Chapter 4. Creating and verifying task run signatures without any additional authentication

Procedure

1. Generate an encrypted x509 or cosign key pair. For more information about creating a key pair and saving it as a secret, see "Secrets for signing data in Tekton Chains".

2. In the Tekton Chains configuration, disable the Open Container Initiative (OCI) storage, and set the task run storage and format to tekton. In the TektonConfig custom resource set the following values:

   apiVersion: operator.tekton.dev/v1alpha1
   kind: TektonConfig
   metadata:
     name: config
   spec:
   # ...
       chain:
         artifacts.oci.storage: ""
         artifacts.taskrun.format: tekton
         artifacts.taskrun.storage: tekton
   # ...

   For more information about configuring Tekton Chains using the TektonConfig custom resource, see "Configuring Tekton Chains".

3. To restart the Tekton Chains controller to apply the modified configuration, enter the following command:

   $ oc delete po -n openshift-pipelines -l app=tekton-chains-controller

4. Create a task run by entering the following command:

   $ oc create -f https://raw.githubusercontent.com/tektoncd/chains/main/examples/taskruns/task-output-image.yaml

   -f

   Replace the example URI with the URI or file path pointing to your task run.

   Example output

   taskrun.tekton.dev/build-push-run-output-image-qbjvh created

5. Check the status of the steps by entering the following command. Wait until the process finishes.

   $ tkn tr describe --last

   Example output

   [...truncated output...]
   NAME                            STATUS
   ∙ create-dir-builtimage-9467f   Completed
   ∙ git-source-sourcerepo-p2sk8   Completed
   ∙ build-and-push                Completed
   ∙ echo                          Completed
   ∙ image-digest-exporter-xlkn7   Completed

6. To retrieve the signature from the object stored as base64 encoded annotations, enter the following commands:

   $ tkn tr describe --last -o jsonpath="{.metadata.annotations.chains\.tekton\.dev/signature-taskrun-$TASKRUN_UID}" | base64 -d > sig

   $ export TASKRUN_UID=$(tkn tr describe --last -o  jsonpath='{.metadata.uid}')

7. To verify the signature using the public key that you created, enter the following command:

   $ cosign verify-blob-attestation --insecure-ignore-tlog --key path/to/cosign.pub --signature sig --type slsaprovenance --check-claims=false /dev/null

   --insecure-ignore-tlog

   Replace path/to/cosign.pub with the path name of the public key file.

   Example output

   Verified OK