Control-theoretic Approach to Malleability Cancellation by Attacked Signal Normalization

In this study, we propose a novel attack for encrypted control systems along with a cancellation method for the attacks. The attacks assign the poles of closed-loop systems by utilizing the malleability of homomorphic encryption schemes used in encrypted control systems. Additionally, a condition of destabilization by the attacks is provided under the assumption that adversaries are aware of the homomorphic encryption scheme that is being used. The proposed method is applicable for encrypted control systems with partially or fully homomorphic encryption schemes, and completely removes influence of certain type of attacks with obfuscated controller gain, which is obtained by QR decomposition. The validity of the proposed method is examined through a numerical simulation. The results confirm that the proposed method is effective in canceling the malleability of encrypted control systems. Copyright (C) 2019. The Authors. Published by Elsevier Ltd. All rights reserved.