django-dreiattest

dreiattest leverages pyattest and integrates it into django. It handles routing, different config options and persistence of tokens and public keys. To use dreiAttest you need to use the corresponing libraries for iOS and Android / Kotlin Multiplatform.

Installation

dreiAttest is available on PyPI and can be installed via $ python -m pip install dreiattest-django.

After the installation make sure to add dreiattest to your INSTALLED_APPS and trigger all migrations with python manage.py migrate dreiattest. Also, you need to register the default endpoints in your urls.py

urlpatterns = [
    path('admin/', admin.site.urls),
    path('', include('dreiattest.urls')),
    ...
]

Configuration

These are all the possible config values and what they do.

• DREIATTEST_BASE_URL: Our different endpoints like /key and /nonce will be below this slug
• DREIATTEST_BYPASS_SECRET: The shared secret to bypass the verification process. Helpful for debugging
• DREIATTEST_APPLE_APPIDS: The list of apple app ids (consisting of the team id + bundle id)
• DREIATTEST_PLAY_INTEGRITY_CONFIGS: A json-object containing one or more configuration objects. Apps trying to connect to your server need to match one of these configurations. If there are multiple configurations for a given package identifier, they are tested in order. It is, therefore, recommended to list the configuration you expect to work for most clients first. The following configuration options are available:
  • apk_name: The package identifier of your Android app
  • decryption_key: A Base64 encoded AES key secret as described here. It can be obtained by switching to self-managed keys as described here.
  • verification_key: A Base64 encoded public key as described here. It can be obtained by switching to self-managed keys as described here.
  • (optional) certificate_digest: SHA256 hex of the Google APK Certificate
  • (optional) allow_non_play_installs: Allow apps that were not installed via the Play Store to connect to your server. These will be verified via the signing certificate instead. (certificate_digest must be set)
  • (optional) required_device_verdict: The minimum device integrty verdict that must be present.
• DREIATTEST_PRODUCTION: Indicating if we're in a production environment or not. Some extra verifications are made if this is true. Those are described in the pyttest readme.
• DREIATTEST_PLUGINS: List of classes implementing BasePlugin - gives you the option to handle extra verification
• DREIATTEST_BYPASS_SECRET: DANGERZONE If this is set and DREIATTEST_BYPASS_HEADER is sent by the client, the verification is skipped.

You can find the default value (if any) for each of them in the settings.py

Sample Configuration

In your base.py this may look like this:

DREIATTEST_APPLE_APPIDS = env.list('DREIATTEST_APPLE_APPIDS', default=['0000000000.ch.dreipol.ios1', '0000000000.ch.dreipol.ios2'])
DREIATTEST_PRODUCTION = env('DREIATTEST_PRODUCTION', default=True)
DREIATTEST_BYPASS_SECRET = env('DREIATTEST_BYPASS_SECRET', default=None)
DREIATTEST_PLAY_INTEGRITY_CONFIGS = [
    {
        "apk_name": "ch.dreipol.android1",
        "decryption_key": env('DREIATTEST_GOOGLE_DECRYPTION_KEY1', default=None),
        "verification_key": env('DREIATTEST_GOOGLE_VERIFICATION_KEY1', default=None),
        "required_device_verdict": "MEETS_STRONG_INTEGRITY"
    },
    {
        "apk_name": "ch.dreipol.android2",
        "decryption_key": env('DREIATTEST_GOOGLE_DECRYPTION_KEY2', default=None),
        "verification_key": env('DREIATTEST_GOOGLE_VERIFICATION_KEY2', default=None)
    },
    {
        "apk_name": "ch.dreipol.android2",
        "decryption_key": env('DREIATTEST_GOOGLE_DECRYPTION_KEY2', default=None),
        "verification_key": env('DREIATTEST_GOOGLE_VERIFICATION_KEY2', default=None),
        "allow_non_play_installs": True,
        "certificate_digest": env('DREIATTEST_GOOGLE_APK_CERTIFICATE_DIGEST', default=None)
    }
]

Usage

All that's left is to add the signature_required view decorator.

from dreiattest.decorators import signature_required

@signature_required()
def demo(request: WSGIRequest):
    return JsonResponse({'foo': 'bar'})

Error Handling

The main two exceptions that should be handled by you are PyAttestException and DreiAttestException. dreiattest ships with the HandleDreiattestExceptionsMiddleware you could use if you don't want to handle those errors by yourself. The middleware only catches those two exception classes and returns a JsonResponse with status code 400.

MIDDLEWARE = [
    ...
    'dreiattest.middlewares.HandleDreiattestExceptionsMiddleware',
]

Typical Flow

1. CLIENT (could be android or google) makes a request to dreiattest/nonce with a device session identifier to obtain a server nonce. The session id as well as the nonce are persisted on the server.
2. CLIENT sends an attestation to dreiattest/key. This request again holds the device session identifier as well as the nonce from step 1. The nonce will be marked as "used" and used to verify the attestation. The public key from the client is then assigned to the device session and also persisted in the database.
3. CLIENT sends a request to any view decorated with @signature_required. The request holds an assertion which will be verified before the actual django view is executed.

Common issues

If you are using Play Integrity and your app is distributed via the Play Store you do not need to provide the DREIATTEST_GOOGLE_APK_CERTIFICATE_DIGEST as the signing key is already checked by the Play Store. If you do provide a value for DREIATTEST_GOOGLE_APK_CERTIFICATE_DIGEST both the key and the verdict from the Play Integrity API are checked. Note in that case that the Play Store re-signs your app with a different key before distributing it. You can find the relevant digest in the play console under Setup > App signing.

Debugging Advice

• Setting DREIATTEST_PRODUCTION = False

  • Android: Only the package identifier is checked. Note that this does not provide any security guarantees since anyone can build an app with a specific package identifier.
  • iOS: Allows dev and production builds to connect to your server. Since iOS requires you to register an App Id to use App Attest this provides some weakened security guarantees. The checks are performed normally but a different environment is used for Apple's attestation api. This should be sufficient to validate your configuration.
  • Additionally it is possible to connect to the server using the DREIATTEST_BYPASS_SECRET.

• Setting allow_non_play_installs = True

  • Allows Android apps to connect even if they were not distributed via the Play Store (e.g. dev builds). All the checks are run but instead of letting the Play Store verify your build and signing key the DREIATTEST_GOOGLE_APK_CERTIFICATE_DIGEST is checked. This can be a useful intermediate step to verify your configuration before publishing on the Play Store. Note that once you publish your app on the Play Store you shuld set the value back to DREIATTEST_GOOGLE_ALLOW_NON_PLAY_INSTALLS = False and remove or adjust your DREIATTEST_GOOGLE_APK_CERTIFICATE_DIGEST (see Common issues above).

Before publishing your app on the App Store / Play Store you should validate your setup using a Test Flight / Testing Channel Build. These behave the same as production builds.

Publishing / Contributing

• Create a branch from master for possible pull requests
• To publish a new version to pypi:
  • Update the version in __version__.py
  • Trigger $ pipenv run upload - This will automatically create and push the correct tag in git and upload that version to pypi