Using Tekton Chains for OpenShift Pipelines supply chain security | Securing OpenShift Pipelines

Key features
Configuring Tekton Chains
- Supported parameters for Tekton Chains configuration
Secrets for signing data in Tekton Chains
Authenticating to an OCI registry
Creating and verifying task run signatures without any additional authentication
- Additional resources
Using Tekton Chains to sign and verify image and provenance
Additional resources

Tekton Chains is a Kubernetes Custom Resource Definition (CRD) controller. You can use it to manage the supply chain security of the tasks and pipelines created using Red Hat OpenShift Pipelines.

By default, Tekton Chains observes all task run executions in your OpenShift Container Platform cluster. When the task runs complete, Tekton Chains takes a snapshot of the task runs. It then converts the snapshot to one or more standard payload formats, and finally signs and stores all artifacts.

To capture information about task runs, Tekton Chains uses Result objects. When the objects are unavailable, Tekton Chains the URLs and qualified digests of the OCI images.

Key features

You can sign task runs, task run results, and OCI registry images with cryptographic keys that are generated by tools such as cosign and skopeo.
You can use attestation formats such as in-toto.
You can securely store signatures and signed artifacts using OCI repository as a storage backend.

Configuring Tekton Chains

The Red Hat OpenShift Pipelines Operator installs Tekton Chains by default. You can configure Tekton Chains by modifying the TektonConfig custom resource; the Operator automatically applies the changes that you make in this custom resource.

To edit the custom resource, use the following command:

$ oc edit TektonConfig config

The custom resource includes a chain: array. You can add any supported configuration parameters to this array, as shown in the following example:

apiVersion: operator.tekton.dev/v1alpha1
kind: TektonConfig
metadata:
  name: config
spec:
  addon: {}
  chain:
    artifacts.taskrun.format: tekton
  config: {}

Supported parameters for Tekton Chains configuration

Cluster administrators can use various supported parameter keys and values to configure specifications about task runs, OCI images, and storage.

Supported parameters for task run artifacts

Table 1. Chains configuration: Supported parameters for task run artifacts
Key	Description	Supported values	Default value
`artifacts.taskrun.format`	The format for storing task run payloads.	`in-toto`, `slsa/v1`	`in-toto`
`artifacts.taskrun.storage`	The storage backend for task run signatures. You can specify multiple backends as a comma-separated list, such as `“tekton,oci”`. To disable storing task run artifacts, provide an empty string `“”`.	`tekton`, `oci`, `gcs`, `docdb`, `grafeas`	`tekton`
`artifacts.taskrun.signer`	The signature backend for signing task run payloads.	`x509`,`kms`	`x509`

slsa/v1 is an alias of in-toto for backwards compatibility.

Supported parameters for pipeline run artifacts

Table 2. Chains configuration: Supported parameters for pipeline run artifacts
Parameter	Description	Supported values	Default value
`artifacts.pipelinerun.format`	The format for storing pipeline run payloads.	`in-toto`, `slsa/v1`	`in-toto`
`artifacts.pipelinerun.storage`	The storage backend for storing pipeline run signatures. You can specify multiple backends as a comma-separated list, such as `“tekton,oci”`. To disable storing pipeline run artifacts, provide an empty string `“”`.	`tekton`, `oci`, `gcs`, `docdb`, `grafeas`	`tekton`
`artifacts.pipelinerun.signer`	The signature backend for signing pipeline run payloads.	`x509`, `kms`	`x509`

slsa/v1 is an alias of in-toto for backwards compatibility.
For the grafeas storage backend, only Container Analysis is supported. You can not configure the grafeas server address in the current version of Tekton Chains.

Supported parameters for OCI artifacts

Table 3. Chains configuration: Supported parameters for OCI artifacts
Parameter	Description	Supported values	Default value
`artifacts.oci.format`	The format for storing OCI payloads.	`simplesigning`	`simplesigning`
`artifacts.oci.storage`	The storage backend for storing OCI signatures. You can specify multiple backends as a comma-separated list, such as `“oci,tekton”`. To disable storing OCI artifacts, provide an empty string `“”`.	`tekton`, `oci`, `gcs`, `docdb`, `grafeas`	`oci`
`artifacts.oci.signer`	The signature backend for signing OCI payloads.	`x509`, `kms`	`x509`

Supported parameters for KMS signers

Table 4. Chains configuration: Supported parameters for KMS signers
Parameter	Description	Supported values	Default value
`signers.kms.kmsref`	The URI reference to a KMS service to use in `kms` signers.	Supported schemes: `gcpkms://`, `awskms://`, `azurekms://`, `hashivault://`. See KMS Support in the Sigstore documentation for more details.

Supported parameters for storage

Table 5. Chains configuration: Supported parameters for storage
Parameter	Description	Supported values	Default value
`storage.gcs.bucket`	The GCS bucket for storage
`storage.oci.repository`	The OCI repository for storing OCI signatures and attestation.	If you configure one of the artifact storage backends to `oci` and do not define this key, Tekton Chains stores the attestation alongside the stored OCI artifact itself. If you define this key, the attestation is not stored alongside the OCI artifact and is instead stored in the designated location. See the cosign documentation for additional information.
`builder.id`	The builder ID to set for in-toto attestations		`https://tekton.dev/chains/v2`

If you enable the docdb storage method is for any artifacts, configure docstore storage options. For more information about the go-cloud docstore URI format, see the docstore package documentation. Red Hat OpenShift Pipelines supports the following docstore services:

firestore
dynamodb

Table 6. Chains configuration: Supported parameters for `docstore` storage
Parameter	Description	Supported values	Default value
`storage.docdb.url`	The go-cloud URI reference to a `docstore` collection. Used if the `docdb` storage method is enabled for any artifacts.	`firestore://projects/[PROJECT]/databases/(default)/documents/[COLLECTION]?name_field=name`

If you enable the grafeas storage method for any artifacts, configure Grafeas storage options. For more information about Grafeas notes and occurrences, see Grafeas concepts.

To create occurrences, Red Hat OpenShift Pipelines must first create notes that are used to link occurrences. Red Hat OpenShift Pipelines creates two types of occurrences: ATTESTATION Occurrence and BUILD Occurrence.

Red Hat OpenShift Pipelines uses the configurable noteid as the prefix of the note name. It appends the suffix -simplesigning for the ATTESTATION note and the suffix -intoto for the BUILD note. If the noteid field is not configured, Red Hat OpenShift Pipelines uses tekton-<NAMESPACE> as the prefix.

Table 7. Chains configuration: Supported parameters for Grafeas storage
Parameter	Description	Supported values	Default value
`storage.grafeas.projectid`	The OpenShift Container Platform project in which the Grafeas server for storing occurrences is located.
`storage.grafeas.noteid`	Optional: the prefix to use for the name of all created notes.	A string without spaces.
`storage.grafeas.notehint`	Optional: the `human_readable_name` field for the Grafeas `ATTESTATION` note.		`This attestation note was generated by Tekton Chains`

Optionally, you can enable additional uploads of binary transparency attestations.

Table 8. Chains configuration: Supported parameters for transparency attestation storage
Parameter	Description	Supported values	Default value
`transparency.enabled`	Enable or disable automatic binary transparency uploads.	`true`, `false`, `manual`	`false`
`transparency.url`	The URL for uploading binary transparency attestations, if enabled.		`https://rekor.sigstore.dev`

If you set transparency.enabled to manual, only task runs and pipeline runs with the following annotation are uploaded to the transparency log:

chains.tekton.dev/transparency-upload: "true"

If you configure the x509 signature backend, you can optionally enable keyless signing with Fulcio.

Table 9. Chains configuration: Supported parameters for `x509` keyless signing with Fulcio
Parameter	Description	Supported values	Default value
`signers.x509.fulcio.enabled`	Enable or disable requesting automatic certificates from Fulcio.	`true`, `false`	`false`
`signers.x509.fulcio.address`	The Fulcio address for requesting certificates, if enabled.		`https://v1.fulcio.sigstore.dev`
`signers.x509.fulcio.issuer`	The expected OIDC issuer.		`https://oauth2.sigstore.dev/auth`
`signers.x509.fulcio.provider`	The provider from which to request the ID Token.	`google`, `spiffe`, `github`, `filesystem`	Red Hat OpenShift Pipelines attempts to use every provider
`signers.x509.identity.token.file`	Path to the file containing the ID Token.
`signers.x509.tuf.mirror.url`	The URL for the TUF server. `$TUF_URL/root.json` must be present.		`https://sigstore-tuf-root.storage.googleapis.com`

If you configure the kms signature backend, set the KMS configuration, including OIDC and Spire, as necessary.

Table 10. Chains configuration: Supported parameters for KMS signing
Parameter	Description	Supported values	Default value
`signers.kms.auth.address`	URI of the KMS server (the value of `VAULT_ADDR`).
`signers.kms.auth.token`	Authentication token for the KMS server (the value of `VAULT_TOKEN`).
`signers.kms.auth.oidc.path`	The path for OIDC authentication (for example, `jwt` for Vault).
`signers.kms.auth.oidc.role`	The role for OIDC authentication.
`signers.kms.auth.spire.sock`	The URI of the Spire socket for the KMS token (for example, `unix:///tmp/spire-agent/public/api.sock`).
`signers.kms.auth.spire.audience`	The audience for requesting a SVID from Spire.

Secrets for signing data in Tekton Chains

Cluster administrators can generate a key pair and use Tekton Chains to sign artifacts using a Kubernetes secret. For Tekton Chains to work, a private key and a password for encrypted keys must exist as part of the signing-secrets secret in the openshift-pipelines namespace.

Currently, Tekton Chains supports the x509 and cosign signature schemes.

Use only one of the supported signature schemes.

To use the x509 signing scheme with Tekton Chains, store the x509.pem private key of the ed25519 or ecdsa type in the signing-secrets Kubernetes secret.

Signing using cosign

You can use the cosign signing scheme with Tekton Chains using the cosign tool.

Prerequisites

You installed the cosign tool.

Procedure

Generate the cosign.key and cosign.pub key pairs by running the following command:
```
$ cosign generate-key-pair k8s://openshift-pipelines/signing-secrets
```
Cosign prompts you for a password and then creates a Kubernetes secret.
Store the encrypted cosign.key private key and the cosign.password decryption password in the signing-secrets Kubernetes secret. Ensure that the private key is stored as an encrypted PEM file of the ENCRYPTED COSIGN PRIVATE KEY type.

Signing using skopeo

You can generate keys using the skopeo tool and use them in the cosign signing scheme with Tekton Chains.

Prerequisites

You installed the skopeo tool.

Procedure

Generate a public/private key pair by running the following command:
```
$ skopeo generate-sigstore-key --output-prefix <mykey> (1)
```
1 Replace <mykey> with a key name of your choice.

Skopeo prompts you for a passphrase for the private key and then creates the key files named <mykey>.private and <mykey>.pub.
Encode the <mykey>.pub file using the base64 tool by running the following command:
```
$ base64 -w 0 <mykey>.pub > b64.pub
```
Encode the <mykey>.private file using the base64 tool by running the following command:
```
$ base64 -w 0 <mykey>.private > b64.private
```
Encode the passhprase using the base64 tool by running the following command:
```
$ echo -n '<passphrase>' | base64 -w 0 > b64.passphrase (1)
```
1 Replace <passphrase> with the passphrase that you used for the key pair.
Create the signing-secrets secret in the openshift-pipelines namespace by running the following command:
```
$ oc create secret generic signing-secrets -n openshift-pipelines
```

Edit the signing-secrets secret by running the following command:

$ oc edit secret -n openshift-pipelines signing-secrets

Add the encoded keys in the data of the secret in the following way:

apiVersion: v1
data:
  cosign.key: <Encoded <mykey>.private> (1)
  cosign.password: <Encoded passphrase> (2)
  cosign.pub: <Encoded <mykey>.pub> (3)
immutable: true
kind: Secret
metadata:
  name: signing-secrets
# ...
type: Opaque

1	Replace `<Encoded <mykey>.private>` with the content of the `b64.private` file.
2	Replace `<Encoded passphrase>` with the content of the `b64.passphrase` file.
3	Replace `<Encoded <mykey>.pub>` with the content of the `b64.pub` file.

Resolving the "secret already exists" error

If the signing-secret secret is already populated, the command to create this secret might output the following error message:

Error from server (AlreadyExists): secrets "signing-secrets" already exists

You can resolve this error by deleting the secret.

Procedure

Delete the signing-secret secret by running the following command:
```
$ oc delete secret signing-secrets -n openshift-pipelines
```
Re-create the key pairs and store them in the secret using your preferred signing scheme.

Authenticating to an OCI registry

Before pushing signatures to an OCI registry, cluster administrators must configure Tekton Chains to authenticate with the registry. The Tekton Chains controller uses the same service account under which the task runs execute. To set up a service account with the necessary credentials for pushing signatures to an OCI registry, perform the following steps:

Procedure

Set the namespace and name of the Kubernetes service account.
```
$ export NAMESPACE=<namespace> (1)
$ export SERVICE_ACCOUNT_NAME=<service_account> (2)
```
1 The namespace associated with the service account.

2 The name of the service account.

Create a Kubernetes secret.

$ oc create secret registry-credentials \
  --from-file=.dockerconfigjson \ (1)
  --type=kubernetes.io/dockerconfigjson \
  -n $NAMESPACE

1	Substitute with the path to your Docker config file. Default path is `~/.docker/config.json`.

Give the service account access to the secret.
```
$ oc patch serviceaccount $SERVICE_ACCOUNT_NAME \
  -p "{\"imagePullSecrets\": [{\"name\": \"registry-credentials\"}]}" -n $NAMESPACE
```
If you patch the default pipeline service account that Red Hat OpenShift Pipelines assigns to all task runs, the Red Hat OpenShift Pipelines Operator will override the service account. As a best practice, you can perform the following steps:
1. Create a separate service account to assign to user’s task runs.
  $ oc create serviceaccount <service_account_name>
2. Associate the service account to the task runs by setting the value of the serviceaccountname field in the task run template.
  apiVersion: tekton.dev/v1 kind: TaskRun metadata: name: build-push-task-run-2 spec: taskRunTemplate: serviceAccountName: build-bot (1) taskRef: name: build-push ...
  1 Substitute with the name of the newly created service account.

Creating and verifying task run signatures without any additional authentication

To verify signatures of task runs using Tekton Chains with any additional authentication, perform the following tasks:

Create an encrypted x509 key pair and save it as a Kubernetes secret.
Configure the Tekton Chains backend storage.
Create a task run, sign it, and store the signature and the payload as annotations on the task run itself.
Retrieve the signature and payload from the signed task run.
Verify the signature of the task run.

Prerequisites

Ensure that the following components are installed on the cluster:

Red Hat OpenShift Pipelines Operator
Tekton Chains
Cosign

Procedure

Create an encrypted x509 key pair and save it as a Kubernetes secret. For more information about creating a key pair and saving it as a secret, see "Signing secrets in Tekton Chains".
In the Tekton Chains configuration, disable the 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".
To restart the Tekton Chains controller to ensure that the modified configuration is applied, enter the following command:
```
$ oc delete po -n openshift-pipelines -l app=tekton-chains-controller
```

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 (1)

1	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

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

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}')

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 (1)

1	Replace `path/to/cosign.pub` with the path name of the public key file. Example output `Verified OK`

Additional resources

Secrets for signing data in Tekton Chains
Configuring Tekton Chains

Using Tekton Chains to sign and verify image and provenance

Cluster administrators can use Tekton Chains to sign and verify images and provenances, by performing the following tasks:

Create an encrypted x509 key pair and save it as a Kubernetes secret.
Set up authentication for the OCI registry to store images, image signatures, and signed image attestations.
Configure Tekton Chains to generate and sign provenance.
Create an image with Kaniko in a task run.
Verify the signed image and the signed provenance.

Prerequisites

Ensure that the following are installed on the cluster:

Red Hat OpenShift Pipelines Operator
Tekton Chains
Cosign
Rekor
jq

Procedure

Create an encrypted x509 key pair and save it as a Kubernetes secret:
```
$ cosign generate-key-pair k8s://openshift-pipelines/signing-secrets
```
Provide a password when prompted. Cosign stores the resulting private key as part of the signing-secrets Kubernetes secret in the openshift-pipelines namespace, and writes the public key to the cosign.pub local file.
Configure authentication for the image registry.
1. To configure the Tekton Chains controller for pushing signature to an OCI registry, use the credentials associated with the service account of the task run. For detailed information, see the "Authenticating to an OCI registry" section.
2. To configure authentication for a Kaniko task that builds and pushes image to the registry, create a Kubernetes secret of the docker config.json file containing the required credentials.
  $ oc create secret generic <docker_config_secret_name> \ (1) --from-file <path_to_config.json> (2)
  1 Substitute with the name of the docker config secret.
  
  2 Substitute with the path to docker config.json file.

Configure Tekton Chains by setting the artifacts.taskrun.format, artifacts.taskrun.storage, and transparency.enabled parameters in the chains-config object:

$ oc patch configmap chains-config -n openshift-pipelines -p='{"data":{"artifacts.taskrun.format": "in-toto"}}'

$ oc patch configmap chains-config -n openshift-pipelines -p='{"data":{"artifacts.taskrun.storage": "oci"}}'

$ oc patch configmap chains-config -n openshift-pipelines -p='{"data":{"transparency.enabled": "true"}}'

Start the Kaniko task.
1. Apply the Kaniko task to the cluster.
  $ oc apply -f examples/kaniko/kaniko.yaml (1)
  1 Substitute with the URI or file path to your Kaniko task.
2. Set the appropriate environment variables.
  $ export REGISTRY=<url_of_registry> (1) $ export DOCKERCONFIG_SECRET_NAME=<name_of_the_secret_in_docker_config_json> (2)
  1 Substitute with the URL of the registry where you want to push the image.
  
  2 Substitute with the name of the secret in the docker config.json file.
3. Start the Kaniko task.
  $ tkn task start --param IMAGE=$REGISTRY/kaniko-chains --use-param-defaults --workspace name=source,emptyDir="" --workspace name=dockerconfig,secret=$DOCKERCONFIG_SECRET_NAME kaniko-chains
  Observe the logs of this task until all steps are complete. On successful authentication, the final image will be pushed to $REGISTRY/kaniko-chains.
Wait for a minute to allow Tekton Chains to generate the provenance and sign it, and then check the availability of the chains.tekton.dev/signed=true annotation on the task run.
```
$ oc get tr <task_run_name> \ (1)
-o json | jq -r .metadata.annotations

{
  "chains.tekton.dev/signed": "true",
  ...
}
```
1 Substitute with the name of the task run.

Verify the image and the attestation.

$ cosign verify --key cosign.pub $REGISTRY/kaniko-chains

$ cosign verify-attestation --key cosign.pub $REGISTRY/kaniko-chains

Find the provenance for the image in Rekor.
1. Get the digest of the $REGISTRY/kaniko-chains image. You can search for it ing the task run, or pull the image to extract the digest.
2. Search Rekor to find all entries that match the sha256 digest of the image.
  $ rekor-cli search --sha <image_digest> (1) <uuid_1> (2) <uuid_2> (3) ...
  1 Substitute with the sha256 digest of the image.
  
  2 The first matching universally unique identifier (UUID).
  
  3 The second matching UUID.
  
  The search result displays UUIDs of the matching entries. One of those UUIDs holds the attestation.
3. Check the attestation.
  $ rekor-cli get --uuid <uuid> --format json | jq -r .Attestation | base64 --decode | jq

Additional resources

Installing OpenShift Pipelines

1	The namespace associated with the service account.
2	The name of the service account.

1	Substitute with the name of the docker config secret.
2	Substitute with the path to docker `config.json` file.

1	Substitute with the URL of the registry where you want to push the image.
2	Substitute with the name of the secret in the docker `config.json` file.

1	Substitute with the `sha256` digest of the image.
2	The first matching universally unique identifier (UUID).
3	The second matching UUID.