PQC Migration Without Tears: A Crypto-Agility Playbook for CISOs

Credit: MS. TECH, CC BY-ND

From board mandate to signed contracts—a practical path to quantum-safe

Every few months a board asks the same thing: Are we exposed if a future quantum computer breaks today’s encryption? The short answer is yes—for the parts of your estate that rely on public-key cryptography (the math behind TLS handshakes, VPNs, code signing, and digital certificates). Attackers can capture traffic now and store it, waiting for quantum machines powerful enough to decrypt it later. That’s the risk commonly called harvest-now, decrypt-later.

The fix is post-quantum cryptography (PQC)—new, classical (non-quantum) algorithms designed to resist both today’s attackers and tomorrow’s quantum ones. Think of PQC as drop-in replacements for the two roles public-key crypto plays everywhere:

• A key-establishment step that lets two strangers create a shared secret (today that’s usually Diffie–Hellman).

• A digital signature that proves “this software, certificate, or message genuinely came from us” (today that’s RSA or ECDSA).

• PQC gives you new building blocks for both jobs. You implement them in the same protocols, on the same networks, with the same hardware security modules—just with different math under the hood.

Here’s what PQC solves that regular crypto can’t: today’s public-key schemes are vulnerable to a specific quantum algorithm that would, in time, make factoring and discrete logs tractable at scale. Symmetric crypto (like AES) and hashes largely survive with bigger keys; public-key does not. PQC closes that gap without changing your business workflows: browsers still negotiate secure sessions; CI/CD still signs builds; your PKI still issues certificates—only now the core math is quantum-resistant.

Make it a programme, not a science experiment

Labs aren’t needed; you need governance and sequencing by running two tracks in parallel, to reduce risk while migrating.

Track A — Migrate the estate. Start where trust begins: code signing and secure boot. If your firmware chain is weak, everything is weak. Move build systems and Hardware Security Modules (HSMs) to PQC signatures, then re-sign critical artefacts as part of normal releases. Next, dual-stack your Transport Layer Security (TLS) endpoints (gateways, load balancers, service meshes) so they can negotiate both classic and PQC key exchanges. This “hybrid TLS” approach lets sessions stay secure even if one side of the handshake were ever broken. Finally, plan the roll-down: VPNs and back-haul links, internal mTLS for crown-jewel services, and re-wrapping of stored keys and archives.

Track B — Reduce long-lived exposure now. Assume some data must stay secret for years. Shorten certificate lifetimes; rotate secrets faster; prioritise links and databases with long confidentiality horizons (health, IP, state). Tighten supplier dependencies by asking vendors for PQC roadmaps and interop evidence before renewals.

Explain it so non-specialists can sign

When you brief senior leadership and the audit chair, avoid algorithm names. Instead, explain cryptography by the jobs it performs:

• Key-establishment: “We’re replacing the way two endpoints agree a shared secret.”

• Digital signatures: “We’re replacing the math behind the ‘seal’ on software, certificates, and identities.”

• Hybrid period: “For a time we’ll run both old and new in parallel; nothing breaks if one side fails.”

• Outcome: “Same services, same performance targets, but with cryptography we can defend in the 2030s.”

Treat crypto as a service, not a library scattered through apps. Centralise primitives behind an HSM or crypto service so applications call an API; when algorithms change, you upgrade once. Bake three clauses into supplier contracts: (1) a PQC delivery timeline aligned to your milestones, (2) interoperability test evidence (including hybrid TLS), and (3) a change-management plan for firmware, libraries, and certificates. This moves schedule risk off your team and onto vendors who own the knobs.

Stand up a small interop sandbox: at least one PQC-capable HSM, a TLS terminator that supports hybrid handshakes, and your main client stacks. Log cipher negotiation so you can prove what ran where. Keep an algorithm bill of materials—a simple register of which systems use which KEM/signature and where—next to your SBOM. If behaviour changes after an update, you can explain it in minutes, not days.

Budget and sequencing (what gets you the most risk reduction fastest) and why this is worth doing now

Year 1 is about prepare and prove: finish the cryptographic inventory, pilot hybrid TLS at the edge, switch your build/signing to PQC, and add PQC clauses to all new supplier contracts. Year 2 is flip and extend: roll PQC into internet-facing gateways and priority internal services; re-sign firmware trees as part of routine releases. Year 3 is drain the long tail: VPNs and back-haul links, archives re-wrapped, exceptions retired. Throughout, report in business terms: percentage of revenue served through PQC-capable edges; percentage of code artefacts re-signed; count of third-party services that have shipped PQC support.

This is not spending against a distant science project. It’s operational risk management for data with long lifetimes, using standards that are now stable and widely supported. The punchline for executives: we keep the same services and user experience, but swap the core math before it ages out. Done with discipline, PQC migration looks like any other platform upgrade—planned windows, supplier milestones, and audit-ready evidence—only with a larger strategic payoff: your encryption outlives the hype cycle.