Verify Signed Kubernetes Artifacts

FEATURE STATE: Kubernetes v1.26 [beta]

Before you begin

These instructions are for Kubernetes 1.27. If you want to check the integrity of components for a different version of Kubernetes, check the documentation for that Kubernetes release.

You will need to have the following tools installed:

  • cosign (install guide)
  • curl (often provided by your operating system)

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/v1.27.0/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:

  1. cosign verify-blob "$BINARY" --signature "$BINARY".sig --certificate "$BINARY".cert

cosign v1.9.0 is required to be able to use the --certificate flag. Please use --cert for older versions of cosign.

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

Verifying image signatures

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

Let’s pick one image from this list and verify its signature using the cosign verify command:

  1. COSIGN_EXPERIMENTAL=1 cosign verify registry.k8s.io/kube-apiserver-amd64:v1.27.0

Note: COSIGN_EXPERIMENTAL=1 is used to allow verification of images signed in KEYLESS mode. To learn more about keyless signing, please refer to Keyless Signatures .

Verifying images for all control plane components

To verify all signed control plane images, please run this command:

  1. curl -Ls https://sbom.k8s.io/$(curl -Ls https://dl.k8s.io/release/latest.txt)/release | grep 'PackageName: registry.k8s.io/' | awk '{print $2}' > images.txt
  2. input=images.txt
  3. while IFS= read -r image
  4. do
  5.   COSIGN_EXPERIMENTAL=1 cosign verify "$image"
  6. done < "$input"

Once you have verified an image, specify that image by its digest in your Pod manifests as per this example: registry-url/image-name@sha256:45b23dee08af5e43a7fea6c4cf9c25ccf269ee113168c19722f87876677c5cb2 .

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

Verifying Image Signatures with Admission Controller

For non-control plane images ( e.g. conformance image) , signatures can also be verified at deploy time using sigstore policy-controller admission controller. To get started with policy-controller here are a few helpful resources: