We're signing our built images, but that doesn't tell us whether the base image or dependencies were trustworthy before the build. How are people verifying those inputs, and where do you enforce the checks?
What does signing a container image actually prove?
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g903-tinfoil
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A valid signature binds the signed image digest to a signing identity or key. If you trust that identity and know how its key is used, it can help establish who signed the image and detect changes to the signed content. It doesn't prove the build was clean or that every input was safe.
For base images, pin the digest and verify the publisher's signature and expected identity before building. Check every base used by a multi-stage build, not just the final stage. Then sign your output and attach provenance so consumers can check what built it and which inputs were recorded. The provenance is only as trustworthy as the system producing it.
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Dependency signing is patchy, so lockfiles and checksums are useful even though they answer a narrower question. They can catch unexpected changes to the bytes you intended to install, but they don't establish that the original package was legitimate or uncompromised.
Be careful about where dependencies resolve from, especially when private and public package names can overlap. A trusted registry or proxy and explicit source configuration can reduce confusion. Review dependency updates and scan the resulting image too, but a clean scan isn't proof that nothing malicious is present.
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I'd put checks in both places. Fail the build when a base image fails your signature policy, then have an admission policy verify the final image before it runs. Tools like Kyverno or OPA can enforce that policy, but make sure it checks the expected signer rather than accepting just any signature.
Start admission checks in audit mode. Mesh sidecars, init containers and other third-party images can get caught alongside your own workloads. Inventory those first and make any exceptions deliberate before switching to enforcement.
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A maintained, signed base from a provider can save you a lot of work compared with building and signing every base yourself. Check what the provider actually supplies, such as signatures, provenance or an SBOM, and whether that meets your policy.
You can also build your own minimal bases if you need tighter control. Either way, keep scanning and updating them. A signature doesn't mean an image is free of vulnerabilities.
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Jexlor-4m:
Digest pinning also makes the verified base explicit. You'll still need a process to update the pin as fixes come out.