Practical hybrid PQC-QKD protocols with enhanced security and performance

The evolution of large-scale, fault-tolerant quantum computation necessitates the development of communication protocols which are suitably resistant to quantum-equipped adversaries. Quantum Key Distribution (QKD) constitutes one strategy for resistance, providing information-theoretic security by encoding the shared information in photonic quantum states. Alternately, Post-Quantum Cryptography (PQC) comprises a suite of classical cryptographic primitives which derive security from problems conjectured to be hard even for quantum computers. Nonetheless, both approaches face ongoing challenges. QKD requires quantum hardware which may be limited by device imperfections and by transmission losses at long distances; on the other hand, PQC implementations may be computationally expensive, and their security has not been conclusively demonstrated. In this work, we explore various hybrid schemes within a joint quantum-classical network that combine quantum and post-quantum symmetric key sharing mechanisms, detailing how each hybrid design offers a potential enhancement in security or performance. Moreover, we present straightforward and customizable methods for analyzing the security and performance of such hybrid protocols in any key distribution network. Our general approach illuminates a path forward for efficient and secure communication in joint quantum-classical networks.