Getting started using the CLI

This tutorial shows how to configure and test a Binary Authorization policy that requires attestations. This type of policy secures your container-based software supply chain by defining who can deploy container images on Google Kubernetes Engine (GKE) and which container images are allowed to be deployed on GKE.

At deploy time, Binary Authorization uses attestors to verify digital signatures in attestations. The attestations were created by signers as part of a continuous integration (CI) pipeline.

In this tutorial, the GKE cluster, attestations, and attestors are all located in a single project. A single-project configuration is mostly useful for testing or experimenting with the service. For a more real-world example, see multi-project configuration.

The steps below describe tasks that you perform at the command line. To follow these steps using Google Cloud Console, see Getting Started Using the Console.

Objectives

In this tutorial, you learn how to:

  • Create a Google Kubernetes Engine (GKE) cluster with Binary Authorization enabled
  • Create an attestor that the Binary Authorization enforcer uses to verify the signature on an attestation
  • Configure a policy that requires an attestation
  • Create a cryptographic key pair to sign attestations and later verify them
  • Sign a container image digest, creating a signature
  • Create an attestation using the signature
  • Test the policy by deploying a container image to GKE

Costs

This tutorial uses billable components of Google Cloud, including:

  • Container Registry
  • GKE

Use the Pricing Calculator to generate a cost estimate based on your projected usage. New Cloud Platform users might be eligible for a free trial.

Before you begin

  1. Sign in to your Google Account.

    If you don't already have one, sign up for a new account.

  2. In the Cloud Console, on the project selector page, select or create a Cloud project.

    Go to the project selector page

  3. Make sure that billing is enabled for your Google Cloud project. Learn how to confirm billing is enabled for your project.

  4. Install and initialize the Cloud SDK.
  5. Install kubectl for interacting with GKE.

Enable Binary Authorization

Set the default project

The first step is to set the default Google Cloud project used by the gcloud command:

PROJECT_ID=PROJECT_ID
gcloud config set project ${PROJECT_ID}

where PROJECT_ID is the name of your project.

Enable required APIs

Next, enable the Google Cloud APIs for GKE, Container Analysis, and Binary Authorization:

gcloud services enable \
    container.googleapis.com \
    containeranalysis.googleapis.com \
    binaryauthorization.googleapis.com

Create a cluster with Binary Authorization enabled

Create the cluster

Now you can create a GKE cluster with Binary Authorization enabled. This is the cluster where you want your deployed container images to run. When you create the cluster, you pass the --enable-binauthz flag to the gcloud container clusters create command.

To create the cluster, follow these steps:

gcloud container clusters create \
    --enable-binauthz \
    --zone us-central1-a \
    test-cluster

Here, you create a cluster named test-cluster in the GKE zone us-central1-a.

Configure kubectl

You must also update the local kubeconfig file for your kubectl installation. This provides the credentials and endpoint information required to access the cluster in GKE.

To update the local kubeconfig file:

gcloud container clusters get-credentials \
    --zone us-central1-a \
    test-cluster

View the default policy

A policy in Binary Authorization is a set of rules that govern the deployment of container images. You can have one policy per project. By default, the policy is configured to allow all container images to be deployed.

Binary Authorization allows you to export and import a policy file in YAML format. This format reflects the structure of a policy as it is stored by the service. When you configure a policy using gcloud commands, you edit this file.

To view the default policy, export the policy YAML file:

gcloud container binauthz policy export

By default, the file has the following contents:

admissionWhitelistPatterns:
- namePattern: gcr.io/google_containers/*
- namePattern: gcr.io/google-containers/*
- namePattern: k8s.gcr.io/*
- namePattern: gke.gcr.io/*
- namePattern: gcr.io/stackdriver-agents/*
defaultAdmissionRule:
  evaluationMode: ALWAYS_ALLOW
  enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
name: projects/${PROJECT_ID}/policy

Here, the default rule is defined in the defaultAdmissionRule node. evaluationMode specifies that the policy allows all attempts at image deployment.

For more information on the structure of a policy, see the Policy YAML Reference.

Create an attestor

An attestor is the verification authority that the Binary Authorization enforcer uses at deploy time to decide whether to allow GKE to deploy the corresponding signed container image. The attestor contains the public key and is typically managed by personnel in your organization who are responsible for software supply chain security.

Creating an attestor requires you to:

  • Create a note in Container Analysis to store trusted metadata used in the authorization process
  • Create the attestor itself in Binary Authorization and associate the note you created

For this tutorial, you have one attestor named test-attestor and a Container Analysis note named test-attestor-note. In a real-world scenario, you can have any number of attestors, each one representing a party that participates in the authorization process for a container image.

Create the Container Analysis note

  1. Set variables that store the name of your attestor and Container Analysis note:

    ATTESTOR=test-attestor
    NOTE_ID=test-attestor-note
    
  2. Create a JSON file in /tmp/note_payload.json that describes the Container Analysis note:

    cat > /tmp/note_payload.json << EOM
    {
      "name": "projects/${PROJECT_ID}/notes/${NOTE_ID}",
      "attestation": {
        "hint": {
          "human_readable_name": "Attestor Note"
        }
      }
    }
    EOM
    
  3. Create the note by sending an HTTP request to the Container Analysis REST API:

    curl -X POST \
        -H "Content-Type: application/json" \
        -H "Authorization: Bearer $(gcloud auth print-access-token)"  \
        --data-binary @/tmp/note_payload.json  \
        "https://containeranalysis.googleapis.com/v1/projects/${PROJECT_ID}/notes/?noteId=${NOTE_ID}"
    
  4. Verify that the note was created:

    curl \
    -H "Authorization: Bearer $(gcloud auth print-access-token)" \
    "https://containeranalysis.googleapis.com/v1/projects/${PROJECT_ID}/notes/${NOTE_ID}"
    

Create the attestor

Now, you can create the attestor:

  1. Create the attestor in Binary Authorization:

    gcloud container binauthz attestors create ${ATTESTOR} \
    --attestation-authority-note=${NOTE_ID} \
    --attestation-authority-note-project=${PROJECT_ID}
    
  2. Verify that the attestor was created:

    gcloud container binauthz attestors list
    

The attestor you created is not yet usable without an associated PKIX key pair, which you create below.

Generate a key pair

Binary Authorization uses cryptographic keys to securely verify the identity of signers. This ensures that only authorized container images can be deployed. The key pair consists of a private key and a public key. The signer uses the private key to sign the container image digest, producing a signature that is then stored in an attestation. The public key is stored in the attestor. At deploy time, the Binary Authorization enforcer uses the attestor's public key to verify the signature in the attestation before allowing the container to deploy.

In this tutorial, you use Public-Key Infrastructure (X.509) (PKIX) format for cryptographic keys. This tutorial uses the recommended Elliptic Curve Digital Signing Algorithm (ECDSA) to generate a PKIX key pair. You can also use RSA or PGP keys for signing.

Key purposes and algorithms for more information on signing algorithms.

The keys generated and stored by Cloud Key Management Service (Cloud KMS) are PKIX-compliant. See Creating attestors using the CLI for more information on using PKIX keys and Cloud KMS.

To generate a PKIX key pair, follow these steps:

  1. Create the private key:

    PRIVATE_KEY_FILE="/tmp/ec_private.pem"
    openssl ecparam -genkey -name prime256v1 -noout -out ${PRIVATE_KEY_FILE}
    
  2. Extract the public key from the private key:

    PUBLIC_KEY_FILE="/tmp/ec_public.pem"
    openssl ec -in ${PRIVATE_KEY_FILE} -pubout -out ${PUBLIC_KEY_FILE}
    
  3. Add the ECDSA public key to the attestor.

    Now, add the public key you exported to the attestor so that it can be used by Binary Authorization for identity verification:

    gcloud --project="${PROJECT_ID}" \
        beta container binauthz attestors public-keys add \
        --attestor="${ATTESTOR}" \
        --pkix-public-key-file=${PUBLIC_KEY_FILE} \
        --pkix-public-key-algorithm=ecdsa-p256-sha256
    
  4. Save the public key ID.

    To save the public key ID, you can copy it from the output of public-keys add above. To view your attestor's public key ID after adding it to the attestor, use gcloud container binauthz attestors describe ${ATTESTOR}:

    PUBLIC_KEY_ID=$(gcloud container binauthz attestors describe ${ATTESTOR} \
      --format='value(userOwnedGrafeasNote.publicKeys[0].id)')
    

Configure the policy

Now, you can configure your policy. In this step, you export the policy YAML file to your local system and modify the default rule so that it requires an attestation by the attestor you defined above.

To configure the policy, follow these steps:

  1. Create a new policy file that sets the evaluationMode to REQUIRE_ATTESTATION and adds a node named requireAttestationsBy that references the attestor you created:

    cat > /tmp/policy.yaml << EOM
        admissionWhitelistPatterns:
        - namePattern: gcr.io/google_containers/*
        - namePattern: gcr.io/google-containers/*
        - namePattern: k8s.gcr.io/*
        - namePattern: gke.gcr.io/*
        - namePattern: gcr.io/stackdriver-agents/*
        defaultAdmissionRule:
          evaluationMode: REQUIRE_ATTESTATION
          enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
          requireAttestationsBy:
            - projects/${PROJECT_ID}/attestors/${ATTESTOR}
        name: projects/${PROJECT_ID}/policy
    EOM
    
  2. Import the policy YAML file into Binary Authorization:

    gcloud container binauthz policy import /tmp/policy.yaml
    

For more information on configuring a policy, see Configuring a Policy Using the CLI.

Test the policy

You can test the policy you configured above by trying to deploy a sample container image to the cluster. The policy will block deployment because the required attestation has not been made.

For this tutorial, you can use the sample image located at the path gcr.io/google-samples/hello-app in Container Registry. This is a public container image created by Google that contains a Hello, World! sample application.

First, try to deploy the image:

kubectl run hello-server --image gcr.io/google-samples/hello-app:1.0 --port 8080

Now, verify that the deployment was blocked by Binary Authorization:

kubectl get pods

The command prints the following message, which indicates that the image was not deployed:

No resources found.

You can get further details about the deployment:

kubectl get event --template \
'{{range.items}}{{"\033[0;36m"}}{{.reason}}:{{"\033[0m"}}\{{.message}}{{"\n"}}{{end}}'

which shows that the deployment was disallowed by the policy:

FailedCreate: Error creating: pods "hello-server-579859fb5b-hjvnr" is forbidden: image policy webhook backend denied one or more images: Denied by default admission rule. Denied by Attestation Authority. Image gcr.io/google-samples/hello-app:1.0 denied by projects/example-project/attestors/test-attestor: No attestations found

Make sure to delete the deployment so you can continue to the next step:

kubectl delete deployment hello-server

Create an attestation

An attestation is a digital document created by a signer that certifies that GKE is allowed to deploy the associated container image. The process of creating an attestation is sometimes called "signing an image." A signer can be a person or, more often, an automated process that runs when a container image is built. The signature is created using the private key from a key pair. At deploy time, the Binary Authorization enforcer uses the attestor's public key to verify the signature in the attestation.

In this tutorial, your attestation simply states that you authorize the image for deployment.

To create an attestation, follow these steps:

  1. Set variables that store the registry path and digest of the image:

    IMAGE_PATH="gcr.io/google-samples/hello-app"
    IMAGE_DIGEST="sha256:c62ead5b8c15c231f9e786250b07909daf6c266d0fcddd93fea882eb722c3be4"
    
  2. Generate the attestation payload:

    gcloud container binauthz create-signature-payload \
    --artifact-url=${IMAGE_PATH}@${IMAGE_DIGEST} > /tmp/generated_payload.json
    

    The payload JSON file has the following contents:

    {
      "critical": {
        "identity": {
          "docker-reference": "gcr.io/google-samples/hello-app"
        },
        "image": {
          "docker-manifest-digest": "sha256:c62ead5b8c15c231f9e786250b07909daf6c266d0fcddd93fea
    882eb722c3be4"
        },
        "type": "Google cloud binauthz container signature"
      }
    }
    
  3. Sign the payload with your PKIX private key and output a signature file:

    openssl dgst -sha256 -sign ${PRIVATE_KEY_FILE} /tmp/generated_payload.json > /tmp/ec_signature
    

    The signature file is a digitally-signed version of the payload JSON file you created above.

  4. Create and validate the attestation:

    This command creates the attestation. The --validate parameter causes the command to validate the attestation against the associated attestor, ensuring that the --artifact-url parameter is well formed.

    gcloud alpha container binauthz attestations create \
        --artifact-url="${IMAGE_PATH}@${IMAGE_DIGEST}" \
        --attestor="projects/${PROJECT_ID}/attestors/${ATTESTOR}" \
        --signature-file=/tmp/ec_signature \
        --public-key-id="${PUBLIC_KEY_ID}" \
        --validate
    

    where PUBLIC_KEY_ID is the public key id that you found in Generate a PKIX key pair above.

  5. Verify that the attestation was created:

    gcloud container binauthz attestations list \
        --attestor=$ATTESTOR --attestor-project=$PROJECT_ID
    

For more information on creating attestations, see Creating Attestations.

Retest the policy

Again, test the policy by deploying a sample container image to the cluster. This time, you must deploy the image using the digest rather than a tag like 1.0 or latest, as Binary Authorization will use both the image path and digest to look up attestations. Here, Binary Authorization allows the image to be deployed because the required attestation has been made.

To deploy the image, follow these steps:

kubectl run --generator=run-pod/v1 hello-server --image ${IMAGE_PATH}@${IMAGE_DIGEST} --port 8080

To verify that the image was deployed:

kubectl get pods

The command prints a message similar to the following, which indicates that deployment was successful:

NAME                            READY     STATUS    RESTARTS   AGE
hello-server-579859fb5b-h2k8s   1/1       Running   0          1m

Cleaning up

To avoid incurring charges to your Google Cloud Platform account for the resources used in this tutorial:

Delete the cluster you created in GKE:

gcloud container clusters delete \
    --zone=us-central1-a \
    test-cluster

What's next