Description

Google Cloud Key Management Service stores cryptographic keys in a hierarchical structure designed for useful and elegant access control management. The format for the rotation schedule depends on the client library that is used. For the gcloud CLI, the flag --next-rotation-time must be in ISO or RFC3339 format; the flag --rotation-period must be in the format INTEGER[UNIT], where units can be one of: seconds (s), minutes (m), hours (h), or days (d). For example, 30d for a rotation period of 30 days.

Rationale

Set a key rotation period and starting time. A key can be created with a specified rotation period, which is the time between when new key versions are generated automatically. A key can also be created with a specified next rotation time.

A key is a named object that represents a cryptographic key and is used for a specific purpose. The key material (the actual bits used for encryption) can change over time as new key versions are created. A key is used to protect a corpus of data. A collection of files could be encrypted with the same key, and people with decrypt permissions on that key would be able to decrypt those files. Therefore, it’s necessary to make sure the rotation period is set to a specific time.

Impact

After a successful key rotation, the older key version is required to decrypt the data encrypted by the previous key version.

Remediation

From the console

1. See your cryptographic keys by visiting: https://console.cloud.google.com/security/kms.
2. Click on the specific key ring.
3. From the list of keys, locate the key you wish to edit. Click on the three vertical dots under the Actions column.
4. Click on Edit rotation period.
5. In the pop-up window, select a new rotation period. Choose value less than 90 days. Then, choose the date from which the rotation period begins.

From the command line

1. Update and schedule rotation by ROTATION_PERIOD and NEXT_ROTATION_TIME for each key: For example, you can use the iam.json file shown below as follows:

    gcloud kms keys update new --keyring=KEY_RING --location=LOCATION --next- rotation-time=NEXT_ROTATION_TIME --rotation-period=ROTATION_PERIOD
   

Default value

By default, KMS encryption keys are rotated every 90 days.

References

1. https://cloud.google.com/kms/docs/key-rotation#frequency_of_key_rotation
2. https://cloud.google.com/kms/docs/re-encrypt-data

Additional Information

A user-managed key cannot be created on GCP-Managed Service Accounts.