PQC Signatures for Code & Firmware Signing (and Why Timestamping Matters)

Last updated: October 22, 2026 | Affiliate Disclosure

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Code signing and firmware signing are where post‑quantum cryptography becomes very real, very quickly – not because “quantum is here tomorrow,” but because signed artifacts often live for years. Bootloaders, update mechanisms, device fleets, offline installers, archived releases, and air‑gapped verification environments all tend to outlast the crypto assumptions they were designed with.

That long lifetime creates two practical requirements:

  • you need a credible path from classical signatures to post‑quantum signatures, and
  • you need a way to keep signatures verifiable over time, which is where timestamping becomes more than a compliance checkbox.

This guide focuses on signing systems (not general PKI, not TLS): how to think about PQC signatures for code/firmware, what breaks in real pipelines, and how timestamping fits into the story.

What “PQC signatures for code/firmware” actually means

When people say “PQC signatures,” they can mean several different things. For code and firmware signing, the core meaning is:

  • You produce a digital signature over a software artifact (binary, package, firmware image, container, manifest).
  • Verifiers (devices, OS loaders, update agents, security tooling) use a public key / certificate chain to validate that signature.
  • A “PQC transition” means the signature algorithm and ecosystem must evolve from RSA/ECDSA to post‑quantum options without breaking the verification population.

For this guide, the relevant standardized post‑quantum signature algorithms are:

  • ML‑DSA (FIPS 204)
  • SLH‑DSA (FIPS 205)
  • LMS and XMSS (NIST SP 800‑208; hash‑based signatures)

The “boring but important” fact: code signing is a verifier problem

In signing systems, the signing side is usually easier to update than the verifying side.

You can upgrade a CI pipeline faster than you can upgrade:

  • millions of deployed devices,
  • offline verification tools in regulated environments,
  • embedded boot ROM constraints,
  • third‑party scanning and allowlisting systems,
  • customer procurement requirements.

So the right mental model is:

Code/firmware PQC isn’t “can we sign with ML‑DSA?”
It’s “can every verifier we care about validate what we produce?”

This is why many organizations treat PQC signing as a multi‑year transition with controlled islands of adoption.

What standards and requirements are driving this in 2026

NIST has standardized PQC signature algorithms

NIST approved PQC signature standards as federal standards:

  • FIPS 204: ML‑DSA
  • FIPS 205: SLH‑DSA

Announcement (Aug 2024):
https://www.nist.gov/news-events/news/2024/08/announcing-approval-three-federal-information-processing-standards-fips

CNSA 2.0 makes a specific stance on signing algorithms (important nuance)

For National Security Systems (NSS) contexts:

  • CNSA 2.0 specifies ML‑DSA‑87 for digital signatures at all classification levels.
  • CNSA 2.0 allows LMS and XMSS for firmware/software signing use cases.
  • CNSA 2.0 explicitly states SLH‑DSA is not approved for any NSS use, even though it is standardized by NIST.

Primary source: NSA CNSA Suite 2.0 FAQ (Dec 2024, v2.1)
https://media.defense.gov/2022/Sep/07/2003071836/-1/-1/0/CSI_CNSA_2.0_FAQ_.PDF

Practical takeaway: if you sell into NSS-adjacent environments, “we support FIPS 205” is not the same as “we meet CNSA 2.0 expectations.”

What changes when you move to PQC signatures (real pipeline impacts)

1) Signature and key sizes change operational assumptions

PQC signature systems often deal with kilobyte-scale signatures and keys.

A concrete example from FIPS 204:

This matters because code signing ecosystems are full of “small signature” assumptions:

  • fixed-size fields in tooling and metadata stores,
  • memory constraints in embedded validators,
  • message size constraints in update protocols,
  • logging and telemetry pipelines that were never designed for multi‑KB signature blobs.

2) Tooling support arrives unevenly

Signing involves:

  • build tooling,
  • key custody (HSM/KMS),
  • signing services,
  • timestamping services,
  • artifact formats,
  • and verification stacks.

All of those layers need to support whatever you adopt. In practice, migration readiness is usually gated by verifiers (especially embedded/firmware).

3) The “trust anchor” problem becomes more visible

Even when you change signature algorithms, you still need to answer:

  • what roots/intermediates do verifiers trust?
  • how are trust stores updated?
  • how do you rotate signing certificates and keys?
  • what happens when a CA/intermediate is distrusted or a key is compromised?

PQC doesn’t remove those questions; it makes them more time-sensitive because you’re planning change anyway.

A practical roadmap: migrating signing systems without breaking verification

Step 1: Inventory what you sign (and who verifies it)

Create a list of “signed things” and “verification populations.”

At minimum, capture:

  • artifact type (firmware image, installer, package, container, manifest)
  • signing mechanism (which tool/service)
  • key custody (HSM-backed, KMS, local)
  • verifier types (bootloader, OS, update agent, customer tooling, offline scanners)
  • updateability of verifiers (easy, hard, impossible)
  • required verification lifetime (months vs decades)

This is the most important step because it tells you where PQC adoption is feasible first.

Step 2: Identify “can’t update verifiers” constraints early

Firmware verifiers are often constrained by:

  • ROM code,
  • strict size limits,
  • limited crypto library support,
  • long replacement cycles.

Those constraints often determine whether you can deploy a PQC signature scheme in the near term, or whether you need a transition approach that keeps legacy verification working.

Step 3: Choose transition patterns that match your verifier reality

Common transition patterns in signing systems include:

  • Parallel signing pipelines for different product lines (new devices verify PQ signatures; older devices remain on classical).
  • Controlled internal PQC adoption first (e.g., internal firmware signing validation or internal software distribution where you own verifiers).
  • Dual signatures / multiple signature containers where an artifact can carry more than one signature during transition periods (when the artifact format and verification ecosystem support it).

The key is not the pattern name; it’s aligning the pattern to what your verifiers can handle without outages.

Step 4: Design for key compromise and revocation events

For code/firmware signing, compromise response is not hypothetical.

A serious plan includes:

  • how to revoke/denylist a compromised signing key
  • how to roll forward to a new key/cert
  • how devices obtain updated trust/denylist data
  • how quickly you can ship an emergency re-signed update

This is exactly where timestamping and evidence retention become operationally important (see below).

Where timestamping fits (and what it does – and does not – solve)

Timestamping often gets treated as paperwork. In signing systems, it’s actually a practical tool for long-term verification and incident clarity.

What timestamping is (in practical terms)

A trusted timestamping service issues a signed statement that a particular artifact hash existed at (or before) a certain time.

The most commonly referenced protocol here is the Time-Stamp Protocol (TSP) from RFC 3161.
Source: https://www.rfc-editor.org/rfc/rfc3161

Why timestamping matters for code signing

Timestamping helps in a few concrete scenarios:

  1. Certificate expiry:
    You often want signatures to remain verifiable after the signing certificate expires, as long as the signature was created while the certificate was valid. Timestamping provides evidence of signing time.
  2. Key compromise / revocation timing:
    If a signing key is compromised at time T, you need to distinguish:
    • artifacts signed before T (likely legitimate), vs
    • artifacts signed after T (likely malicious).
      A trusted timestamp can help establish when an artifact was signed relative to an incident.
  3. Long-lived artifacts:
    Firmware images and offline installers may need to be validated long after issuance. Timestamping is one piece of maintaining verifiability over time, alongside retention of certificates and revocation evidence.

What timestamping does not do

Timestamping is not a magic shield:

  • It does not make an insecure signature algorithm “secure.”
  • If an algorithm becomes practically breakable, you still have a problem. Timestamping can help with policy and evidence questions, but it doesn’t undo cryptographic failure.

The reason to include this nuance is simple: timestamping is valuable, but you shouldn’t treat it as a substitute for migration planning.

Operational guidance: building a signing system that survives PQC transition

Keep signing keys boring and hard to misuse

For high-value signing keys (code/firmware), best practice is to ensure:

  • keys are non-exportable (often HSM-backed)
  • signing operations are controlled by strongly authenticated identities
  • signing requests are logged with minimal but sufficient metadata
  • access is separated by role (request vs approve vs operate)

Separate “signing policy” from “build mechanics”

A resilient setup lets you change:

  • algorithms,
  • key custody,
  • certificate profiles,
  • timestamping configuration,

…without rewriting build scripts across every repository. PQC transitions are much easier when signing is a managed service with policy at the center.

Make verification and rollback testable

Every signing change should be tested against:

  • representative devices and OS versions,
  • offline verifiers,
  • customer environments (if applicable),
  • “failure mode” cases (expired cert, revoked cert, missing intermediate).

The most valuable test is: “Can a production verifier validate artifacts after we rotate keys/certs or change signing settings?”

Vendor shortlist (code/firmware signing + timestamping ecosystem)

This shortlist is intentionally tight and category-based. The goal is to list widely used anchors that map to real purchasing decisions.

Disclosure: Some outbound links may be affiliate or referral links. This does not change which tools are included.

Code signing platforms (workflow, policy, audit)

Best for: centralized signing workflows, approvals, audit trails, and integrating HSM-backed signing into CI/CD.

Timestamping services

Best for: RFC 3161 timestamp tokens used to support long-term verification and incident clarity.

HSMs (hardware-backed signing keys)

Best for: protecting high-value signing keys and enforcing non-exportability and separation of duties.

Common mistakes (what derails PQC signing projects)

  • Treating signing as “just another PKI issue” and missing verifier constraints.
  • Migrating signing algorithms without a plan for trust store and verifier updates.
  • Forgetting that signature size changes can break embedded verifiers and artifact formats.
  • No incident playbook for signing key compromise and emergency re-sign.
  • Over-logging raw signature blobs and artifacts (creates storage and exposure risk).
  • Assuming timestamping “solves” cryptographic deprecation rather than supporting verification policy.

FAQ

Which PQC signature standards are relevant to code/firmware signing?

The relevant NIST standards are FIPS 204 (ML‑DSA) and FIPS 205 (SLH‑DSA), plus SP 800‑208 (LMS/XMSS) for hash-based signatures commonly discussed in firmware/software signing contexts.

Does CNSA 2.0 allow SLH‑DSA for NSS use?

No. The NSA CNSA 2.0 FAQ states SLH‑DSA is not approved for any use in NSS, even though NIST standardized it in FIPS 205.

Why do firmware signing migrations take longer than server-side crypto migrations?

Because verifiers are harder to update. Firmware verification often lives in constrained boot code or device ecosystems with long replacement cycles and limited crypto library support.

What does timestamping actually buy you?

Timestamping provides a trusted statement about when an artifact hash existed. This helps signatures remain acceptable after certificate expiry, helps incident response when keys are compromised, and supports long-lived verification workflows.

Should we adopt PQC signatures everywhere immediately?

Usually no. Most organizations start where they control verifiers (internal distribution, controlled device fleets) and expand outward as ecosystem support matures. The right plan is driven by verifier reality, not enthusiasm.

Further reading (primary sources)

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