SecretKeeper implementation for Goole Cloud KMS

CloudKMS SecretKeeper uris are of the form cloudkms://PROJECT/LOCATION/KEYRING/KEY, where

• PROJECT is the google cloud kms project
• LOCATION is the cloud location; use 'global' for all data centers/zones
• KEYRING - your keyring name
• KEY - your key name

You must set the environment variable GOOGLE_APPLICATION_CREDENTIALS to the path to a credentials json file (e.g., for a service account).

Prerequisites

• A google cloud account, with the Cloud KMS API enabled for your project
• An authorized user or service account, with the following role enabled:
  • Cloud KMS CryptoKey Encrypter/Decrypter
• The environment variable GOOGLE_APPLICATION_CREDENTIALS is set to the path of the json credentials file for the authorized account.
• Google Cloud SDK tools installed (gcloud is needed for the exapmles below)

Create Keyring and Key, if necessary

You may use an existing keyring and key, or create one. You will need to know the name of availability zone, or use global for for all zones.

• To create the keyring my_keyring,

gcloud kms keyrings create "my_keyring" --location global

• To create a key my_key on the my_keyring key,

gcloud kms keys create my_key --keyring my_keyring --location global \
    --purpose encryption-decryption

Using this keeper

The format of the keeper uri is cloudkms:/PROJECT/LOCATION/KEYRING/KEY, so, the uri for our new keyring and key are cloudkms:/PROJECT/global/my_keyring/key,

You can test it out with the examples/encrypt-rs command-line program. To encrypt FILE to FILE.ENC, use:

  encrypt enc -o FILE.ENC -k cloudkms:/PROJECT/global/my_keyring/my_key FILE

To decrypt, use

  encrypt dec -o FILE.DUP -k cloudkms:/PROJECT/global/my_keyring/my_key FILE.ENC

With default parameters, this will encrypt the file using the LZ4XChaCha20-Poly1305 compressing cipher, using a newly-generated 256-bit key, encrypt that key with my_keyring/my_key on Google CloudKMS, and store the encrypted key in the header of FILE.ENC.