What a Cryptographic Inventory Captures — And Why PQC Migration Starts Here

You cannot migrate what you have not located

Every post-quantum migration starts with the same problem: most organizations do not have a full picture of the cryptography they already run. Algorithms accumulate over years — inside applications, libraries, appliances, service-to-service links, and certificates that were issued and then forgotten. Before any of it can be replaced, it has to be found.

That is what a cryptographic inventory is for. It is the discovery step of a post-quantum cryptography migration, and it is first for a simple reason: unknown cryptography is unmanaged cryptography. A key you cannot see is a key you cannot prioritize, schedule, or verify. The inventory turns that invisible surface into something you can reason about.

What a cryptographic inventory captures

A useful inventory records more than a list of algorithm names. For each place cryptography is used, it captures:

• Algorithms — which primitives are in use, and whether they are classical (for example RSA-2048, ECC P-256) or already post-quantum.
• Key sizes — the parameters that determine how much margin an algorithm actually has.
• Protocols — the transports and handshakes that carry the cryptography, since the same algorithm can be exposed very differently depending on where it sits.
• Certificate lifetimes — how long each certificate is valid, which tells you how long a given configuration will persist before it is naturally rotated.
• Where each is used — the mapping from an algorithm to the systems, services, and data that depend on it.

That last item is what makes the inventory actionable. A single weak algorithm matters very differently depending on whether it protects a short-lived internal session or long-lived data that must stay confidential for years.

Why the timeline makes this urgent, without a countdown

The reason inventory cannot wait is the shape of the migration ahead. Under the harvest now, decrypt later threat model, an adversary can capture encrypted traffic today and decrypt it later, once a sufficiently capable quantum computer exists. That means data whose confidentiality must outlive the migration window is exposed now, not at some future date.

When that quantum capability arrives is genuinely uncertain. The arrival of a cryptographically relevant quantum computer able to run Shor's algorithm is debated among researchers, and no authoritative date exists — Q-Day should be treated as open, not as a countdown. What is not uncertain is the standards timeline that governs the transition:

• NIST IR 8547 deprecates RSA-2048 and ECC P-256 in 2030 and disallows them after 2035.
• U.S. federal guidance directs that high-priority, harvest-exposed systems be migrated by the end of 2031, and all remaining systems by the end of 2035.
• FIPS 140-2 validation sunsets in September 2026, part of the broader move toward post-quantum-ready standards.

These are dated, sourced deadlines — not predictions. An inventory is what lets you map your own systems against them instead of guessing.

From inventory to a prioritized plan

An inventory on its own is a catalogue. Its value comes from what happens next — the inventory is the first of the three steps a PQC readiness assessment works through. Q-Shield takes the inventory and scores quantum risk on five axes (its five-axis QRS), so that the highest-risk, longest-lived secrets rise to the top of the queue rather than being migrated in whatever order they happen to be discovered.

From there, Q-Shield produces a NIST-aligned migration roadmap toward ML-KEM, the key-establishment mechanism standardized as FIPS 203 and published by NIST in August 2024. Where a clean cut-over is not yet appropriate, the roadmap can specify a hybrid ECDH + ML-KEM key exchange, so classical and post-quantum protection run together during the transition. ML-KEM-768 sits at NIST security category 3 and is built on the module-learning-with-errors problem with fully public parameters.

The takeaway

Post-quantum migration is a sequencing problem before it is a cryptography problem. The first move is not to pick an algorithm — it is to find every place you already use one. A cryptographic inventory that captures algorithms, key sizes, protocols, certificate lifetimes, and where each is used gives you the map. Q-Shield's role is to turn that map into a scored, NIST-aligned plan you can actually work through.