Brownfield supervisory control and data acquisition environments face a migration problem that is materially different from enterprise information technology. Post-quantum cryptography must be introduced into systems that privilege safety, deterministic communications, long asset lifetimes, staged outages, vendor-certified configurations, and protocol heterogeneity. At the same time, the public standards landscape changed rapidly between 2023 and March 2026, including finalization of the NIST ML-KEM, ML-DSA, and SLH-DSA standards, publication of NIST guidance for key-encapsulation mechanisms, growth of national migration roadmaps, and active standardization of hybrid and pure post-quantum handshakes for Transport Layer Security and Internet Key Exchange. This paper develops a framework for hybrid classical-post-quantum migration in brownfield SCADA settings that is evidence-based, implementation-oriented, and explicitly staged. We distinguish coexistence from true cryptographic hybridization, quantify control-plane overhead using official algorithm sizes and current protocol drafts, and propose a conduit-first migration sequence that prioritizes gateways, remote access, management planes, trust anchors, and software-signing services before intrusive field-device replacement. To support the applied-research claim, the framework is evaluated through standards-derived protocol-overhead analysis, a representative brownfield case demonstration, explicit scoring-model parameter rationale, sensitivity analysis, phase-gate validation criteria, and a pilot evidence package. The result is a practical path for operators who must begin quantum-safe preparation now, even where endpoint-native post-quantum support remains uneven.
Brownfield supervisory control and data acquisition environments face a migration problem that is materially different from enterprise information technology. Post-quantum cryptography must be introduced into systems that privilege safety, deterministic communications, long asset lifetimes, staged outages, vendor-certified configurations, and protocol heterogeneity. At the same time, the public standards landscape changed rapidly between 2023 and March 2026, including finalization of the NIST ML-KEM, ML-DSA, and SLH-DSA standards, publication of NIST guidance for key-encapsulation mechanisms, growth of national migration roadmaps, and active standardization of hybrid and pure post-quantum handshakes for Transport Layer Security and Internet Key Exchange. This paper develops a framework for hybrid classical-post-quantum migration in brownfield SCADA settings that is evidence-based, implementation-oriented, and explicitly staged. We distinguish coexistence from true cryptographic hybridization, quantify control-plane overhead using official algorithm sizes and current protocol drafts, and propose a conduit-first migration sequence that prioritizes gateways, remote access, management planes, trust anchors, and software-signing services before intrusive field-device replacement. To support the applied-research claim, the framework is evaluated through standards-derived protocol-overhead analysis, a representative brownfield case demonstration, explicit scoring-model parameter rationale, sensitivity analysis, phase-gate validation criteria, and a pilot evidence package. The result is a practical path for operators who must begin quantum-safe preparation now, even where endpoint-native post-quantum support remains uneven.
Abstract: This study investigates quantum-safe modernization strategies for critical infrastructure by proposing a rigorous post-quantum (PQ) migration and verification framework that treats cryptographic transition as a safety-critical, multi-system engineering program rather than a routine software upgrade. The core argument is that infrastructure operators face two coupled risks: (i) cryptanalytic obsolescence of classical public-key systems under cryptographically relevant quantum computing and (ii) operational fragility introduced by large-scale cryptographic refactoring across heterogeneous assets such as industrial control systems, substation automation, telecommunications backhaul, and safety instrumentation. To address both, the framework integrates inventory-driven migration planning, hybrid-mode interoperability controls, and verification evidence that is continuously auditable across the asset lifecycle. The manuscript operationalizes verification as a chain of assurance spanning algorithm selection, protocol composition, implementation conformance, and deployment governance. Standardized PQ primitives (e.g., ML‑KEM for key establishment and ML‑DSA/SLH‑DSA for signa-tures) are used as reference baselines, with explicit attention to size and performance implications that alter network and device constraints. Real-data collection is defined as standards-backed parameter extraction, vendor/firmware artifact inspection, and protocol telemetry capture in representative environments. Results are reported as decision-facing tables and figures that quantify payload expansion, transition milestones, and published performance overheads, alongside interpretation of their operational significance for safety and resilience. Keywords: post-quantum cryptography; ML-KEM; ML-DSA; SLH-DSA; CNSA 2.0; critical infrastructure; migration governance; protocol verification; conformance testing; cryptographic agility
The impressively fast development of quantum computing is a serious threat to classical public-key cryptography, and algorithms such as Shor's and Grover's will render RSA and elliptic curve systems essentially useless as soon as a cryptanalytically relevant quantum computer becomes available. Although it is still some way off before such machines are available, the harvest-now-encrypt-later threat highlights the need for proactive defense. In response, the National Institute of Standards and Technology (NIST) published the first post-quantum cryptography standards in 2024, including ML-KEM (Kyber) for key establishment, ML-DSA (Dilithium) for digital signatures and SLH-DSA (SPHINCS+) as a stateless hash-based alternative. This paper is a summary of the evolving post-quantum landscape, starting with the standards and their underlying security and then moving on to migration policies such as CNSA 2.0 and CISA, NSA and NIST guidance. It also looks at integration patterns for important protocols such as TLS, IPsec, SSH, and code signing. A performance, interoperability and overhead evaluation methodology is presented with results showing that hybrid deployment and crypto-agile architectures make PQC adoption a viable option. The paper concludes by providing a governance-oriented roadmap, where inventory, prioritization and pilot deployments are identified as near-term actions, with open questions remaining on performance optimization, implementation security and algorithm resilience over time.
The transition to post-quantum cryptography presents enterprises with a complex systems-engineering challenge extending beyond algorithm replacement. Transport Layer Security, public key infrastructure, virtual private networks, cloud-native platforms, identity services, and machine-to-machine communications depend on interconnected cryptographic libraries, certificates, protocols, hardware modules, policies, and vendor products. This review examines crypto-agile migration to hybrid post-quantum cryptography, where classical and quantum-resistant mechanisms are combined to preserve established assurance while emerging algorithms and implementations mature. It develops a migration-oriented taxonomy covering cryptographic discovery, dependency mapping, hybrid key establishment, composite authentication, certificate lifecycle management, protocol negotiation, performance optimization, interoperability testing, and operational governance. Particular attention is given to larger keys, ciphertexts, and signatures; handshake fragmentation; certificate-chain expansion; hardware acceleration; legacy compatibility; downgrade resistance; and observability across distributed environments. The review compares migration requirements in enterprise TLS, PKI, remote-access and site-to-site VPNs, service meshes, API gateways, container platforms, serverless services, secrets systems, and multicloud infrastructures. It also analyzes staged deployment patterns, including inventory-first modernization, proxy-based termination, dual certificates, hybrid tunnels, algorithm-policy abstraction, and controlled fallback. Evaluation criteria integrate security, interoperability, latency, throughput, bandwidth, memory, certificate issuance, operational resilience, and rollback readiness. The findings indicate that successful migration depends on treating cryptography as a continuously governed enterprise capability rather than a fixed protocol configuration. The paper concludes by identifying gaps in standardization, automated discovery, cross-vendor testing, cryptographic telemetry, constrained-device support, and lifecycle evidence, providing organizations with a structured foundation for prioritized, reversible, and verifiable post-quantum transformation across heterogeneous digital services. Keywords: Crypto-Agility, Hybrid Cryptography, Post-Quantum Cryptography, Public Key Infrastructure, Quantum-Safe Migration, Transport Layer Security.
Internet public-key cryptography faces long-term risk from quantum computers, especially when traffic can be collected now and decrypted later. After the NIST post-quantum cryptography standards, the deployment task has shifted from algorithm selection to protocol migration. This paper reviews ML-KEM hybrid key exchange in TLS and SSH through a standards-first narrative review and protocol comparison. It synthesizes NIST standards, RFCs and IETF drafts, experiments, measurements, and primary deployment reports. The paper develops a deployment-readiness framework with four layers: security continuity, protocol integration, operational observability, and crypto-agility. The analysis shows hybrid key exchange represents the most feasible short-term solution, as it introduces post-quantum confidentiality without discarding existing elliptic curve security guarantees. However, hybrid deployment does not provide full post-quantum security. The review argues that readiness depends on protocol binding, implementation behavior, monitoring, and governance as much as on algorithm strength. Handshake size, middlebox compatibility, implementation safety, telemetry, authentication migration, and organizational crypto-agility determine whether migration can progress without weakening current Internet security.
Enterprises face an immediate need to protect long-lived data against harvest-now, decrypt-later threats while maintaining interoperability across layered systems. With NIST’s first post-quantum standards finalized (ML-KEM, ML-DSA, SLH-DSA) and TLS hybridization drafts defining concrete ECDHE + ML-KEM groups, adoption can begin at the TLS termination layer even before full ecosystem support for post-quantum signatures arrives (NIST, 2024; IETF, 2025). In this paper, we propose an enterprise-oriented transition framework and maturity model for hybrid TLS across email, internal API gateways, and object storage. We specify where to enforce, which hybrid groups to select, and how to prevent silent downgrade with policy pinning and negotiated-group telemetry. A controls map, risk register, and procurement/readiness checklist translate standards and drafts into auditable operational outcomes. The result is a governance-first blueprint that accelerates post-quantum readiness without requiring immediate, organization-wide cryptographic replacement.
Large-scale quantum computers threaten the public-key cryptography that protects enterprise data, communications, and digital identity. Shor's algorithm solves integer factorization and discrete logarithms in polynomial time, which would break RSA, Diffie-Hellman, and elliptic-curve schemes once a cryptographically relevant quantum computer exists. The danger is not only future. Adversaries can record encrypted traffic today and decrypt it later, a tactic known as harvest-now-decrypt-later. In August 2024 the U.S. National Institute of Standards and Technology published its first post-quantum standards: FIPS 203 (ML-KEM, derived from CRYSTALS-Kyber), FIPS 204 (ML-DSA, from CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, from SPHINCS+). This paper presents a practical migration framework for enterprises. It reviews the quantum threat and Mosca's inequality for timing the transition, summarizes the new standards with their key and signature sizes, and proposes a five-phase roadmap built on crypto-agility: discovery and inventory, risk prioritization, agility engineering, hybrid deployment, and validation. Performance trade-offs are analyzed using documented parameter sizes and illustrative TLS handshake figures. ML-KEM-768 carries a 1,184-byte public key against 64 bytes for an elliptic-curve key, while SPHINCS+ signatures can exceed 17 kilobytes. The work does not report a real deployment. It consolidates published parameters and field guidance into an actionable plan, and it highlights open challenges in certificate sizing, hardware support, and long-lived embedded systems.