Verify Signed Kubernetes Artifacts

FEATURE STATE: Kubernetes v1.26 [beta]

Before you begin

You will need to have the following tools installed:

Verifying binary signatures

The Kubernetes release process signs all binary artifacts (tarballs, SPDX files, standalone binaries) by using cosign’s keyless signing. To verify a particular binary, retrieve it together with its signature and certificate:

  1. URL=https://dl.k8s.io/release/v1.28.0/bin/linux/amd64
  2. BINARY=kubectl
  4. FILES=(
  5.     "$BINARY"
  6.     "$BINARY.sig"
  7.     "$BINARY.cert"
  8. )
  10. for FILE in "${FILES[@]}"; do
  11.     curl -sSfL --retry 3 --retry-delay 3 "$URL/$FILE" -o "$FILE"
  12. done

Then verify the blob by using cosign verify-blob:

  1. cosign verify-blob "$BINARY" \
  2.   --signature "$BINARY".sig \
  3.   --certificate "$BINARY".cert \
  4.   --certificate-identity krel-staging@k8s-releng-prod.iam.gserviceaccount.com \
  5.   --certificate-oidc-issuer https://accounts.google.com

Note:

Cosign 2.0 requires the --certificate-identity and --certificate-oidc-issuer options.

To learn more about keyless signing, please refer to Keyless Signatures.

Previous versions of Cosign required that you set COSIGN_EXPERIMENTAL=1.

For additional information, plase refer to the sigstore Blog

Verifying image signatures

For a complete list of images that are signed please refer to Releases.

Pick one image from this list and verify its signature using the cosign verify command:

  1. cosign verify registry.k8s.io/kube-apiserver-amd64:v1.28.0 \
  2.   --certificate-identity krel-trust@k8s-releng-prod.iam.gserviceaccount.com \
  3.   --certificate-oidc-issuer https://accounts.google.com \
  4.   | jq .

Verifying images for all control plane components

To verify all signed control plane images for the latest stable version (v1.28.0), please run the following commands:

  1. curl -Ls "https://sbom.k8s.io/$(curl -Ls https://dl.k8s.io/release/stable.txt)/release" \
  2.   | grep "SPDXID: SPDXRef-Package-registry.k8s.io" \
  3.   | grep -v sha256 | cut -d- -f3- | sed 's/-/\//' | sed 's/-v1/:v1/' \
  4.   | sort > images.txt
  5. input=images.txt
  6. while IFS= read -r image
  7. do
  8.   cosign verify "$image" \
  9.     --certificate-identity krel-trust@k8s-releng-prod.iam.gserviceaccount.com \
  10.     --certificate-oidc-issuer https://accounts.google.com \
  11.     | jq .
  12. done < "$input"

Once you have verified an image, you can specify the image by its digest in your Pod manifests as per this example:

  1. registry-url/image-name@sha256:45b23dee08af5e43a7fea6c4cf9c25ccf269ee113168c19722f87876677c5cb2

For more information, please refer to the Image Pull Policy section.

Verifying Image Signatures with Admission Controller

For non-control plane images (for example conformance image), signatures can also be verified at deploy time using sigstore policy-controller admission controller.

Here are some helpful resources to get started with policy-controller: