Purpose – This study develops and empirically evaluates a Quantum Exposure Index (QEI) for characterizing quantum-related exposure observable from public-sector Transport Layer Security (TLS) infrastructures and supporting post-quantum migration prioritization. Methods – The framework integrates TLS protocol version, certificate public-key algorithm, classical key-strength equivalence, and Perfect Forward Secrecy into a normalized composite index. Component weights were derived through the Analytical Hierarchy Process, while non-intrusive TLS measurements from publicly accessible government infrastructures provided the empirical inputs. Sensitivity and sector-level analyses were conducted to examine the robustness and interpretability of the resulting exposure profiles. Findings – The evaluated infrastructures remain dependent on classical public-key cryptography and therefore retain exposure to future quantum-capable adversaries despite widespread adoption of modern TLS configurations and forward secrecy. The analysis further shows that cryptographic key strength and protocol configuration differentiate exposure profiles, whereas the continued reliance on quantum-vulnerable public-key primitives establishes a common exposure baseline. Classification outcomes are sensitive to interpretive thresholds, reinforcing the importance of continuous index values over categorical labels. Research Implications – The QEI provides a reproducible infrastructure-level baseline for prioritizing cryptographic inventories, monitoring migration progress, and supporting evidence-based post-quantum transition planning. Originality – This study combines operational TLS measurement, standardized cryptographic-strength mapping, and multicriteria weighting within a unified quantitative framework for assessing observable quantum exposure in public-sector infrastructures.
Purpose – This study develops and empirically evaluates a Quantum Exposure Index (QEI) for characterizing quantum-related exposure observable from public-sector Transport Layer Security (TLS) infrastructures and supporting post-quantum migration prioritization. Methods – The framework integrates TLS protocol version, certificate public-key algorithm, classical key-strength equivalence, and Perfect Forward Secrecy into a normalized composite index. Component weights were derived through the Analytical Hierarchy Process, while non-intrusive TLS measurements from publicly accessible government infrastructures provided the empirical inputs. Sensitivity and sector-level analyses were conducted to examine the robustness and interpretability of the resulting exposure profiles. Findings – The evaluated infrastructures remain dependent on classical public-key cryptography and therefore retain exposure to future quantum-capable adversaries despite widespread adoption of modern TLS configurations and forward secrecy. The analysis further shows that cryptographic key strength and protocol configuration differentiate exposure profiles, whereas the continued reliance on quantum-vulnerable public-key primitives establishes a common exposure baseline. Classification outcomes are sensitive to interpretive thresholds, reinforcing the importance of continuous index values over categorical labels. Research Implications – The QEI provides a reproducible infrastructure-level baseline for prioritizing cryptographic inventories, monitoring migration progress, and supporting evidence-based post-quantum transition planning. Originality – This study combines operational TLS measurement, standardized cryptographic-strength mapping, and multicriteria weighting within a unified quantitative framework for assessing observable quantum exposure in public-sector infrastructures.
The emergence of quantum computing presents a fundamental challenge to the security of current Internet communication systems. Transport Layer Security (TLS), which forms the backbone of secure web communication, predominantly relies on classical public-key cryptographic algorithms such as RSA and elliptic curve cryptography (ECC), both of which are susceptible to quantum attacks. This paper conducts a large scale empirical evaluation of post-quantum readiness across 32,011 domains, with a primary focus on real-world TLS deployments across diverse sectors by analysing negotiated TLS parameters, including protocol versions, cipher suites, key exchange mechanisms, and certificates. The results indicate that while modern protocols like TLS 1.3 and QUIC are gaining adoption, 15.70% of domains especially in critical sectors such as banking and government still rely on TLS 1.2. Furthermore, 49.3% of domains support hybrid post-quantum key exchange mechanisms (e.g., MLKEM768 with X25519), whereas 50.7% continue to use classical key exchange, reflecting partial transition. Notably, 0% adoption of hybrid post-quantum certificates was observed, leaving the authentication layer vulnerable to quantum-enabled attacks such as certificate forgery. The findings reveal uneven adoption of post-quantum mechanisms across sectors, where technology driven platforms are advancing more rapidly than legacy-dependent infrastructures. Overall, the study highlights that achieving complete quantum resilience requires a coordinated transition not only in key exchange mechanisms but also in certificate infrastructures. Without such comprehensive migration, Internet communication systems remain vulnerable to long-term threats, including Harvest-Now-Decrypt-Later (HNDL) attacks.
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.
Enterprise wide-area networks (WANs) use quantum-vulnerable public-key cryptography to authenticate peers and establish keys for Internet Protocol Security (IPsec), Transport Layer Security (TLS), and software-defined WAN services. Harvest-now, decrypt-later collection already threatens data whose protection lifetime may exceed the time needed to migrate, while a future cryptographically relevant quantum computer would also endanger certificates and other authentication dependencies. Post-quantum standards and government directives now define algorithms and transition milestones, but they do not tell an enterprise which WAN services to migrate first or what evidence is sufficient for deployment. This paper proposes a vendor-neutral framework that separates exposure priority, migration readiness, and evidence confidence, and maps those outputs to staged security, operational, and governance gates. It also defines a complete evaluation design for classical and ML-KEM hybrid key establishment in TLS 1.3 and IKEv2/IPsec. The retained artifact is narrower: it contains author-reported aggregate TLS p50, p95, and p99 latencies at configured loss settings of 0%, 1%, 3%, and 5%, an arithmetic checker, and limited environment and MTU/MSS notes. At those settings, the TLS-H minus TLS-C p95 differences are 0.00, 0.16, 0.38, and 0.63 ms, corresponding to 0.00%, 1.32%, 3.07%, and 5.00% relative to TLS-C. These values are descriptive aggregate observations, not inferential results, because per-trial data, sample counts, original captures, and timestamped logs were not retained. Protocol-size and MTU/MSS calculations are reported separately from measured behavior, and unsupported IKE, resource, throughput, retransmission, and downgrade outcomes are excluded.
Post-quantum cryptography (PQC) is becoming an important component of long-term trust in Internet-facing infrastructure. Publicly observable PQC support provides evidence of externally visible deployment, but does not necessarily reflect the overall progress of an organisation's post-quantum migration. This distinction matters when observable deployment is used as an indicator of organisational readiness or progress towards migration deadlines. We present a measurement study of observable PQC deployment across 4,665 UK organisations spanning ten sectors. We measure post-quantum key-exchange support across HTTPS and SMTP STARTTLS endpoints, attribute reachable endpoints to their underlying infrastructure providers where possible, and statistically examine protocol-, sector-, and provider-level deployment patterns. Among reachable endpoints, 44.0\% of HTTPS services supported at least one evaluated PQC key-exchange group, compared with 6.4\% of SMTP services. Among organisations reachable over both protocols, HTTPS support was significantly more common than SMTP support (matched odds ratio 16.89). Although deployment varied across sectors, infrastructure provider identity was substantially more predictive than organisational sector, and observable deployment was highly concentrated among a small number of providers. Only 144 organisations supported PQC across both web and email infrastructure, highlighting an uneven and fragmented migration landscape. No post-quantum certificate signatures were observed across the measured endpoints. These findings show that observable PQC deployment is currently shaped predominantly by infrastructure-provider deployment decisions and should not be interpreted as a complete measure of organisational migration readiness.
Enterprise infrastructure operators face a critical challenge in prioritizing post-quantum migration, as quantum-related risk is not uniformly distributed across data in transit, in use, and at rest. Existing assessments rely on system-level evaluations or protocol-specific analyses, which do not capture the heterogeneity of exposure across infrastructure layers. This paper extends the Quantum-Adjusted Risk Scoring (QARS) model introduced in into an evidence-based, layer-specific framework that evaluates in-transit, in-use, and at-rest data separately. QARS applies a unified five-factor scoring framework separately to each data state and introduces a quantum-vulnerability attenuation mechanism grounded in Grover-bounded residual security that prevents overstating urgency for non-Shor-vulnerable symmetric protection. Observable host-level evidence determines the binary and ratio descriptors used by the model, while the fixed affine mapping coefficients are treated as transparent semi-quantitative calibration parameters. These coefficients are documented separately and subjected to coefficient-level sensitivity analysis to evaluate whether the reported layer ordering depends on their nominal values. The model is demonstrated through an illustrative controlled experiment using real infrastructure observations. Strengthening storage protection reduces the aggregate system risk from 0.707 (high) to 0.414 (moderate), a 41.5% reduction. However, the maximum-layer score remains high (0.657), indicating that the transport layer continues to dominate migration urgency. Sensitivity analysis confirms that the dominance of the transport layer is stable under wide perturbations of the calibration parameters. These findings demonstrate that risk reduction in one layer does not eliminate overall exposure but shifts the dominant vulnerability. By distinguishing between overall system posture and the most critical remediation priority, QARS supports infrastructure operators in identifying high-risk components and planning structured, evidence-based post-quantum migration.
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