BB84 and E91 protocol mechanics, channel loss models, trusted node architectures, and operational maturity assessment.
Physics-based key distribution versus computational security. Key areas include: BB84 with decoy states: single-photon sources, basis reconciliation, and privacy amplification; Continuous-variable QKD (CV-QKD): homodyne/heterodyne detection, Gaussian modulation, and composable security proofs; Measurement-device-independent QKD (MDI-QKD) and twin-field QKD: removing detector side-channel attacks.
From point-to-point links to metropolitan and wide-area networks. Key areas include: Trusted node relay networks: key management, node compromise models, and the EuroQCI architecture; MDI mesh topologies: untrusted relay nodes and star/ring configurations; Satellite QKD: LEO downlinks (Micius experiment), daylight operation constraints, and defence implications.
When each approach fits and when it does not. Key areas include: Information-theoretic security versus computational hardness: what QKD guarantees that PQC cannot; Practical limitations: distance constraints (typically under 100 km without repeaters), key rate throughput, and hardware cost; QKD for high-value point-to-point links: nuclear command and control, embassy networks, SCIF interconnects.
Evaluating QKD for your defence environment. Key areas include: Vendor landscape: capability comparison across commercial QKD providers covering hardware maturity, key rate performance, and integration options; Procurement considerations: NCSC and BSI guidance on QKD deployment in government networks.
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