Use encrypted credentials from Cloud KMS

Cloud Key Management Service is a Google Cloud service that enables you to manage and use cryptographic keys. This page explains how to use encrypted information from Cloud KMS in Cloud Build.

Note: Secret Manager is the recommended technique for managing sensitive data with Cloud Build. For existing projects, you can continue using Cloud KMS, but for new projects, use Secret Manager. For instructions on configuring builds to access secrets from Secret Manager, see Using secrets from Secret Manager.

Before you begin

• Enable the Cloud Build and Cloud KMS APIs.

  Enable the APIs

• To use the command-line examples in this guide, install and configure the Google Cloud CLI.

  Note: If you've installed gcloud CLI previously, make sure you have the latest available version by running gcloud components update.

• Encrypt the sensitive information using Cloud KMS. Cloud KMS saves your encrypted content in a file.

• [OPTIONAL] To configure builds to use encrypted data, convert the ENCRYPTED_FILE to base64 (this step is not required for build configs that use encrypted files):

      base64 ENCRYPTED_FILE
  

Required IAM permissions

Grant the Cloud KMS CryptoKey Decrypter (roles/cloudkms.cryptoKeyDecrypter) IAM role to the build service account:

1. In the Google Cloud console, go to the Cloud Build Settings page:

   Open the Settings page

2. Locate the row with the Cloud KMS CryptoKey Decrypter role and set its Status to ENABLED.

Warning: Granting the Cloud KMS CryptoKey Decrypter role to the default Cloud Build service account allows the service account to decrypt the encrypted information. Build triggers use the default Cloud Build service account to execute builds. Therefore, any user who uses build triggers to run builds will have permissions granted to the service account at build time. This allows users without the CryptoKey Decrypter role to use build triggers to perform a build that decrypts the encrypted information. This action is logged in the project's build history.

Configuring builds to use encrypted data

1. In your project root directory, create a Cloud Build build config file named cloudbuild.yaml or cloudbuild.json.

2. In your build config file:

   • After all the build steps, add an availableSecrets field to specify the encrypted value as an environment variable and the kmsKeyName to use to decrypt it. You can use substitution variables in the value of kmsKeyName.
   • In the build step where you want to specify the secret:
     • Add an entrypoint field pointing to bash to use the bash tool in the build step. This is required to refer to the environment variable for the secret.
     • Add a secretEnv field specifying the environment variable for the encrypted value.
     • In the args field, add a -c flag as the first argument. Any string you pass after -c is treated as a command. For more information on running bash commands with -c, see the bash documentation.
     • When specifying the encrypted value in the args field, specify it using the environment variable prefixed with $$.
   Note: You can refer to encrypted values using environment variables only in the args field of a build step.

   The following example build config file shows how to login to Docker and pull a private image:

   YAML

    steps:
    - name: 'gcr.io/cloud-builders/docker'
      entrypoint: 'bash'
      args: ['-c', 'docker login --username=$$USERNAME --password=$$PASSWORD']
      secretEnv: ['USERNAME', 'PASSWORD']
    - name: 'gcr.io/cloud-builders/docker'
      entrypoint: 'bash'
      args: ['-c', 'docker pull $$USERNAME/IMAGE:TAG']
      secretEnv: ['USERNAME']
    availableSecrets:
      inline:
      - kmsKeyName: projects/PROJECT_ID/locations/global/keyRings/USERNAME_KEYRING_NAME/cryptoKeys/USERNAME_KEY_NAME
        envMap:
          USERNAME: 'ENCRYPTED_USERNAME'
      - kmsKeyName: projects/PROJECT_ID/locations/global/keyRings/PASSWORD_KEYRING_NAME/cryptoKeys/PASSWORD_KEY_NAME
        envMap:
          PASSWORD: 'ENCRYPTED_PASSWORD'
   

   JSON

   {
     "steps": [
     {
       "name": "gcr.io/cloud-builders/docker",
       "entrypoint": "bash",
       "args": [
         "-c",
         "docker login --username=$$USERNAME --password=$$PASSWORD"
       ],
       "secretEnv": [
         "USERNAME",
         "PASSWORD"
       ]
     },
     {
       "name": "gcr.io/cloud-builders/docker",
       "entrypoint": "bash",
       "args": [
         "-c",
         "docker pull $$USERNAME/REPOSITORY:TAG"
        ],
        "secretEnv": [
         "USERNAME"
       ]
     }
     ],
     "availableSecrets": {
       "inline": [{
         "kmsKeyName":  "projects/PROJECT_ID/locations/global/keyRings/USERNAME_KEYRING_NAME/cryptoKeys/USERNAME_KEY_NAME",
         "envMap": {
           "USERNAME": "ENCRYPTED_USERNAME"
          }
      },
      {
       "kmsKeyName": "projects/PROJECT_ID/locations/global/keyRings/PASSWORD_KEYRING_NAME/cryptoKeys/PASSWORD_KEY_NAME",
       "envMap": {
           "PASSWORD": "ENCRYPTED_PASSWORD"
          }
      }]
    }
   }
   

   Replace the placeholder values in the above commands with the following:

   • PROJECT_ID: The ID of the Google Cloud project which contains your Cloud KMS service.
   • USERNAME_KEYRING_NAME: The key ring name of your Docker username.
   • USERNAME_KEY_NAME: The key name of your Docker username.
   • ENCRYPTED_USERNAME: Your encrypted Docker username in base64 format.
   • PASSWORD_KEYRING_NAME: The key ring name of your Docker password.
   • PASSWORD_KEY_NAME: The key name of your Docker password.
   • ENCRYPTED_PASSWORD: Your encrypted Docker password in base64 format.
   • REPOSITORY: The name of your Docker repository from where you're pulling the image.

   • TAG: The tag name of your image.

     Note: The secretEnv field does not support substitution variables. If the Google Cloud project hosting the key changes, the encrypted contents within that project also change.

3. Use the build config file to manually start a build or to automate builds using triggers.

Configuring builds to use encrypted files

1. In your project root directory, create a Cloud Build build config file named cloudbuild.yaml or cloudbuild.json.

2. In your build config file, before any build steps that interact with the decrypted file, add a gcloud build step to decrypt the encrypted file using the encryption key. The following example build config file shows how to login to Docker using the encrypted file with Docker password:

   YAML

   steps:
   - name: gcr.io/cloud-builders/gcloud
     args:
     - kms
     - decrypt
     - "--ciphertext-file=ENCRYPTED_PASSWORD_FILE"
     - "--plaintext-file=PLAINTEXT_PASSWORD_FILE"
     - "--location=global"
     - "--keyring=KEYRING_NAME"
     - "--key=KEY_NAME"
   - name: gcr.io/cloud-builders/docker
     entrypoint: bash
     args:
     - "-c"
     - docker login --username=DOCKER_USERNAME --password-stdin < PLAINTEXT_PASSWORD_FILE
   

   JSON

   {
     "steps": [
     {
       "name": "gcr.io/cloud-builders/gcloud",
       "args": [
         "kms",
         "decrypt",
         "--ciphertext-file=ENCRYPTED_PASSWORD_FILE",
         "--plaintext-file=PLAINTEXT_PASSWORD_FILE",
         "--location=global",
         "--keyring=KEYRING_NAME",
         "--key=KEY_NAME"
       ]
     },
     {
       "name": "gcr.io/cloud-builders/docker",
       "entrypoint": "bash",
       "args": [
         "-c",
         "docker login --username=DOCKER_USERNAME --password-stdin < PLAINTEXT_PASSWORD_FILE"
       ]
      }
     ]
   }
   

   Replace the placeholder values in the above commands with the following:

   • KEYRING_NAME: The key ring name of your Docker password.
   • KEY_NAME: The key name of your Docker password.
   • ENCRYPTED_PASSWORD_FILE: Encrypted file with your Docker password.
   • PLAINTEXT_PASSWORD_FILE: Plaintext file with your Docker password.

3. Use the build config file to manually start a build or to automate builds using triggers.

Configuring builds to use encrypted data (legacy)

Warning: This is the legacy method of using Cloud KMS with Cloud Build. This method will continue to work, but we recommend that you use the newer way of configuring builds to use encrypted data.

To encrypt sensitive data using Cloud KMS and use that data in a build config file:

1. In your build config file, add a secrets field to specify the encrypted value and the CryptoKey to use to decrypt it. Then, in the build step where you want to use the encrypted variable, add a secretEnv field to specify the variable as an environment variable. Include the variable's name in the secretEnv field. If you specify the variable value, or a non-secret environment variable with the same name, Cloud Build throws an error.

   YAML

   steps:
   - name: 'gcr.io/cloud-builders/docker'
     entrypoint: 'bash'
     args: ['-c', 'docker login --username=user-name --password=$$PASSWORD']
     secretEnv: ['PASSWORD']
   - name: 'gcr.io/cloud-builders/docker'
     args: ['push', 'user-name/myubuntu']
   secrets:
   - kmsKeyName: projects/project-id/locations/global/keyRings/keyring-name/cryptoKeys/key-name
     secretEnv:
       PASSWORD: 'encrypted-password'
   

   JSON

   {
     "steps": [
     {
       "name": "gcr.io/cloud-builders/docker",
       "entrypoint": "bash",
       "args": [
         "-c",
         "docker login --username=user-name --password=$$PASSWORD"
       ],
       "secretEnv": [
         "PASSWORD"
        ]
      },
      {
        "name": "gcr.io/cloud-builders/docker",
        "args": [
          "push",
          "user-name/myubuntu"
         ]
      }
      ],
      "secrets": [
      {
        "kmsKeyName": "projects/project-id/locations/global/keyRings/keyring-name/cryptoKeys/key-name",
        "secretEnv": {
          "PASSWORD": "encrypted-password"
        }
      }
      ]
   }
   

What's next

• Learn how to configure builds to access secrets from Secret Manager.
• Learn how to access private GitHub repositories.