Transitioning from Classical to Post-Quantum Security: Threat Models, Migration Strategies, Hardware Constraints, and Real-World Applications

Abstract

Classical cryptographic systems that power modern digital communication, software security, digital financial transactions, and digital sign-in and security for critical infrastructures are challenged by very fast development of quantum computer. The review explores the shift from classical to post-quantum security, and how to combine threat models for the quantum era, post-quantum cryptographic methods, migration strategies, constraints on hardware, and practical examples. It describes how Shor's algorithm can break RSA, Diffie–Hellman and elliptic-curve cryptography, and how Grover's algorithm can break the security of symmetric encryption and hash functions. Focusing on the harvest-now-decrypt-later threat, protocol downgrade attacks, side-channel leakage, and fault injection. The review discusses the different approaches lattice-based, hash-based, code-based, multivariate, and isogeny-based, making a particular focus on the standardized ones, ML-KEM, ML-DSA, and SLH-DSA. It also suggests the concept of a phased migration program – cryptographic discovery, risk assessment, transitional deployment, optimization via crypto agile infrastructures. Other hardware and implementation related topics such as memory, computation, energy, secure randomness, masking and accelerator design are also explored. Migration needs differ significantly between industries, as evidenced by the myriad of practical implementations in secure messaging, finance, telecom, IoT systems, government, healthcare and critical infrastructure. In summary, it is necessary to coordinate standardization, risk-based planning, conducting interoperability testing, implementing cryptographically secure solutions, establishing organizational governance, preparing the workforce, continuously monitoring, and designing cryptographic architectures that can evolve to address new threats and future cryptanalyses.