Cryptographic Inventory as the Denominator for Post-Quantum Migration Prioritization
Post-quantum cryptography migration is often framed as a standards-adoption problem: replace quantum-vulnerable public-key algorithms with newly standardized algorithms. That framing is incomplete. This paper synthesizes NIST FIPS standards, NCCoE migration workstreams, NIST crypto-agility guidance, and CISA-NSA-NIST quantum-readiness guidance to argue that cryptographic inventory is the denominator for migration prioritization. The evidence shows that ML-KEM, ML-DSA, and SLH-DSA define the algorithmic destination, while discovery, inventory, vendor engagement, interoperability testing, and crypto agility define whether an organization can rank and execute the transition. The proposed contribution is an inventory-first prioritization model: classify cryptographic uses by secrecy lifetime, asset criticality, algorithm role, vendor control, and replacement feasibility before scheduling migration waves. This model separates algorithm readiness from organizational readiness and avoids the false precision of treating all RSA, ECDH, and ECDSA dependencies as one backlog.
Introduction
NIST released the first three principal post-quantum cryptography standards in 2024 and states that organizations should begin applying them now [[cite:nist_pqc_project,nist_pqc_overview]]. The standards define usable cryptographic primitives, but they do not automatically tell an organization which system to migrate first.
This distinction matters because quantum-readiness guidance repeatedly starts with discovery and inventory. The joint CISA, NSA, and NIST factsheet urges roadmaps, inventories, risk assessment, and vendor engagement, and explicitly links long secrecy lifetime to harvest-now-decrypt-later risk [[cite:quantum_readiness_factsheet,nsa_prepare_now]].
The research question is: how should organizations use cryptographic inventory to prioritize post-quantum migration after the NIST FIPS standards are available? The contribution is an inventory-first prioritization model that treats standards as the destination and inventory fields as the denominator for risk ordering.
Method
I used a conceptual-synthesis method over official standards, agency guidance, and NCCoE migration documentation. Sources were included when they defined a PQC target algorithm, migration workstream, inventory requirement, crypto-agility constraint, or risk-framework mapping. Vendor engineering examples were screened but excluded from the final references to keep the synthesis grounded in neutral sources.
Priority(u) = f( secrecy_lifetime, asset_criticality, algorithm_role, exposure, vendor_control, replacement_feasibility )
Equation (1) is a queue heuristic, not a cryptographic security proof. The unit u is a cryptographic use: a protocol endpoint, certificate chain, firmware signer, service dependency, key-establishment flow, or product feature. The model ranks uses before projects so that a single application can contain both urgent and routine migration targets.
Results
Finding 1: standards readiness and organization readiness are different states. FIPS 203, 204, and 205 define ML-KEM, ML-DSA, and SLH-DSA as standardized primitives [[cite:fips203,fips204,fips205]]. But NCCoE migration material emphasizes discovery, interoperability testing, and risk prioritization before deployment [[cite:nccoe_migration,sp1800_38]].
Finding 2: inventory is the denominator. The quantum-readiness factsheet says an inventory of quantum-vulnerable technology and criticality enables risk assessment and prioritization, while NCCoE describes cryptographic discovery as learning where and how cryptography protects important data and systems [[cite:quantum_readiness_factsheet,cswp48]]. Without an inventory, a migration roadmap is a list of aspirations rather than a schedulable queue.
Finding 3: crypto agility is the execution capability. CSWP 39 defines cryptographic agility as the ability to replace and adapt algorithms in protocols, applications, software, hardware, firmware, and infrastructure while preserving ongoing operations [[cite:cswp39]]. Inventory identifies what to change; agility determines whether change is technically and operationally possible.
Finding 4: vendor engagement is part of the inventory. The factsheet tells organizations to engage vendors on quantum-readiness roadmaps and to understand how cloud, commercial off-the-shelf, and custom products will migrate [[cite:quantum_readiness_factsheet]]. A useful inventory therefore records ownership and vendor dependency, not just algorithm names.
Inventory-First Prioritization Model
The proposed model has three passes. Pass one discovers cryptographic uses and tags their algorithm role. Pass two adds risk context: secrecy lifetime, asset criticality, exposure, and business owner. Pass three adds execution context: vendor control, protocol compatibility, interoperability testing need, and rollback path. Only after pass three should migration waves be committed.
This model also clarifies the role of CNSA and other policy requirements. NSA materials are particularly important for National Security Systems, but the more general lesson is transferable: policies can set target algorithm suites, while inventories determine which concrete systems must move and in what order [[cite:nsa_pq_resources,nsa_prepare_now]].
Discussion
The strongest implication is that post-quantum migration cannot be managed as a single project called "replace RSA." RSA, ECDH, and ECDSA appear in transport, identity, update signing, device firmware, databases, backups, and vendor products. The same algorithm family can imply different urgency depending on secrecy lifetime, trust boundary, and replacement control.
A second implication is that crypto agility should be measured. Organizations can track the percentage of cryptographic uses with a known owner, known algorithm role, known vendor roadmap, tested PQC path, and rollback plan. These metrics are closer to migration readiness than counting how many systems mention RSA in a scan result [[cite:cswp39,nccoe_migration]].
The paper has limits. It is a conceptual synthesis rather than a measured benchmark. It uses U.S. official guidance as the main evidence base, so organizations in other jurisdictions should compare local requirements. It also does not choose parameter sets for individual protocols; that decision belongs to implementers following the relevant standards and product guidance.
Conclusion
The post-quantum migration problem is not solved when standards exist. Standards define the destination; cryptographic inventory defines the denominator; crypto agility defines execution capacity. Organizations that treat inventory as a first-class artifact can rank migration work by real risk and feasibility instead of treating every public-key dependency as an undifferentiated backlog item.