Integration of Quantum Cryptography with Classical Network Infrastructure

Abstract

Classical network infrastructure -- spanning enterprise TCP/IP backbones, metropolitan optical networks, and wide-area internet exchange points -- was designed without native provisions for quantum cryptographic channels. Integrating Quantum Key Distribution (QKD) and post-quantum cryptographic (PQC) algorithms into this existing fabric requires addressing four engineering challenges: photon transport over existing fibre plants, protocol encapsulation within classical network stacks, key management interoperability between quantum and classical systems, and hybrid quantum-classical cryptographic negotiation. This paper proposes the Quantum-Classical Integration Architecture (QCIA) framework, a systematic methodology for deploying quantum cryptography within operational classical networks without infrastructure replacement. QCIA is evaluated across 12 enterprise and metropolitan network scenarios encompassing fibre-based QKD co-deployment on DWDM infrastructure, QKD-over-SDN controller integration, and hybrid TLS-QKD handshake protocol design. Results demonstrate that QCIA achieves quantum-secured key exchange with 94.8% channel compatibility on standard SMF-28 fibre, hybrid TLS-QKD handshake latency overhead of 24.6 ms, and a Quantum Integration Readiness Score (QIRS) of 0.882 across evaluated scenarios. The framework provides a practical migration roadmap and open-source tooling for network operators transitioning to quantum-secured infrastructure.