Chains Configuration

Chains works by observing TaskRun executions, capturing relevant information, and storing it in a cryptographically-signed format.

TaskRuns can indicate inputs and outputs which are then captured and surfaced in the Chains payload formats, where relevant. Chains uses the standard mechanisms (Results and PipelineResources) where possible, and provides a few other mechanisms to hint at the correct inputs and outputs. These are outlined below:

Chains Type Hinting

When outputting an OCI image without using a PipelineResource, Chains will look for the following Results:

  • *IMAGE_URL - The URL to the built OCI image
  • *IMAGE_DIGEST - The Digest of the built OCI image

where * indicates any expression. For example, if both MYIMAGE_IMAGE_URL AND MYIMAGE_IMAGE_DIGEST are correctly formatted to point to an OCI image, then chains will pick up on it and try to sign the image.

Multiple images can be specified by using different prefixes in place of *.

Multiple images can also be specified by using the IMAGES Result. The value of the IMAGES result is a list of images, each qualified by digest. The list of images can be separated by commas or by newlines.

- name: IMAGES
  value: img1@sha256:digest1, img2@sha256:digest2

Chains will parse through the list and sign each image.

For in-toto attestations, see intoto.md for description of in-toto specific type hinting.

Note that these are provided automatically when using PipelineResources.

Chains Configuration

Chains uses a ConfigMap called chains-config in the tekton-chains namespace for configuration. Supported keys include:

TaskRun Configuration

Key Description Supported Values Default
artifacts.taskrun.format The format to store TaskRun payloads in. tekton, in-toto tekton
artifacts.taskrun.storage The storage backend to store TaskRun signatures in. Multiple backends can be specified with comma-separated list (“tekton,oci”). To disable the TaskRun artifact input an empty string (""). tekton, oci, gcs, docdb, grafeas tekton
artifacts.taskrun.signer The signature backend to sign Taskrun payloads with. x509, kms x509

NOTE: For grafeas storage backend, currently we only support Container Analysis. We will make grafeas server address configurabe within a short time.

OCI Configuration

Key Description Supported Values Default
artifacts.oci.format The format to store OCI payloads in. simplesigning simplesigning
artifacts.oci.storage The storage backend to store OCI signatures in. Multiple backends can be specified with comma-separated list (“oci,tekton”). To disable the OCI artifact input an empty string (""). tekton, oci, gcs, docdb, grafeas oci
artifacts.oci.signer The signature backend to sign OCI payloads with. x509, kms x509

KMS Configuration

Key Description Supported Values Default
signers.kms.kmsref The URI reference to a KMS service to use in KMS signers. One of the three formats:
gcpkms://projects/[PROJECT]/locations/[LOCATION]>/keyRings/[KEYRING]/cryptoKeys/[KEY]
gcpkms://projects/[PROJECT]/locations/[LOCATION]>/keyRings/[KEYRING]/cryptoKeys/[KEY]/cryptoKeyVersions/[KEY_VERSION]
gcpkms://projects/[PROJECT]/locations/[LOCATION]>/keyRings/[KEYRING]/cryptoKeys/[KEY]/versions/[KEY_VERSION]

Storage Configuration

Key Description Supported Values Default
storage.gcs.bucket The GCS bucket for storage
storage.oci.repository The OCI repo to store OCI signatures and attestation in If left undefined and one of artifacts.{oci,taskrun}.storage includes oci storage, attestations will be stored alongside the stored OCI artifact itself. (example on GCP) Defining this value results in the OCI bundle stored in the designated location instead of alongside the image. See cosign documentation for additional information.
storage.docdb.url The go-cloud URI reference to a docstore collection firestore://projects/[PROJECT]/databases/(default)/documents/[COLLECTION]?name_field=name
storage.grafeas.projectid The project of where grafeas server is located for storing occurrences
storage.grafeas.noteid (optional) This field will be used as the prefix part of the note name that will be created. The value of this field must be a string without spaces. (See more details below.)
storage.grafeas.notehint (optional) This field is used to set the human_readable_name field in the Grafeas ATTESTATION note. If it is not provided, the default This attestation note was generated by Tekton Chains will be used.

docstore

You can read about the go-cloud docstore URI format here. Tekton Chains supports the following docstore services:

  • firestore
  • dynamodb
  • mongo

MongoDB

With MongoDB you will need to add a MONGO_SERVER_URL env var with the MongoDB connection URI to the tekton-chains-controller, the go-cloud URI is just to point at the db and collection

Grafeas

You can read more about Grafeas notes and occurrences here. To create occurrences, we have to create notes first that are used to link occurrences. Two types of occurrences will be created: ATTESTATION Occurrence and BUILD Occrrence. The configurable noteid is used as the prefix of the note name. Under the hood, the suffix -simplesigning will be appended for the ATTESTATION note, and the suffix -intoto will be appended for the BUILD note. If the noteid field is not configured, tekton-<NAMESPACE> will be used as the prefix.

In-toto Configuration

Key Description Supported Values Default
builder.id The builder ID to set for in-toto attestations https://tekton.dev/chains/v2

Experimental Features Configuration

Transparency Log

Key Description Supported Values Default
transparency.enabled EXPERIMENTAL. Whether to enable automatic binary transparency uploads. true, false, manual false
transparency.url EXPERIMENTAL. The URL to upload binary transparency attestations to, if enabled. https://rekor.sigstore.dev

Note: If transparency.enabled is set to manual, then only TaskRuns with the following annotation will be uploaded to the transparency log:

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

Keyless Signing with Fulcio

Key Description Supported Values Default
signers.x509.fulcio.enabled EXPERIMENTAL. Whether to enable automatic certificates from fulcio. true, false false
signers.x509.fulcio.address EXPERIMENTAL. Fulcio address to request certificate from, if enabled https://v1.fulcio.sigstore.dev
signers.x509.fulcio.issuer EXPERIMENTAL. Expected OIDC issuer. https://oauth2.sigstore.dev/auth
signers.x509.fulcio.provider EXPERIMENTAL. Provider to request ID Token from google, spiffe, github, filesystem Unset, each provider will be attempted.

KMS OIDC and Spire Configuration

Key Description Supported Values Default
signers.kms.auth.address URI of KMS server (e.g. the value of VAULT_ADDR)
signers.kms.auth.token Auth token KMS server (e.g. the value of VAULT_TOKEN)
signers.kms.auth.oidc.path Path used for OIDC authentication (e.g. jwt for Vault)
signers.kms.auth.oidc.role Role used for OIDC authentication
signers.kms.auth.spire.sock URI of the Spire socket used for KMS token (e.g. unix:///tmp/spire-agent/public/api.sock)
signers.kms.auth.spire.audience Audience for requesting a SVID from Spire