- Published in: Decision and Control (CDC), 2017 IEEE 56th Annual Conference on
- http://ieeexplore.ieee.org/document/8263842/
- Authors: Juhoon Back, Jihan Kim, Chanhwa Lee, Gyunghoon Park, and Hyungbo Shim
- Abstract: Zero dynamics attack is lethal to cyber-physical systems in the sense that it is stealthy and there is no way to detect it. Fortunately, if the given continuous-time physical system is of minimum phase, the effect of the attack is negligible even if it is not detected. However, the situation becomes unfavorable again if one uses digital control by sampling the sensor measurement and using the zero-order-hold for actuation because of the ‘sampling zeros’. When the continuous-time system has 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 of minimum phase), so that the cyber-physical system becomes vulnerable to ‘sampling zero dynamics attack’. In this paper, we begin with its demonstration by a few examples. Then, we present an idea to protect the system by allocating those discrete-time zeros into stable ones. This idea is realized by employing the so-called ‘generalized hold’ which replaces the zero-order-hold.
사이버 물리 시스템은 controller와 system 이 물리적으로 분리되어 있기때문에 여러가지 외부의 공격에 취약하다. 그 중 zero dynamics attack 은 시스템의 영동역학(zero dynamics)의 불안정성을 이용하여 공격하기 때문에, 그 효과가 강력하고 시스템의 오작동을 검출하는 anomaly detector 로는 검출이 불가능한 사이버 공격 형태이다. 본 논문에서는 이러한 zero dynamics attack이 sampled-data control 관점에서 매우 위험하다는 사실을 보이고, 또한 sampled-data system 에서 흔히 사용하는 zero-order hold를 generalized hold로 변경하면 discrete-time zeros의 위치를 임의로 변경할 수 있다는 사실을 이용하여 (zero dynamics attack에서 이용할 수 있는 영동역학의 불안정성을 제거함으로써) 시스템의 보안성을 확보 할 수 있음을 보였다.
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