Using artifact attestations to establish provenance for builds

Artifact attestations enable you to increase the supply chain security of your builds by publicly establishing where and how your software was built and associating it with a signed software bill of materials (SBOM).

In this article

Note

Artifact attestations are in public beta and subject to change.

About artifact attestations

Artifact attestations enable you to create unfalsifiable provenance and integrity guarantees for the software you build. In turn, people who consume your software can verify where and how your software was built.

When you generate artifact attestations with your software, you create cryptographically signed claims that establish your build's provenance and include the following information:

  • A link to the workflow associated with the artifact.
  • The repository, organization, environment, commit SHA, and triggering event for the artifact.
  • Other information from the OIDC token used to establish provenance. For more information, see "About security hardening with OpenID Connect."

You can also generate artifact attestations that include an associated software bill of materials (SBOM). Associating your builds with a list of the open source dependencies used in them provides transparency and enables consumers to comply with data protection standards.

About SLSA levels for artifact attestations

The SLSA framework is an industry standard used to evaluate supply chain security. It is organized into levels. Each level represents an increasing degree of security and trustworthiness for a software supply chain. Artifact attestations provides SLSA v1.0 Build Level 2.

You can use artifact attestations to achieve SLSA v1.0 Build Level 3; however, we strongly recommend first focusing on broad adoption of Build Level 2 across your organization. It is much better to consistently meet Level 2 across your builds than to have a small portion of builds that reach Level 3. To achieve Build Level 3, we recommend standardizing your build process with reusable workflows, auditing the reusable workflows to ensure they meet Level 3 requirements, and then updating your verification policy to require those audited reusable workflows.

For more information, see the Provenance section of the SLSA documentation.

About using Sigstore for artifact attestations

To generate artifact attestations, GitHub uses Sigstore, which is an open source project that offers a comprehensive solution for signing and verifying software artifacts via attestations.

Public repositories that generate artifact attestations use the Sigstore Public Good Instance. A copy of the generated Sigstore bundle is stored with GitHub and is also written to an immutable transparency log that is publicly readable on the internet.

Private repositories that generate artifact attestations use GitHub's Sigstore instance. GitHub's Sigstore instance uses the same codebase as the Sigstore Public Good Instance, but it does not have a transparency log and only federates with GitHub Actions.

About verifying artifact attestations

If you consume software that publishes artifact attestations, you can use the GitHub CLI to verify those attestations. Because the attestations give you information about where and how software was built, you can use that information to create and enforce security policies that elevate your supply chain security. For more information, see "Verifying artifact attestations with the GitHub CLI."

Warning

It is important to remember that artifact attestations are not a guarantee that an artifact is secure. Instead, artifact attestations link you to the source code and the build instructions that produced them. It is up to you to define your policy criteria, evaluate that policy by evaluating the content, and make an informed risk decision when you are consuming software.

Generating artifact attestations for your builds

You can use GitHub Actions to generate artifact attestations that establish build provenance for artifacts such as binaries and container images.

To generate an artifact attestation, you must:

  • Ensure you have the appropriate permissions configured in your workflow.
  • Include a step in your workflow that uses the attest-build-provenance action.

When you run your updated workflows, they will build your artifacts and generate an artifact attestation that establishes build provenance. You can view attestations in your repository's Actions tab. For more information, see the attest-build-provenance repository.

Generating build provenance for binaries

  1. In the workflow that builds the binary you would like to attest, add the following permissions.

    permissions:
  id-token: write
  contents: read
  attestations: write

  2. After the step where the binary has been built, add the following step.

    - name: Generate artifact attestation
  uses: actions/attest-build-provenance@v1
  with:
    subject-path: 'PATH/TO/ARTIFACT'

    The value of the subject-path parameter should be set to the path to the binary you want to attest.

Generating build provenance for container images

  1. In the workflow that builds the container image you would like to attest, add the following permissions.

    permissions:
  id-token: write
  contents: read
  attestations: write
  packages: write

  2. After the step where the image has been built, add the following step.

    - name: Generate artifact attestation
  uses: actions/attest-build-provenance@v1
  with:
    subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
    subject-digest: 'sha256:fedcba0...'
    push-to-registry: true

    The value of the subject-name parameter should specify the fully-qualified image name. For example, ghcr.io/user/app or acme.azurecr.io/user/app. Do not include a tag as part of the image name.

    The value of the subject-digest parameter should be set to the SHA256 digest of the subject for the attestation, in the form sha256:HEX_DIGEST. If your workflow uses docker/build-push-action, you can use the digest output from that step to supply the value. For more information on using outputs, see "Workflow syntax for GitHub Actions."

Generating an attestation for a software bill of materials (SBOM)

You can generate signed SBOM attestations for workflow artifacts.

To generate an attestation for an SBOM, you must:

  • Ensure you have the appropriate permissions configured in your workflow.
  • Create an SBOM for your artifact. For more information, see anchore-sbom-action in the GitHub Marketplace.
  • Include a step in your workflow that uses the attest-sbom action.

When you run your updated workflows, they will build your artifacts and generate an SBOM attestation. You can view attestations in your repository's Actions tab. For more information, see the attest-sbom action repository.

Generating an SBOM attestation for binaries

  1. In the workflow that builds the binary you would like to attest, add the following permissions.

    permissions:
  id-token: write
  contents: read
  attestations: write

  2. After the step where the binary has been built, add the following step.

    - name: Generate SBOM attestation
  uses: actions/attest-sbom@v1
  with:
    subject-path: 'PATH/TO/ARTIFACT'
    sbom-path: 'PATH/TO/SBOM'

    The value of the subject-path parameter should be set to the path of the binary the SBOM describes. The value of the sbom-path parameter should be set to the path of the SBOM file you generated.

Generating an SBOM attestation for container images

  1. In the workflow that builds the container image you would like to attest, add the following permissions.

    permissions:
  id-token: write
  contents: read
  attestations: write
  packages: write

  2. After the step where the image has been built, add the following step.

    - name: Generate SBOM attestation
  uses: actions/attest-sbom@v1
  with:
    subject-name: ${{ env.REGISTRY }}/PATH/TO/IMAGE
    subject-digest: 'sha256:fedcba0...'
    sbom-path: 'sbom.json'
    push-to-registry: true

    The value of the subject-name parameter should specify the fully-qualified image name. For example, ghcr.io/user/app or acme.azurecr.io/user/app. Do not include a tag as part of the image name.

    The value of the subject-digest parameter should be set to the SHA256 digest of the subject for the attestation, in the form sha256:HEX_DIGEST. If your workflow uses docker/build-push-action, you can use the digest output from that step to supply the value. For more information on using outputs, see "Workflow syntax for GitHub Actions."

    The value of the sbom-path parameter should be set to the path to the JSON-formatted SBOM file you want to attest.

Verifying artifact attestations with the GitHub CLI

To verify artifact attestations for binaries, use the following GitHub CLI command.

Bash
gh attestation verify PATH/TO/YOUR/BUILD/ARTIFACT-BINARY -R ORGANIZATION_NAME/REPOSITORY_NAME

To verify artifact attestations for container images, you must provide the image's FQDN prefixed with oci:// instead of the path to a binary. You can use the following GitHub CLI command.

Bash
docker login ghcr.io

gh attestation verify oci://ghcr.io/ORGANIZATION_NAME/IMAGE_NAME:test -R ORGANIZATION_NAME/REPOSITORY_NAME

For more information, see the attestation section of the GitHub CLI manual.