On the (non-)resilience of encrypted controllers to covert attacks

2026-05-13

AI Summary

While encrypted control systems ensure data confidentiality, they remain vulnerable to covert attacks that compromise integrity. This work demonstrates that public-key homomorphic encryption, due to its inherent malleability, cannot by itself defend against such attacks—even when the adversary has no knowledge of the underlying plaintext system model. To address this limitation, we propose the first integration of verifiable computation with modern homomorphic encryption schemes, achieving asymptotic security for networked control systems without incurring additional communication overhead. By doing so, our approach overcomes the security shortcomings of purely homomorphic solutions and establishes a new paradigm for encrypted control that simultaneously guarantees both confidentiality and integrity.

Abstract

The security of networked control systems (NCS) is receiving increasing attention from both cyber-security and system-theoretic perspectives. The former focuses on classical IT security goals such as confidentiality, integrity, and availability of process data, while the latter investigates tailored attacks (and detection schemes), including covert and zero-dynamics attacks. Confidentiality in control systems can, for instance, be achieved by securely outsourcing the evaluation of the controller to third-party platforms, such as cloud services. The underlying technology enabling such secure computation often is homomorphic encryption (HE). Recent works in encrypted control have proposed modifications to underlying HE schemes to achieve not only confidentiality but also resilience to certain types of integrity attacks. While extensions in this direction are desirable in principle, we show that the integrity problem in encrypted control cannot be solved by public-key HE schemes alone due to their inherent malleability. In other words, the same homomorphisms that enable encrypted control % in the first place can be leveraged not only constructively but also destructively. More precisely, we demonstrate that NCS are vulnerable to covert attacks, even when encrypted control is employed. Remarkably, this remains possible without knowledge of an unencrypted model. Yet, resilience to such attacks can still be achieved through complementary techniques. We present an approach based on verifiable computation that integrates with modern homomorphic cryptosystems and is asymptotically secure while incurring no communication overhead.

Problem

• encrypted control
• covert attacks
• homomorphic encryption
• integrity
• networked control systems

Innovation

• homomorphic encryption
• covert attacks
• verifiable computation
• encrypted control
• integrity resilience