero to a stable region in the stage of digital implementation through modified digital samplers and holders. Adversaries can still attack actuators, but due to the relocated zeros, they are of little use in damaging the target system. |
2016 |
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. |
2015 |
Chanhwa Lee / Hyungbo Shim / Yongsoon Eun Secure and Robust State Estimation under Sensor Attacks, Measurement Noises, and Process Disturbances: Observer-Based Combinatorial Approach Proceedings Article In: Proc. of 2015 European Control Conference (ECC), pp. 1866-1871, IEEE, Linz, Austria, 2015. Abstract | Links | BibTeX | Tags: Continuous-time system, Security @inproceedings{LeeShimEun15, This paper presents a secure and robust state estimation scheme for continuous-time linear dynamical systems. The method is secure in that it correctly estimates the states under sensor attacks by exploiting sensing redundancy, and it is robust in that it guarantees a bounded estimation error despite measurement noises and process disturbances. In this method, an individual Luenberger observer (of possibly smaller size) is designed from each sensor. Then, the state estimates from each of the observers are combined through a scheme motivated by error correction techniques, which results in estimation resiliency against sensor attacks under a mild condition on the system observability. Moreover, in the state estimates combining stage, our method reduces the search space of a minimization problem to a finite set, which substantially reduces the required computational effort. |
List of English Publication
2022 |
Zero-dynamics Attack, Variations, and Countermeasures Book Chapter In: Hideaki Ishii; Quanyan Zhu (Ed.): Security and Resilience of Control Systems, vol. 489, Chapter 2, pp. 31–61, Springer Cham, 1, 2022, ISBN: 978-3-030-83236-0. |
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. |
2015 |
Secure and Robust State Estimation under Sensor Attacks, Measurement Noises, and Process Disturbances: Observer-Based Combinatorial Approach Proceedings Article In: Proc. of 2015 European Control Conference (ECC), pp. 1866-1871, IEEE, Linz, Austria, 2015. |