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docs(security): document the cosign signature-format requirement - #1071
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castrojo merged 1 commit intoAug 9, 2026
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containers/image (podman, skopeo, bootc switch) discovers signatures only via the legacy sha256-<digest>.sig tag, never the OCI 1.1 referrers API — which GHCR does not implement in any case. cosign 3.x defaults --new-bundle-format=true, which writes signatures as OCI referrers instead, producing images that cosign verify accepts and podman rejects. Record why a green cosign verify is not sufficient evidence, and how to check the tag that actually matters. Refs projectbluefin/common#977, projectbluefin/actions#420
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This was referenced Aug 9, 2026
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Documents the signature-format requirement that
containers/imageimposes on us, and why a greencosign verifyis not evidence an image is verifiable by podman orbootc switch.Context: every projectbluefin image built since ~2026-06-08 is signed in a format podman cannot see, because cosign 3.x flipped
--new-bundle-formatto defaulttrueand writes signatures as OCI 1.1 referrers instead of the legacysha256-<digest>.sigtag. CI reported signing as successful throughout, becausecosign verifyaccepts both formats.This PR is docs-only — no workflow or build change. It also serves as the consumer-validation PR for projectbluefin/actions#420 per that repo's
docs/skills/consumer-validation.md.