Composable Hybrid Quantum Security: Standards-Aligned PQC and QKD for High-Value Networks

Abstract Composable hybrid quantum security combines post-quantum cryptography (PQC) and quantum key distribution (QKD) to protect high-value networks whose threat models include long-horizon confidentiality, coordinated adversaries, and systemic dependence on shared platforms. This manuscript develops a standards-aligned governance and analytics framework that treats “hybrid” as an auditable claim with explicit scope, assumptions, and evidence—rather than as a marketing label or a single technology choice. The core argument is that resilience emerges from composability: cryptographic primitives, protocol negotiations, deployment gates, and operational monitoring must be engineered so that intermediate states remain safe, downgrade paths are bounded, and assurance can be independently reconstructed. The book integrates uncertainty-aware research design for transition planning, statistical modeling for explanation and causal assessment of control effectiveness under shared dependencies, trustworthy machine learning for predictive assurance with contestability, and scalable evidence engineering for reproducible audits and lifecycle management akin to MLOps. Outputs are specified as governance artifacts—assurance cases, evidence packets, interoperability and fallback policies, migration sequencing algorithms with rollback guarantees, and cross-entity assurance agreements—intended for practical adoption across South Asia, Europe, Africa, and the Americas without inventing datasets or citations. Keywords composable security, hybrid cryptography, post-quantum cryptography, quantum key distribution, protocol negotiation, downgrade resistance, cryptographic agility, assurance case, evidence packets, standards alignment, causal evaluation, trustworthy machine learning, auditability, interoperability, safe migration, MLOps for security, concentration risk, critical networks