Cyber-Physical System Security in the Age of Quantum Computing: Identifying Threats and Developing Mitigation Strategies

Cyber-Physical Systems (CPS) integrate heterogeneous hardware and software components across multi-layered architectures, enabling real-time interaction between computational elements and physical environments. The rapid evolution of quantum computing introduces a paradigm shift in the threat landscape for CPS security, as quantum algorithms — particularly Shor's algorithm — threaten to compromise widely deployed public-key cryptographic schemes such as RSA and ECC. This paper provides a structured analysis of quantum-induced threats to CPS and evaluates candidate mitigation frameworks, including Post-Quantum Cryptography (PQC) and Quantum Key Distribution (QKD). We present a taxonomy of attack scenarios organised by CPS layer, a comparative analysis of quantum-resilient defence models, and a conceptual risk-projection model illustrating how cryptographic breach probabilities may evolve as quantum hardware matures between 2025 and 2050. NOTE: All tabular data in this paper are based on conceptual simulations derived from theoretical models and existing literature; they are intended as illustrative benchmarks rather than empirically validated results. Our findings indicate that migration toward hybrid PQC architectures, combined with hardware-level security measures and regulatory modernisation, is the most pragmatic near-term strategy for CPS operators facing the quantum transition.