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Signature Verification

Upbound Official Providers contain verifiable signatures, attestations, and an SBOM (software bill of materials). This approach lets you confirm the origin of each package version and verify that its contents remain unchanged and intact from a security standpoint. This article explains how to verify the signature on these packages.

Prerequisites​

Upbound recommends using cosign to verify the signature and attestations of an Official Provider.

If you're running UXP, enable these features first:

helm upgrade crossplane --install \
upbound-stable/universal-crossplane \
--debug \
--namespace crossplane-system \
--create-namespace --set args='{--enable-signature-verification,--enable-dependency-version-upgrades}'

Attestations​

To provide attestations per version of a package, specify the correct tag or digest and registry when pulling attestations from an image with cosign. Use the cosign verify-attestation command to verify the SBOM attestation of the image for the package. signatures

cosign verify-attestation xpkg.upbound.io/upbound/<provider>@sha256:<digest> \
--certificate-identity https://github.com/upbound/upbound-official-build/.github/workflows/supplychain.yml@refs/heads/main \
--certificate-oidc-issuer https://token.actions.githubusercontent.com  \
--type spdxjson > attestation.json

Official Provider SBOMs are produced in the SPDX format, specified by --type spdxjson. Upon successful execution, the output verifies the SBOM attestation signature in the Rekor transparency log.

Verify signatures​

Upbound performs keyless signing for Official providers using Sigstore, and you can similarly verify package signatures using cosign.

cosign verify xpkg.upbound.io/upbound/<provider>@sha256:<digest> \
--certificate-identity https://github.com/upbound/upbound-official-build/.github/workflows/supplychain.yml@refs/heads/main \
--certificate-oidc-issuer https://token.actions.githubusercontent.com  \

Using ImageConfig in Crossplane for Verification​

Starting in Crossplane 1.18, you can enable and configure an ImageConfig resource to automatically verify package signatures in your Crossplane cluster.

For example, the following configuration verifies images matching spec.matchImages.prefix using GitHub as the certificate issuer for the email identity.

apiVersion: pkg.crossplane.io/v1beta1
kind: ImageConfig
metadata:
  name: verify-upbound-official
spec:
  matchImages:
    - prefix: "xpkg.upbound.io/upbound/<the-signed-image>:"
  verification:
    provider: Cosign
    cosign:
      authorities:
        - name: verify upbound official build
          keyless:
            identities:
              - issuer: https://token.actions.githubusercontent.com
                subject: https://github.com/upbound/upbound-official-build/.github/workflows/supplychain.yml@refs/heads/main

If the signature verification feature is enabled, Crossplane ensures the status condition of type Verified is set to true on the ProviderRevision resource, indicating it was either skipped or succeeded.

For example:

  - lastTransitionTime: "2024-10-23T16:43:05Z"
    message: Signature verification succeeded with ImageConfig named "verify-upbound-official"
    reason: VerificationSucceeded
    status: "True"
    type: SignatureVerificationComplete

For further details on verifying signatures with Crossplane, refer to the Crossplane documentation.