# Python envelope encryption example

This example shows how to encrypt data with Tink using
[Envelope Encryption](https://cloud.google.com/kms/docs/envelope-encryption).

It shows how you can use Tink to encrypt data with a newly generated *data
encryption key* (DEK) which is wrapped with a KMS key. The data will be
encrypted with AES256 GCM using the DEK and the DEK will be encrypted with the
KMS key and stored alongside the ciphertext.

The CLI takes 5 arguments:

*   mode: "encrypt" or "decrypt" to indicate if you want to encrypt or decrypt.
*   kek-uri: The URI for the key to be used for envelope encryption.
*   gcp-credential-file: Name of the file with the GCP credentials in JSON
    format.
*   input-file: Read the input from this file.
*   output-file: Write the result to this file.

## Build and Run

### Prequisite

This envelope encryption example uses a Cloud KMS key as a key-encryption key
(KEK). In order to run it, you need to:

*   Create a symmetric key on Cloud KMs. Copy the key URI which is in this
    format:
    `projects/<my-project>/locations/global/keyRings/<my-key-ring>/cryptoKeys/<my-key>`.

*   Create a service account that is allowed to encrypt and decrypt with the
    above key and download a JSON credentials file.

### Bazel

```shell
$ git clone https://github.com/google/tink
$ cd tink/python/examples
$ bazel build ...
```

You can then encrypt a file:

```shell
$ echo "some data" > testdata.txt

# Replace `<my-key-uri>` in `gcp-kms://<my-key-uri>` with your key URI, and
# my-service-account.json with your service account's credential JSON file.

$ ./bazel-bin/envelope/envelope --mode encrypt \
    --gcp_credential_path my-service-account.json \
    --kek_uri gcp-kms://<my-key-uri> \
    --input_path testdata.txt --output_path testdata.txt.encrypted
```

Or decrypt the file with:

```shell
$ ./bazel-bin/envelope/envelope --mode decrypt \
     --gcp_credential_path my-service-account.json \
     --kek_uri gcp-kms://<my-key-uri> \
     --input_path testdata.txt.encrypted --output_path testdata.txt
```

### Pip package

```shell
$ git clone https://github.com/google/tink
$ cd tink/python
$ pip3 install .
```

You can then encrypt the file:

```shell
$ echo "some data" > testdata.txt
$ python3 envelope.py --mode encrypt \
    --gcp_credential_path my-service-account.json \
    --kek_uri gcp-kms://<my-key-uri> \
    --input_path testdata.txt --output_path testdata.txt.encrypted
```