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CTAP (client-to-authenticator-protocol) device backed by python's keyring library

Project description

PyPi version Python version Code style: Black Read the docs CI workflow

This library provides an implementation of a virtual CTAP2 (client-to-authenticator-protocol) device, which uses the keyring library as its backend.

One may use this implementation as a reference for CTAP2-compatible devices, or to use ones host machine as an authenticator, rather than using an external one.

A common use-case would be to use this library as an authenticator for a webauthn flow, storing keys and retrieving assertions on a machine’s configured keyring.

Supported features are:
  • The make-credential, get-assertion, get-next-assertion and get-info CTAP2 flows
  • The management of keys using the following COSE algorithms: RS1, RS256, PS256, EC256, EdDSA
  • The use of any available keyring as a backend for the created key-pairs (e.g. WinCred, Keychain, …)
  • User presence & verification on OSX and Windows, via Touch-ID and Windows-Hello
  • Storing keys in a secure manner, with no PII (personal-identifying-information) attached to them

Installation

Run the following (on a darwin machine):

$ pip install ctap-keyring-device

Using This Library

Make Credential Flow

from fido2.webauthn import PublicKeyCredentialCreationOptions, PublicKeyCredentialType, PublicKeyCredentialParameters
from ctap_keyring_device.ctap_keyring_device import CtapKeyringDevice
from fido2.client import Fido2Client
from fido2 import cose
import base64

device = CtapKeyringDevice.list_devices()[0]
origin = 'https://rp.pasten.com'
client = Fido2Client(device, origin)

rp = {'id': 'pasten.com', 'name': origin[8:], 'icon': '...'}
user = {'id': 'danny@pasten.io', 'name': 'Danny Shemesh', 'icon': '...', 'displayName': 'Danny Pastanny'}
challenge = base64.b64encode(b'my-challenge')
timeout_ms = 30_000

pub_key_cred_params = [PublicKeyCredentialParameters(PublicKeyCredentialType.PUBLIC_KEY, cose.ES256.ALGORITHM)]
options = PublicKeyCredentialCreationOptions(rp, user, challenge, pub_key_cred_params, timeout=timeout_ms)

attestation, client_data = client.make_credential(options)

Get Assertion Flow

from fido2.webauthn import PublicKeyCredentialRequestOptions, PublicKeyCredentialType, \
    PublicKeyCredentialParameters, PublicKeyCredentialDescriptor, UserVerificationRequirement
from ctap_keyring_device.ctap_keyring_device import CtapKeyringDevice
from fido2.client import Fido2Client
from fido2 import cose
import base64

device = CtapKeyringDevice.list_devices()[0]
origin = 'https://rp.pasten.com'
client = Fido2Client(device, origin)

challenge = base64.b64encode(b'my-challenge')
rp = {'id': 'pasten.com', 'name': origin[8:], 'icon': '...'}
credential_id = b'.......'
allow_list = [
    PublicKeyCredentialDescriptor(PublicKeyCredentialType.PUBLIC_KEY, credential_id)
]
timeout_ms = 30_000

pub_key_cred_params = [PublicKeyCredentialParameters(PublicKeyCredentialType.PUBLIC_KEY, cose.ES256.ALGORITHM)]
options = PublicKeyCredentialRequestOptions(challenge=challenge, rp_id=rp['id'],
                                            allow_credentials=allow_list, timeout=timeout_ms,
                                            user_verification=UserVerificationRequirement.PREFERRED)
assertions, client_data = client.get_assertion(options)

See examples in ctap-keyring-device/tests.


CTAP Flow Diagrams

Make Credential Flow

Make Credential Flow

Get Assertion Flow

Get Assertion Flow

Security Considerations

Using this library will help one utilize their machine’s keyring as a CTAP2-compliant FIDO authenticator.

Credentials are stores on the configured keyring, which defaults to a sensible implementation, per the platform the code is running on (e.g. keychain on OSX, WinCred on Windows, …)

The make-credentials flow will create a key-pair for signing, using the requested COSE algorithm.

Private keys are encrypted with a random UUID4 as the passphrase, using hazmat’s BestAvailableEncryption.

Credential IDs comprise of <UUID5-of-user-id>_<key-passphrase>, and are sent back to the requesting client; it is assumed that the credential ID is kept in a remote machine, and is always provided in the allow-list of a ctap get-assertion request.

The above allows us to generate and store our keys in a manner that renders key exposure as less risky, due to the key being encrypted; and not storing the user-id directly, making it harder to use the key, even if decrypted.

On top of the mentioned safeguards, one may request the UV (user-verification) option, in order to trigger a 2nd factor before returning an assertion; Touch-ID / Password prompt is used on OSX, and Windows-Hello on Windows.


Making Releases

A CI/CD pipeline is setup on github - once a PR is merged to master, a pre-release will be automatically deployed to github; When a release is tagged, it will be automatically deployed to pypi.


Running Tests

To run the tests locally, install and invoke tox.

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