Here’s a practical, low‑friction way to modernize how you sign and verify build “verdicts” in CI/CD using Sigstore—no long‑lived keys, offline‑friendly, and easy to audit.

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### 1) Use **keyless** signing in CI

* In your pipeline, obtain an OIDC token (from your CI runner) and let **Fulcio** issue a short‑lived X.509 code‑signing cert (~10 minutes). You sign with the ephemeral key; cert + signature are logged to Rekor. ([Sigstore Blog][1])

**Why:** no key escrow in CI, nothing persistent to steal, and every signature is time‑bound + transparency‑logged.

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### 2) Keep one **hardware‑backed org key** only for special cases

* Reserve a physical HSM/YubiKey (or KMS) key for:
  a) re‑signing monthly bundles (see §4), and
  b) offline/air‑gapped verification workflows where a trust anchor is needed.
  Cosign supports disconnected/offline verification patterns and mirroring the proof data. ([Sigstore][2])

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### 3) Make “verdicts” first‑class OCI attestations

* Emit DSSE/attestations (SBOM deltas, reachability graphs, policy results) as OCI‑attached artifacts and sign them with keyless in CI. (Cosign is designed to sign/verify arbitrary OCI artifacts alongside images.) ([Artifact Hub][3])

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### 4) Publish a **rotation & refresh policy**

* Every month, collect older attestations and **re‑sign into a long‑lived “bundle”** (plus timestamps) using the org key. This keeps proofs verifiable over years—even if the 10‑minute certs expire—because the bundle contains the cert chain, Rekor inclusion proof, and timestamps suitable for **offline** verification. ([Trustification][4])

**Suggested SLOs**

* CI keyless cert TTL: 10 minutes (Fulcio default). ([Sigstore][5])
* Bundle cadence: monthly (or per release); retain N=24 months.

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### 5) Offline / air‑gapped verification

* Mirror the image + attestation + Rekor proof (or bundle) into the disconnected registry. Verify with `cosign verify` using the mirrored materials—no internet needed. (Multiple guides show fully disconnected OpenShift/air‑gapped flows.) ([Red Hat Developer][6])

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### 6) Address common concerns (“myths”)

* “Short‑lived certs will break verification later.” → They don’t: you verify against the Rekor proof/bundle, not live cert validity. ([Trustification][4])
* “Keyless means less security.” → The opposite: no static secrets in CI; certs expire in ~10 minutes; identity bound via OIDC and logged. ([Chainguard][7])

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### Minimal rollout checklist

* [ ] Enable OIDC on your CI runners; test `cosign sign --identity-token ...`
* [ ] Enforce identity/issuer in policy: `--certificate-identity` + `--certificate-oidc-issuer` at verify time. ([Sigstore][2])
* [ ] Set up a monthly job to build **Sigstore bundles** from past attestations and re‑sign with the org key. ([Trustification][4])
* [ ] For offline sites: mirror images + attestations + bundles; verify with `cosign verify` entirely offline. ([Red Hat Developer][6])

Want me to draft the exact cosign commands and a GitLab/GitHub Actions snippet for your Stella Ops pipelines (keyless sign, verify gates, monthly bundling, and an offline verification playbook)?

[1]: https://blog.sigstore.dev/trusted-time/?utm_source=chatgpt.com "Trusted Time in Sigstore"
[2]: https://docs.sigstore.dev/cosign/verifying/verify/?utm_source=chatgpt.com "Verifying Signatures - Cosign"
[3]: https://artifacthub.io/packages/container/cosign/cosign/latest?utm_source=chatgpt.com "cosign latest · sigstore/cosign"
[4]: https://trustification.io/blog/?utm_source=chatgpt.com "Blog"
[5]: https://docs.sigstore.dev/certificate_authority/overview/?utm_source=chatgpt.com "Fulcio"
[6]: https://developers.redhat.com/articles/2025/08/27/how-verify-container-signatures-disconnected-openshift?utm_source=chatgpt.com "How to verify container signatures in disconnected OpenShift"
[7]: https://www.chainguard.dev/unchained/life-of-a-sigstore-signature?utm_source=chatgpt.com "Life of a Sigstore signature"