Creating attestors using the CLI

This page explains how to create an attestor in Binary Authorization at the the command line using gcloud commands. As an alternative, you can also perform these steps using the Google Cloud Platform Console or using the REST API. This task is part of setting up Binary Authorization.

Overview

An attestor is a party that is responsible for attesting that a required process has completed before a container image can be deployed. This party can be a human user or, more often, a machine process like a build and test system, or your continuous integration (CI) and deployment (CD) pipelines.

Creating an attestor requires you to:

Create a note in Container Analysis to store trusted metadata used in the attestation process.
Set up a PGP or PKIX key pair that can be used to verify the identity of the attestor. (Asymmetric key pairs generated by Cloud Key Management Service (Cloud KMS) are in PKIX-compatible format.)
Create the attestor itself in Binary Authorization, and associate the note and public key you created.

In a single-project setup, you create your attestor in the same Google Cloud Platform project where you configure your Binary Authorization policy. In a multi-project setup, you most likely have a deployer project where your policy is configured and a separate attestor project where your attestors are stored.

Set the default project

Set the default Google Cloud Platform project if you have not already done so:

PROJECT_ID=PROJECT_ID
gcloud config set project ${PROJECT_ID}

Set up the environment

Set up environment variables to store your project names and numbers:

DEPLOYER_PROJECT_ID=${PROJECT_ID}
DEPLOYER_PROJECT_NUMBER="$(
    gcloud projects describe "${DEPLOYER_PROJECT_ID}" \
      --format="value(projectNumber)"
)"
ATTESTOR_PROJECT_ID=${PROJECT_ID}
ATTESTOR_PROJECT_NUMBER="$(
    gcloud projects describe "${ATTESTOR_PROJECT_ID}" \
    --format="value(projectNumber)"
)"

If your attestor and deployer projects are the same project, use the same project ID for both variables.

You must also get the service account names for the projects:

DEPLOYER_SERVICE_ACCOUNT="service-${DEPLOYER_PROJECT_NUMBER}@gcp-sa-binaryauthorization.iam.gserviceaccount.com"
ATTESTOR_SERVICE_ACCOUNT="service-${ATTESTOR_PROJECT_NUMBER}@gcp-sa-binaryauthorization.iam.gserviceaccount.com"

Create a Container Analysis note

Binary Authorization uses Container Analysis to store trusted metadata used in the authorization process. For each attestor you create, you must create one Container Analysis note. Each attestation is stored as an occurrence of this note.

To create a Container Analysis note:

Set up environment variables to store the note ID and a human-readable description:
```
NOTE_ID=NOTE_ID
NOTE_URI="projects/${ATTESTOR_PROJECT_ID}/notes/${NOTE_ID}"
DESCRIPTION=DESCRIPTION
```
where:
- NOTE_ID is the internal name of the note in alphanumeric characters with no spaces (for example, test-attestor-note)
- NOTE_URI is the fully-qualified path to the note resource
- DESCRIPTION is a human-readable display name for the note (for example, Test Attestor Note)

In a text editor, create a JSON file in /tmp/note_payload.json that describes the Container Analysis note:

cat > /tmp/note_payload.json << EOM
{
  "name": "${NOTE_URI}",
  "attestation": {
    "hint": {
      "human_readable_name": "${DESCRIPTION}"
    }
  }
}
EOM

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)"  \
    -H "x-goog-user-project: ${ATTESTOR_PROJECT_ID}" \
    --data-binary @/tmp/note_payload.json  \
    "https://containeranalysis.googleapis.com/v1/projects/${ATTESTOR_PROJECT_ID}/notes/?noteId=${NOTE_ID}"

To verify that the note was created successfully:

curl \
    -H "Authorization: Bearer $(gcloud auth print-access-token)"  \
    -H "x-goog-user-project: ${ATTESTOR_PROJECT_ID}" \
    "https://containeranalysis.googleapis.com/v1/projects/${ATTESTOR_PROJECT_ID}/notes/"

Set permissions on the note

You must also set permissions on the Container Analysis note you created so that it is accessible to the attestor project service account. You do this by updating the IAM policy for the note to assign the containeranalysis.notes.occurrences.viewer role to the account.

To set the permissions:

Generate a JSON file that contains the information needed to set the IAM policy on your note:

cat > /tmp/iam_request.json << EOM
{
  "resource": "${NOTE_URI}",
  "policy": {
    "bindings": [
      {
        "role": "roles/containeranalysis.notes.occurrences.viewer",
        "members": [
          "serviceAccount:${ATTESTOR_SERVICE_ACCOUNT}"
        ]
      }
    ]
  }
}
EOM

Add the service account and requested access roles to the IAM policy for the note you created:

curl -X POST  \
    -H "Content-Type: application/json" \
    -H "Authorization: Bearer $(gcloud auth print-access-token)" \
    -H "x-goog-user-project: ${ATTESTOR_PROJECT_ID}" \
    --data-binary @/tmp/iam_request.json \
    "https://containeranalysis.googleapis.com/v1/projects/${ATTESTOR_PROJECT_ID}/notes/${NOTE_ID}:setIamPolicy"

Set up cryptographic keys

Binary Authorization allows you to use PGP key pairs or PKIX keys to securely verify the identity of attestors. This ensures that only verified parties can authorize a container image.

Create a PGP key pair

A PGP key pair consists of a private key, which you use to digitally sign attestations, and a public key, which you add to the attestor as stored by the Binary Authorization service.

To generate the key pair:

Install GnuPG 2.0 or later (gpgv2) for PGP key management.
Set up environment variables to store the name of the attestor and an e-mail address associated with the key pair:
```
ATTESTOR_NAME=ATTESTOR_NAME
ATTESTOR_EMAIL=ATTESTOR_EMAIL
```
where:
- ATTESTOR_NAME is the name of the attestor (for example, test-attestor)
- ATTESTOR_EMAIL is the e-mail address associated with the attestor (for example, attestor@example.com)

Run gpg --gen-key from the command line:

gpg --batch --gen-key <(
  cat <<- EOF
    Key-Type: RSA
    Key-Length: 2048
    Name-Real: "${ATTESTOR_NAME}"
    Name-Email: "${ATTESTOR_EMAIL}"
    %commit
EOF
)

Export the public key:

gpg --armor --export "${ATTESTOR_EMAIL}" > /tmp/generated-key.pgp

The exported public key is located in /tmp/generated-key.pgp. The private key is stored on the local system where you ran the gpg --gen-key command.

Create a PKIX key pair

Binary Authorization allows you to use asymmetric PKIX key pairs instead of PGP keys to verify the identity of an attestor. As with PGP keys, the key pair consists of a private key, which the attestor uses to digitally sign attestations, and a public key, which you add to the attestor as stored by the Binary Authorization service.

The asymmetric key pairs generated and stored in Cloud KMS are compliant with the PKIX format. To create a Cloud KMS key for use with Binary Authorization, see Creating Asymmetric Keys. Make sure that you choose Asymmetric Sign as the key purpose when you create the key.

To create a new local asymmetric PKIX key pair and store it in a file:

Generate the key:

KEY_FILE="/tmp/example.pem"
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out ${KEY_FILE}

Since this file contains a public and private key together, you need to extract the public key into a separate file so you can add it to the attestor:
```
PUBLIC_KEY_FILE="/tmp/example.pub"
openssl rsa -in ${KEY_FILE} -pubout -out ${PUBLIC_KEY_FILE}
```

Create the attestor

The next step is to create the attestor itself in Binary Authorization with the associated Container Analysis note. You must also add the cryptographic public key.

To create the attestor:

Set up an environment variable to store the name of the attestor as defined in Binary Authorization:
```
ATTESTOR=ATTESTOR
```
where ATTESTOR is the name of the attestor you want to create (for example, build-secure or prod-qa).

Create the attestor resource in Binary Authorization:

gcloud --project="${ATTESTOR_PROJECT_ID}" \
    beta container binauthz attestors create "${ATTESTOR}" \
    --attestation-authority-note="${NOTE_ID}" \
    --attestation-authority-note-project="${ATTESTOR_PROJECT_ID}"

Add an IAM role binding for the deployer project to the attestor. This is used by Binary Authorization when it evaluates a policy to determine whether the project has permissions to access any associated attestations.

gcloud container binauthz attestors add-iam-policy-binding \
  "projects/${ATTESTOR_PROJECT_ID}/attestors/${ATTESTOR}" \
  --member="serviceAccount:${DEPLOYER_SERVICE_ACCOUNT}" \
  --role=roles/binaryauthorization.attestorsVerifier

Add the public key to the attestor:

PGP

gcloud --project="${ATTESTOR_PROJECT_ID}" \
    beta container binauthz attestors public-keys add \
    --attestor="${ATTESTOR}" \
    --public-key-file=/tmp/generated-key.pgp

where /tmp/generated-key.pgp is the file to which you exported the public key above.

PKIX (Cloud KMS)

Set up environment variables to store information about the key pair as managed by Cloud KMS:
```
KMS_KEY_PROJECT_ID=KMS_KEY_PROJECT_ID
KMS_KEY_LOCATION=KMS_KEY_LOCATION
KMS_KEYRING_NAME=KMS_KEYRING_NAME
KMS_KEY_NAME=KMS_KEY_NAME
KMS_KEY_VERSION=KMS_KEY_VERSION
```
where:
- KMS_KEY_PROJECT_ID is the ID of the project where the keys are stored
- KMS_KEY_LOCATION is the location of the key
- KMS_KEYRING_NAME is the name of the key ring
- KMS_KEY_NAME is the name of the key
- KMS_KEY_VERSION is the key version