Use customer-managed encryption keys (CMEK)

This page describes how to perform tasks related to customer-managed encryption keys (CMEK) for Firestore. For more information about CMEK in general, including when and why to enable it, see the Cloud KMS documentation.

Prepare your CMEK keys

Before you can create a CMEK-protected Firestore database, you must complete the following steps:

Request access to the Firestore CMEK feature.
Create (or retrieve) a Firestore service agent.
Create a CMEK key.
Configure IAM settings for that key.

Complete these steps for each project that will contain CMEK-protected Firestore databases. If you later create a new CMEK key, you must configure IAM settings for that key.

Request access

Before you create a Firestore service agent, request access to the CMEK feature by filling in this form.

Create a Firestore service agent

Before you create a CMEK key, you must have a Firestore service agent, which is a type of Google-managed service account that Firestore uses to access the key.

Run the services identity create command to create the service agent that Firestore uses to access the CMEK key on your behalf. This command creates the service account if it does not already exist, then displays it.

gcloud beta services identity create \
    --service=firestore.googleapis.com \
    --project FIRESTORE_PROJECT

Replace FIRESTORE_PROJECT with the project you plan to use for your Firestore databases.

The command displays the service agent ID, which is formatted like an email address. Record the output email string, because you'll use it in a later step.

Service identity created:
service-xxx@gcp-sa-firestore.iam.gserviceaccount.com

Create a key

You can use a key created directly in Cloud KMS or an externally managed key that you make available with Cloud External Key Manager.

The Cloud KMS key location must be the same as the location of the Firestore database that it will be used with.

For regional database locations, use the same location name for key ring, key, and database because the location names have a one-to-one mapping.

For example, if you want to create a CMEK-protected database in us-west1, create a key ring and key in us-west1.
For multi-region database locations, use the location name of the KMS multi-region location:
- Use the Cloud KMS us multi-region location for the Firestore nam5 multi-region location.
- Use the Cloud KMS europe multi-region location for the Firestore eur3 multi-region location.

In the Google Cloud project where you want to manage your keys, complete the following:

Enable the Cloud KMS API.
Create a key ring and a key using one of the following options:
- Create the key ring and key directly in Cloud KMS.
- Use an externally managed key. Create the external key and then create an Cloud EKM key to make the key available through Cloud KMS.

Configure IAM settings for the key

Console

To grant an Cloud KMS role to your service agent, do the following. You are also able to grant permission at the key or key-ring level if you want lower granularity.

In the Google Cloud console, go to the IAM page.

Go to the IAM page
Click Add.
Enter the email-formatted ID for your Firestore service agent.
Select the Cloud KMS CryptoKey Encrypter/Decrypter role.
Click Save.

gcloud

Grant the cloudkms.cryptoKeyEncrypterDecrypter role to your service agent:

gcloud kms keys add-iam-policy-binding KMS_KEY \
--keyring KMS_KEYRING\
--location KMS_LOCATION \
--member serviceAccount:SERVICE_AGENT_EMAIL \
--role roles/cloudkms.cryptoKeyEncrypterDecrypter \
--project KMS_PROJECT

Replace the following:

KMS_KEY with the name that you assigned to the key
KMS_KEYRING with the KMS key ring that contains the key
KMS_LOCATION with the region that contains the key ring
SERVICE_AGENT_EMAIL with the email-formatted identifier for the service agent that you are granting access to
KMS_PROJECT with the project that contains the key

The terminal should display a response similar to the following:

Updated IAM policy for key KMS_KEY.
bindings:
- members:
- serviceAccount:
service-{project-number}@gcp-sa-firestore.iam.gserviceaccount.com
role: roles/cloudkms.cryptoKeyEncrypterDecrypter

Create a CMEK-enabled database

After your CMEK keys are created and configured, you can create a CMEK-protected database. Existing Firestore databases that are protected by Google default encryption can't be converted to use CMEK.

You can choose an encryption type and key only when you create a CMEK-enabled database.

Console

In the Google Cloud console, go to the Databases page.

Go to the Databases page
Click Create Database.
Select your database mode. Click Continue.
On the Configure your database page, enter a database ID.
Select a location.
Click Show Encryption Options, and then select Cloud KMS key.
Select or enter the resource name for the CMEK key that you want to use for the database.

Note: You can't add or change the CMEK key later.
The list of keys is limited to the current Google Cloud project and the database location that you selected. To use a key from a different Google Cloud project, click Switch Project or Enter Key Manually.
If you are prompted to grant key permission to the Firestore service account, click Grant. To create a CMEK database, your Firestore service account must be granted the cloudkms.cryptoKeyEncrypterDecrypter role.
Select security rules for mobile and web clients.
Click Create Database.

Once the database is created, you can verify that the database is CMEK-enabled by viewing Database details:

If your database is protected by CMEK, the Encryption type field shows as Customer-managed and the Encryption key field lists the corresponding Cloud KMS and the key version that is used to protect this database.
If your database is not protected by CMEK, the Encryption type field shows as Google-managed.

gcloud

Before you create a CMEK-enabled database with Google Cloud CLI, install the latest version and authorize the gcloud CLI. For more information, see Install the gcloud CLI.

gcloud firestore databases create --location=FIRESTORE_DATABASE_LOCATION \
      --database=DATABASE_ID \
      --kms-key-name=KMS_KEY_NAME \
      --project=FIRESTORE_PROJECT

Replace the following:

FIRESTORE_DATABASE_LOCATION with the Firestore location for the database
DATABASE_ID with an ID for the database
KMS_KEY_NAME with the name you assigned to the key. Use the full resource name for the key in the following format:

projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID
FIRESTORE_PROJECT with the project to use for your Firestore database

REST API

HTTP request:

POST https://firestore.googleapis.com/v1/projects/{FIRESOTRE_PROJECT}/databases

In the request body configure CMEK in the cmek_config.kms_key_name field.

Set to the full resource ID of a Cloud KMS key. Only a key in the same location as this database is allowed.

This value should be the Cloud KMS key resource ID in the format of projects/{KMS_PROJECT}/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}

For more details for other fields, see the database create page.

Example request:

curl -X POST 'https://firestore.googleapis.com/v1/projects/FIRESTORE_PROJECT/databases?databaseId={DATABASE_ID}' \
-H "Authorization: Bearer $(gcloud auth print-access-token)" \
-H "Content-type: application/json" \
-d '{
  "type":"FIRESTORE_NATIVE",
  "locationId":"{FIRESTORE_DATABASE_LOCATION}",
  "cmekConfig": {
    "kmsKeyName":"projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID"
  }
}'

Firebase CLI

To create a CMEK-enabled database, use the KMS Key Name field. If you don't specify the --kms-key-name parameter, Firestore creates a non-CMEK database by default.

firebase firestore:databases:create DATABASE_ID
--location LOCATION
--kms-key-name projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID
--project FIRESTORE_PROJECT

Replace the following:

DATABASE_ID with the ID of your database
LOCATION with the location of your database
KMS_PROJECT with the project that contains your CMEK key
KMS_LOCATION with the location that contains your CMEK key and key ring
KMS_KEYRING_ID with the ID of your CMEK key ring
FIRESTORE_PROJECT with the project to use for your Firestore database

Confirm that your Firestore database is protected with Firebase CLI:

firebase firestore:databases:get DATABASE_ID --project FIRESTORE_PROJECT

The following CMEK information appears in the response message:

The KMS Key Name field provides the full key resource name that is used to encrypt your Firestore CMEK database.
The Active Key Versions field provides a list of all key versions currently used by this CMEK database. During key rotation, you can have multiple active key versions.

Terraform

To create a CMEK-enabled database, use the google_firestore_database resource. For more information and examples, see google_firestore_database.

resource "google_firestore_database" "database" {
  project     = "FIRESTORE_PROJECT"
  name        = "DATABASE_ID"
  location_id = "FIRESTORE_DATABASE_LOCATION"
  type        = "DATABASE_TYPE"

  cmek_config {
    kms_key_name = "KMS_KEY_NAME"
  }

}

Replace the following:

FIRESTORE_PROJECT with the project to use for your Firestore database
DATABASE_ID with an ID for the database
FIRESTORE_DATABASE_LOCATION with the Firestore location for the database
DATABASE_TYPE with either FIRESTORE_NATIVE for Native mode or DATASTORE_MODE for Datastore mode.
KMS_KEY_NAME with the name you assigned to the key. Use the full resource name for the key in the format of:

projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID

Access a CMEK-protected database

All the read, write, and query operations sent to a CMEK-protected database should function the same as with a Google default encrypted database. For example, you don't need to provide a key for each request.

Restore a CMEK-protected database

Before you restore CMEK-protected database from a backup:

Decide if you want to restore the database to CMEK encryption, to Google's default encryption (non-CMEK), or to the same encryption as the backup.
Prepare the key (primary-version) and the key version that you used to encrypt the backup. Enable both the key and the key version.

gcloud

Restore a CMEK-protected database to CMEK encryption

To restore to CMEK encryption, run the gcloud firestore databases restore command with the optional encryption-type and kms-key-name flags to configure the encryption type for the restored database. If you don't specify the encryption type, the restored database will use the same encryption configuration as the backup.

  gcloud firestore databases restore
  --encryption-type=customer-managed-encryption
  --kms-key-name=KMS_KEY_NAME

Replace KMS_KEY_NAME with the name that you assigned to the key. Use the full resource name for the key in the following format:

projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID

Restore a CMEK-protected database to default encryption

To restore to Google's default encryption (non-CMEK), set the encryption-type flag in the following way:

  gcloud firestore databases restore
  --encryption-type=google-default-encryption

Restore a CMEK-protected database to the same encryption type as the backup

To restore to the same encryption type as the backup, set the encryption-type flag in the following way:

  gcloud firestore databases restore --encryption-type=use-source-encryption

Firebase CLI

Restore a CMEK-protected database to CMEK encryption

To restore to CMEK encryption, use the optional encryption-type and kms-key-name flag. If you don't specify the encryption type, the restored database will use the same encryption configuration as the backup.

firebase firestore:databases:restore \
--database DATABASE_ID \
--backup 'projects/FIRESTORE_PROJECT/locations/FIRESTORE_LOCATION/backups/BACKUP_ID' \
--encryption-type CUSTOMER_MANAGED_ENCRYPTION \
--kms-key-name projects/KMS_PROJECT/locations/KMS_LOCATION/keyRings/KMS_KEYRING_ID/cryptoKeys/KMS_KEY_ID \
--project FIRESTORE_PROJECT

Replace the following:

DATABASE_ID with the ID of your database
FIRESTORE_PROJECT with the project to use for your Firestore database
FIRESTORE_LOCATION with the location of your Firestore database
BACKUP_ID with the ID of your backup
KMS_PROJECT with the project that contains your CMEK key
KMS_LOCATION with the location that contains your CMEK key and key ring
KMS_KEYRING_ID with the ID of your CMEK key ring

Confirm that your restored Firestore database is CMEK-encrypted:

firebase firestore:databases:get DATABASE_ID --project FIRESTORE_PROJECT

Restore a CMEK-protected database to default encryption

To restore to Google's default encryption (non-CMEK), set the encryption-type flag in the following way:

firebase firestore:databases:restore \
--database DATABASE_ID \
--backup 'projects/FIRESTORE_PROJECT/locations/FIRESTORE_LOCATION/backups/BACKUP_ID' \
--encryption-type GOOGLE_DEFAULT_ENCRYPTION \
--project FIRESTORE_PROJECT

Replace the following:

DATABASE_ID with the ID of your database
FIRESTORE_PROJECT with the project to use for your Firestore database
FIRESTORE_LOCATION with the location of your Firestore database
BACKUP_ID with the ID of your backup

Restore a CMEK-protected database to the same encryption type as the backup

To restore to the same encryption type as the backup, set the encryption-type flag in the following way:

firebase firestore:databases:restore \
--database DATABASE_IDD \
--backup 'projects/FIRESTORE_PROJECT/locations/FIRESTORE_LOCATION/backups/BACKUP_ID' \
--encryption-type USE_SOURCE_ENCRYPTION

Replace the following:

DATABASE_ID with the ID of your database
FIRESTORE_PROJECT with the project to use for your Firestore database
FIRESTORE_LOCATION with the location of your Firestore database
BACKUP_ID with the ID of your backup

View the key in use

gcloud

You can use the databases describe gcloud CLI command to confirm database CMEK configuration:

gcloud firestore databases describe --database=DATABASE_ID --project=FIRESTORE_PROJECT

You should see CMEK information in the cmekConfig field in the response similar to the following:

cmekConfig:
    activeKeyVersion:
    - projects/PROJECT_ID/locations/us/keyRings/KEYRING_NAME/cryptoKeys/KEY_NAME/cryptoKeyVersions/1
    kmsKeyName: projects/PROJECT_ID/locations/us/keyRings/KEYRING_NAME/cryptoKeys/KEY_NAME
  locationId: nam5
  name: projects/PROJECT_ID/databases/DATABASE_ID

The response includes the following information:

kmsKeyName: the full key resource name of the key that's used to encrypt your CMEK-protected database.
activeKeyVersion: a list of all key versions currently in use by the CMEK-protected database. During key rotation, you can have multiple active key versions. Both the old key version and new key version need to be available during key rotation. Don't disable the old key version until it no longer appears in the activeKeyVersion field.

REST API

HTTP request:

GET https://firestore.googleapis.com/v1/{name=projects/FIRESTORE_PROJECT/databases/DATABASE_ID}

In the request body configure CMEK in the cmek_config.kms_key_name field. Set to the full resource ID of a Cloud KMS key. Only a key in the same location as this database is allowed.

This value should be the Cloud KMS key resource ID in the format of projects/{KMS_PROJECT}/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}

For more details for other fields, see the database create page.

Example request and response:

curl 'https://firestore.googleapis.com/v1/projects/FIRESTORE_PROJECT/databases/{DATABASE_ID}' \
-H "Authorization: Bearer $(gcloud auth print-access-token)" \
-H "Content-type: application/json"

—----------------------------------------- Response —--------------------------------------------
{
  "name": "projects/FIRESTORE_PROJECT/databases/{DATABASE_ID}",
  "locationId": "{FIRESTORE_DATABASE_LOCATION}",
  "type": "FIRESTORE_NATIVE",
  "cmekConfig": {
    "kmsKeyName": "projects/{KMS_PROJECT}/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}",
    "activeKeyVersion": [
      "projects/{KMS_PROJECT}/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}/cryptoKeyVersions/1"
    ]
  },
  ……
}

Disable a key

To disable a key associated with a database, complete the following:

View the key versions in use for a database
Disable those key versions
Wait for the change to take effect and check if the data is no longer accessible. Changes typically take effect within minutes, but can take up to 3 hours.

When a key used by a database is disabled, expect to receive a FAILED_PRECONDITION exception with additional details in the error message, for example:

{
  "error": {
    "code": 400,
    "message": "The customer-managed encryption key required by the requested resource is not accessible. Error reason:  generic::permission_denied: Permission 'cloudkms.cryptoKeyVersions.useToEncrypt' denied on resource 'projects/FIRESTORE_PROJECT/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}' (or it may not exist).",
    "status": "FAILED_PRECONDITION",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.DebugInfo",
        "detail": "The customer-managed encryption key required by the requested resource is not accessible. Error reason:  generic::permission_denied: Permission 'cloudkms.cryptoKeyVersions.useToEncrypt' denied on resource 'projects/FIRESTORE_PROJECT/locations/{KMS_LOCATION}/keyRings/{KMS_KEYRING_ID}/cryptoKeys/{KMS_KEY_ID}' (or it may not exist)"
      }
    ]
  }
}

Enable a key

To re-enable a key associated with a database, complete the following:

View the key versions in use for a database
Enable those key versions
Wait for the change to take effect and check if the data is no longer accessible. Changes typically take effect within minutes, but can take up to 3 hours.

View audit logs for a Cloud KMS key

Before you enable Cloud KMS Data Access audit logs, you should be familiar with Cloud Audit Logs.

Cloud KMS Data Access audit logs show you when Firestore or any other products that are configured to use your CMEK key make encrypt/decrypt calls to Cloud KMS. Firestore does not issue an encrypt/decrypt call on every data request, but instead maintains a poller that checks the key periodically. The polling results appear in the audit logs.

You can set up and interact with the audit logs in the Google Cloud console:

Make sure that logging is enabled for the Cloud KMS API in your project.
Go to Cloud Logging in the Google Cloud console.

Go to Cloud Logging

Limit the log entries to your Cloud KMS key by adding the following lines to the Query builder:

resource.type="cloudkms_cryptokey"
resource.labels.key_ring_id = KMS_KEYRING
resource.labels.crypto_key_id = KMS_KEY
resource.labels.location=KMS_LOCATION

Replace the following:

KMS_KEY with the name of the CMEK key
KMS_KEYRING with the KMS key ring that contains the key
KMS_LOCATION with the location of the key and key ring

The log shows a couple log entries about every five minutes per database. The log entries look similar to these examples:

Info 2021-03-20 08:02:24.869 EDT Cloudkms.googleapis.com Decrypt projects/cloud-kms-project/locations/us-central1/keyRings/firestore-keys/cryptoKeys/my-cmek-key service-123456789123@gcp-sa-firestore.iam.gserviceaccount.com
audit_log, method: "Decrypt", principal_email: "service-1234567891011@gcp-sa-firestore.iam.gserviceaccount.com"

Info 2021-03-20 08:02:24.913 EDT Cloudkms.googleapis.com Encrypt projects/cloud-kms-project/locations/us-central1/keyRings/firestore-keys/cryptoKeys/my-cmek-key service-123456789123@gcp-sa-firestore.iam.gserviceaccount.com
audit_log, method: "Encrypt", principal_email: "service-123456789123@gcp-sa-firestore.iam.gserviceaccount.com"

See Understanding audit logs for details about interpreting audit logs.

Configure a CMEK organization policy

To specify encryption compliance requirements for Firestore databases in your organization, use a CMEK organization policy constraint.

Require CMEK protection

Configure constraints/gcp.restrictNonCmekServices to require CMEK for Firestore database creation. Set the constraint to deny and add firestore.googleapis.com to the deny list, for example:

 gcloud resource-manager org-policies deny gcp.restrictNonCmekServices  is:firestore.googleapis.com --project=FIRESTORE_PROJECT

Replace FIRESTORE_PROJECT with the project to restrict.

To learn more about configuring organization policies, see Creating and editing policies.

After the policy takes effect, you receive a FAILED_PRECONDITION exception and error message if you try to create a non-CMEK database under the affected project. For example, an exception looks like:

{
  "error": {
    "code": 400,
    "message": "Constraint 'constraints/gcp.restrictNonCmekServices' violated for 'projects/FIRESTORE_PROJECT' attempting to perform the operation 'google.firestore.admin.v1.FirestoreAdmin.CreateDatabase' with violated value 'firestore.googleapis.com'. See https://cloud.google.com/resource-manager/docs/organization-policy/org-policy-constraints for more information.",
    "status": "FAILED_PRECONDITION",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.PreconditionFailure",
        "violations": [
          {
            "type": "constraints/gcp.restrictNonCmekServices",
            "subject": "orgpolicy:projects/FIRESTORE_PROJECT",
            "description": "Constraint 'constraints/gcp.restrictNonCmekServices' violated for 'projects/FIRESTORE_PROJECT' attempting to perform the operation 'google.firestore.admin.v1.FirestoreAdmin.CreateDatabase' with violated value 'firestore.googleapis.com'. See https://cloud.google.com/resource-manager/docs/organization-policy/org-policy-constraints for more information."
          }
        ]

Limit the use of keys for CMEK

To limit which Cloud KMS keys are used for CMEK protection, configure the constraints/gcp.restrictCmekCryptoKeyProjects constraint.

As a list constraint, the accepted values are resource hierarchy indicators (for example, projects/PROJECT_ID, under:folders/FOLDER_ID, and under:organizations/ORGANIZATION_ID). Use this constraint by configuring a list of resource hierarchy indicators and setting the constraint to Allow. This configuration restricts supported services so that CMEK keys can be chosen only from the listed projects, folders, and organizations. Requests to create CMEK-protected resources in configured services don't succeed without a Firestore key from one of the allowed resources.

The following example allows only keys from the ALLOWED_KEY_PROJECT_ID for CMEK-protected databases in the specified project:

gcloud resource-manager org-policies allow gcp.restrictCmekCryptoKeyProjects \
under:projects/ALLOWED_KEY_PROJECT_ID \
--project=FIRESTORE_PROJECT

After the policy takes effect, you receive a FAILED_PRECONDITION exception and an error message if you violate the constraint. An exception looks like the following:

{
  "error": {
    "code": 400,
    "message": "Constraint 'constraints/gcp.restrictCmekCryptoKeyProjects' violated for 'projects/FIRESTORE_PROJECT' attempting to perform the operation 'google.firestore.admin.v1.FirestoreAdmin.CreateDatabase' with violated value 'projects/{NOT_ALLOWED_KEY_PROJECT}'. See https://cloud.google.com/resource-manager/docs/organization-policy/org-policy-constraints for more information.",
    "status": "FAILED_PRECONDITION",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.PreconditionFailure",
        "violations": [
          {
            "type": "constraints/gcp.restrictCmekCryptoKeyProjects",
            "subject": "orgpolicy:projects/FIRESTORE_PROJECT",
            "description": "Constraint 'constraints/gcp.restrictCmekCryptoKeyProjects' violated for 'projects/FIRESTORE_PROJECT' attempting to perform the operation 'google.firestore.admin.v1.FirestoreAdmin.CreateDatabase' with violated value 'projects/{NOT_ALLOWED_KEY_PROJECT}'. See https://cloud.google.com/resource-manager/docs/organization-policy/org-policy-constraints for more information."
          }
        ]
      }
    ]
  }
}

What's next

Read the overview of Firestore and CMEK