<p>The primary objective of integrating the plant–control system within information security frameworks is to maintain the stability of communication processes while simultaneously enhancing the confidentiality and integrity of encrypted data. In this architecture, the control mechanism functions as an additional security layer beyond conventional encryption, enabling real-time monitoring of system dynamics and prompt detection of anomalies or malicious interventions. This layered approach significantly fortifies the overall security posture by making unauthorized access and tampering more difficult to execute. The control system operates synergistically with encryption schemes, not only ensuring consistent system performance but also increasing resilience against potential cyber threats. In this work, we introduce a novel methodology for the secure and privacy-preserving implementation of time-invariant controllers, leveraging the closed-loop plant–controller system in conjunction with the Diffie–Hellman key exchange protocol. A critical security challenge addressed is the mitigation of overflow and underflow risks within the encrypted domain, which we tackle through periodic resetting of the controller’s internal state variables. Furthermore, we propose a lightweight and computationally efficient mechanism for tamper detection of transmitted messages in environments devoid of a public key infrastructure. This mechanism relies on the establishment of shared secret keys via Diffie–Hellman exchanges combined with cryptographic hash functions to verify message integrity. The efficacy of the proposed approach is demonstrated through a detailed numerical example, and formal proofs are provided to guarantee reliable detection of any message manipulation.</p>