Malleability-Resistant Encrypted Control System with Disturbance Compensation and Real-Time Attack Detection

This study proposes an encrypted PID control system with a disturbance observer (DOB) using a keyed-homomorphic encryption (KHE) scheme, aiming to achieve control performance while providing resistance to malleability-based attacks. The controller integrates a DOB with a PID structure to compensate for modeling uncertainties by estimating and canceling external disturbances. To enhance security, the system is designed to output error symbols when ciphertexts are falsified during decryption or evaluation, enabling real-time detection of malleability-based signal or parameter falsification. To validate the proposed method, we conduct stage positioning control experiments and attack detection tests using an industrial linear stage. The results show that the encrypted DOB-based PID controller outperforms a conventional encrypted PID controller in terms of tracking accuracy. Furthermore, the system successfully detects two types of malleability-based attacks: one that destabilizes the control system, and another that degrades its performance. The primary contributions of this study are: (i) the implementation of a KHE-based encrypted DOB-PID controller, (ii) the improvement of control performance under uncertainties, and (iii) the experimental demonstration of attack detection capabilities in encrypted control systems.