Protect resources by using Cloud KMS keys

By default, Compute Engine encrypts customer content at rest. Compute Engine handles and manages this encryption for you without any additional actions on your part. However, if you want to control and manage this encryption yourself, you can use key encryption keys. Key encryption keys do not directly encrypt your data but are used to encrypt the data encryption keys that encrypt your data.

You have two options for key encryption keys in Compute Engine:

After you create a Compute Engine resource that Cloud KMS helps to protect, you do not need to specify the key because Compute Engine knows which KMS key was used. This is different from how Compute Engine accesses resources that customer-supplied keys help to protect. For that access, you need to specify the customer-supplied key.

Learn more about encryption options on Google Cloud.

Before you begin

  1. Understand disks, images, persistent disk snapshots, and virtual machine (VM) instances.

  2. Decide whether you are going to run Compute Engine and Cloud KMS in the same Google Cloud project, or in different projects.

    For information about Cloud project IDs and project numbers, see Identifying projects.

  3. For the Cloud project that runs Compute Engine, set up API access for Compute Engine.

  4. For the Cloud project that runs Cloud KMS, do the following:

    1. Enable the Cloud KMS API.
    2. Create a key ring and a key as described in Creating key rings and keys.
  5. Assign the Cloud KMS CryptoKey Encrypter/Decrypter role to the Compute Engine Service Agent. This account has the following form:

    service-PROJECT_NUMBER@compute-system.iam.gserviceaccount.com
    

    You can use the gcloud command-line tool to assign the role:

    gcloud projects add-iam-policy-binding KMS_PROJECT_ID \
        --member serviceAccount:service-PROJECT_NUMBER@compute-system.iam.gserviceaccount.com \
        --role roles/cloudkms.cryptoKeyEncrypterDecrypter
    

    Replace the following:

    • KMS_PROJECT_ID: the ID of your Cloud project that runs Cloud KMS (even if this is the same project running Compute Engine)
    • PROJECT_NUMBER: the project number (not Cloud project ID) of your Cloud project that runs the Compute Engine resources

Limitations

  • Regional resources (disks) can be encrypted by keys in the same location or in the global location. For example, a disk in zone us-west1-a can be encrypted by a key in us-west1 or global. Global resources (images, snapshots) can be encrypted by keys in any location.

  • Encrypting a disk, snapshot, or image with a key is permanent. You cannot remove the encryption from the resource or change the key that is used. The only way to remove encryption or change keys is to create a copy of the resource while specifying a new encryption option.

Specifications

This section describes the encryption specification and the limitations of using Cloud KMS keys.

Encryption

Cloud KMS keys used to help protect your data in Compute Engine are AES-256 keys. These keys are key encryption keys, and they encrypt the data encryption keys that encrypt your data.

Restrictions

  • You can encrypt only new persistent disks, images, and snapshots with your own key. You cannot encrypt existing resources with your own key.

  • You cannot use your own keys with local SSDs because local SSDs do not persist beyond the life of a VM. Local SSDs receive protection through an ephemeral encryption key that Google does not retain.

Encrypt a new persistent disk with CMEK

You can encrypt a new persistent disk by supplying a key during VM or disk creation.

Console

  1. In the Google Cloud Console, go to the Disks page.

    Go to Disks

  2. Click Create disk and enter the properties for the new disk.
  3. Under Encryption, select Customer-managed key.
  4. In the drop-down menu, select the Cloud KMS key that you want to use to encrypt this disk.
  5. To create the disk, click Create.

gcloud

gcloud compute disks \
create encrypted-disk \
    --kms-key projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/KEY

Replace the following:

  • REGION: the region where the disk is located
  • KEY_RING: the name of the key ring that includes the key
  • KEY: the name of the key used to encrypt the disk

API

Encrypt a disk using the diskEncryptionKey property with the kmsKeyName property. For example, you can encrypt a new disk during VM creation with your Cloud KMS key by using the following:

POST
https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances

{
"machineType": "zones/ZONE/machineTypes/e2-standard-2",
"disks": [
 {
  "type": "PERSISTENT",
  "diskEncryptionKey": {
    "kmsKeyName": "projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/KEY"
  },
  "initializeParams": {
   "sourceImage": "projects/debian-cloud/global/images/debian-8-jessie-v20160301"
  },
  "boot": true
 }
],
...
}

Replace the following:

  • PROJECT_ID: the ID of the Cloud project running Compute Engine
  • ZONE: the zone to create the VM in
  • REGION: the region where the disk is located
  • KEY_RING: the name of the key ring that includes the key
  • KEY: the name of the key used to encrypt the disk

Similarly, you can also use the API to create a new stand-alone persistent disk and encrypt it with your Cloud KMS key:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/disks?sourceImage=https%3A%2F%2Fwww.googleapis.com%2Fcompute%2Fprojects%2Fdebian-cloud%2Fglobal%2Fimages%2Fdebian-8-jessie-v20160301

{
 "name": "new-encrypted-disk-key",
 "diskEncryptionKey": {
   "kmsKeyName": "projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/KEY"
  },
 "type": "zones/ZONE/diskTypes/pd-standard"
}

Create a snapshot from a disk encrypted with CMEK

To help protect a snapshot that you create from a disk encrypted with CMEK, you must use the same encryption key that you used to encrypt the disk.

Snapshots from disks encrypted with CMEK are incremental.

Console

  1. In the Google Cloud Console, go to the Snapshots page.

    Go to Snapshots

  2. Click Create snapshot.
  3. Under Source disk, choose the source disk for the snapshot. The snapshot is automatically encrypted with the same key used by the source disk.

gcloud

gcloud compute \
disks snapshot encrypted-disk \
    --zone ZONE

Replace ZONE with the zone to create the snapshot in.

API

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/disks/example-disk/createSnapshot

{
 "snapshotEncryptionKey":  {
   "kmsKeyName": "projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/SNAPSHOT_KEY"
 },
 "name": "snapshot-encrypted-disk"
}

Replace SNAPSHOT_KEY with the name of the key that is used to encrypt the source disk.

You cannot create a snapshot that uses a CMEK unless the source disk uses CMEK as well. Also, you cannot convert encrypted disks or encrypted snapshots to use Compute Engine default encryption unless you create a completely new disk image and a new persistent disk.

Encrypt an imported image with CMEK

You can encrypt a new image when you import a custom image to Compute Engine. Before you can import an image, you must create and compress a disk image file and upload that compressed file to Cloud Storage.

Console

  1. In the Google Cloud Console, go to the Images page.

    Go to Images

  2. Click Create image.
  3. For Source disk, select the disk you want to create an image of.
  4. For Encryption, select Customer-managed key.
  5. In the drop-down menu, select the Cloud KMS key that you want to use to encrypt this image.
  6. Continue with the image creation process.

gcloud

gcloud compute \
images create [...] \
    --kms-key projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/KEY

API

To encrypt an imported image, specify the URI to the compressed file, add the imageEncryptionKey property to the image creation request, and specify the key to encrypt the image in the kmsKeyName property:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/global/images

{
"rawDisk": {
 "source": "http://storage.googleapis.com/example-image/example-image.tar.gz"
},
"name": "new-encrypted-image",
"sourceType": "RAW",
"imageEncryptionKey": {
  "kmsKeyName": "projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/IMAGE_KEY"
  }
}

Replace IMAGE_KEY with the name of the key that you want to use to encrypt the image.

Create a persistent disk from a resource encrypted with CMEK

Create a disk from a snapshot encrypted with CMEK

To create a new standalone persistent disk using an encrypted snapshot, do the following:

Console

  1. In the Google Cloud Console, go to the Disks page.

    Go to Disks

  2. Click Create disk and enter the properties for the new disk.
  3. For Source type, select the desired snapshot or image.
  4. Continue with the persistent disk creation process.

gcloud

gcloud compute \
disks create [...] \
    --source-snapshot example-snapshot \
    --kms-key projects/KMS_PROJECT_ID/locations/REGION/keyRings/KEY_RING/cryptoKeys/KEY

To use an image instead of a snapshot, replace --source-snapshot example-snapshot with --image example-image.

API

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/disks

{
"name": "disk-from-encrypted-snapshot",
"sourceSnapshot": "global/snapshots/encrypted-snapshot"
}

Attaching a boot disk encrypted with CMEK to a new VM

Console

  1. In the Google Cloud Console, go to the Create an instance page.

    Go to Create an instance

  2. Specify the VM details, and in the Boot disk section, click Change. Then, do the following:

    1. Click Existing disks.
    2. In the Disk list, select an existing disk to attach to the VM.
    3. Click Select.
  3. Continue with the VM creation process.

gcloud

gcloud compute instances \
create example-instance \
    --disk name=encrypted-disk,boot=yes

API

"disks": [
{
  "deviceName": "encrypted-disk",
  "source": "projects/PROJECT_ID/zones/ZONE/disks/encrypted-disk"
  }
 }
]

Remove your Cloud KMS encryption key from a persistent disk

You can decrypt the contents of an encrypted disk and create a new disk that uses Compute Engine default encryption instead. By default, Compute Engine encrypts all data at rest.

  1. Create a snapshot of the encrypted disk.
  2. Use the new image to create a new persistent disk.

After you create the new persistent disk, it uses Compute Engine default encryption to help protect the disk contents. Any snapshots that you create from that disk must also use default encryption.

Rotate your Cloud KMS encryption key for a persistent disk

Rotate the key that is used to encrypt the disk by creating a new disk that uses a new Cloud KMS key version. Rotating keys is a best practice to comply with standardized security practices. To rotate your keys, do the following:

  1. Rotate your Cloud KMS key.
  2. Create a snapshot of the encrypted disk.
  3. Use the new snapshot to create a new persistent disk with the key rotated in the preceding step.

When you create the new persistent disk, it uses the new key version for encryption. Any snapshots that you create from that disk also use the same key version.

When you rotate a key, data that was encrypted with previous key versions is not automatically re-encrypted. For more information, see Re-encrypting data. Rotating a key does not automatically disable or destroy an existing key version.

Impact of disabling or deleting CMEKs

Disabling or deleting an encryption key has the following effects on the following resources that the key helps to protect:

  • VMs with attached disks cannot boot. If you enabled VM shutdown on key revocation, then VMs with attached disks that the key helps to protect shut down.
  • Disks cannot be attached to VMs, nor can snapshots be created for them.
  • Snapshots cannot be used to create a disk.
  • Images cannot be used to create a disk.

If you disable the key, you can reverse the preceding effects by enabling the key. If you delete the key, you cannot reverse the preceding effects.

Configure VM shutdown on Cloud KMS key revocation

You can configure your VM to shutdown automatically when you revoke the Cloud KMS key that is helping to protect a persistent disk attached to the VM. You can revoke a key by disabling or deleting it. With this setting enabled, the VM shuts down within 3 hours of key revocation.

If you enable the key again, you can restart the VM with the attached disk that the key helps to protect. The VM does not automatically restart after you enable the key.

You can configure a VM to shut down on key revocation when you create the VM using the gcloud tool or the Compute Engine API.

gcloud

Use the gcloud beta compute instances create command to create a VM, and set the field --post-key-revocation-action-type=shutdown.

gcloud beta compute instances create VM_NAME
    --image IMAGE
    --post-key-revocation-action-type=shutdown

API

Use the instances.insert method to create a VM, and set the field "postKeyRevocationActionType": "SHUTDOWN". The following example creates the VM from a public image.

 POST https://compute.googleapis.com/compute/beta/projects/PROJECT_ID/zones/ZONE/instances

{ "machineType": "zones/MACHINE_TYPE_ZONE/machineTypes/MACHINE_TYPE", "name": "VM_NAME", "disks": [ { "initializeParams": { "sourceImage": "projects/IMAGE_PROJECT/global/images/IMAGE" }, "boot": true } ], "postKeyRevocationActionType": "SHUTDOWN" }

Alternatively, you can configure an instance template to create VMs that shut down on key revocation by using the gcloud tool or the Compute Engine API.

gcloud

Create an instance template by using the instance-templates create command, and set the field --post-key-revocation-action-type=shutdown.

gcloud beta compute instance-templates create INSTANCE_TEMPLATE_NAME \
    --post-key-revocation-action-type=shutdown

API

Create an instance template by using the instanceTemplates().insert method. In the instance template API, you must explicitly define all of the required configuration fields. If you want VMs created from this template to shut down on key revocation, specify "postKeyRevocationActionType": "SHUTDOWN". For example, an instance template with the minimal required fields that will create VMs that shut down on key revocation looks like the following:

  {
  "name": "example-template",
  "properties": {
    "machineType": "e2-standard-4",
    "networkInterfaces": [
      {
        "network": "global/networks/default",
        "accessConfigs":
        [
          {
            "name": "external-IP",
            "type": "ONE_TO_ONE_NAT"
          }
        ]
      }
    ],
    "disks":
    [
      {
        "type": "PERSISTENT",
        "boot": true,
        "mode": "READ_WRITE",
        "initializeParams":
        {
          "sourceImage": "projects/debian-cloud/global/images/family/debian-9"
        }
      }
    ],
    "postKeyRevocationActionType": "SHUTDOWN"
    }
  }
  

After you create a VM that is configured to shut down on Cloud KMS revocation, create and attach a persistent disk encrypted with a Cloud KMS key.