python-fido2/fido2/server.py

# Copyright (c) 2018 Yubico AB
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#   without modification, are permitted provided that the following
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#       notice, this list of conditions and the following disclaimer.
#    2. Redistributions in binary form must reproduce the above
#       copyright notice, this list of conditions and the following
#       disclaimer in the documentation and/or other materials provided
#       with the distribution.
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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from __future__ import absolute_import, unicode_literals

from .rpid import verify_rp_id
from .cose import ES256
from .client import WEBAUTHN_TYPE
from .utils import sha256

import os
import six
from enum import Enum, unique
from cryptography.hazmat.primitives import constant_time


def _verify_origin_for_rp(rp_id):
    return lambda o: verify_rp_id(rp_id, o)


@unique
class ATTESTATION(six.text_type, Enum):
    NONE = 'none'
    INDIRECT = 'indirect'
    DIRECT = 'direct'


@unique
class USER_VERIFICATION(six.text_type, Enum):
    DISCOURAGED = 'discouraged'
    PREFERRED = 'preferred'
    REQUIRED = 'required'


class Fido2Server(object):
    def __init__(
            self,
            rp,
            attestation=ATTESTATION.NONE,
            verify_origin=None,
            resident_key=False,
            user_verification=USER_VERIFICATION.PREFERRED
    ):
        self.rp = rp
        self._verify = verify_origin or _verify_origin_for_rp(rp['id'])
        self.timeout = 30
        self.attestation = ATTESTATION(attestation)
        self.allowed_algorithms = [ES256.ALGORITHM]
        self.user_verification = USER_VERIFICATION(user_verification)
        self.resident_key = resident_key

    def register_begin(self, user, credentials=None):
        if not self.allowed_algorithms:
            raise ValueError('Server has no allowed algorithms.')

        challenge = os.urandom(32)
        return {
            'publicKey': {
                'rp': self.rp,
                'user': user,
                'challenge': challenge,
                'pubKeyCredParams': [
                    {
                        'type': 'public-key',
                        'alg': alg
                    } for alg in self.allowed_algorithms
                ],
                'excludeCredentials': [
                    {
                        'type': 'public-key',
                        'id': cred.credential_id
                    } for cred in credentials or []
                ],
                'timeout': int(self.timeout * 1000),
                'attestation': self.attestation,
                'authenticatorSelection': {
                    'requireResidentKey': self.resident_key,
                    'userVerification': self.user_verification
                }
            }
        }

    def register_complete(self, challenge, client_data, attestation_object):
        if client_data.get('type') != WEBAUTHN_TYPE.MAKE_CREDENTIAL:
            raise ValueError('Incorrect type in ClientData.')
        if not self._verify(client_data.get('origin')):
            raise ValueError('Invalid origin in ClientData.')
        if not constant_time.bytes_eq(challenge, client_data.challenge):
            raise ValueError('Wrong challenge in response.')
        if not constant_time.bytes_eq(sha256(self.rp['id'].encode()),
                                      attestation_object.auth_data.rp_id_hash):
            raise ValueError('Wrong RP ID hash in response.')
        if attestation_object.fmt == ATTESTATION.NONE \
                and self.attestation != ATTESTATION.NONE:
            raise ValueError('Attestation required, but not provided.')
        attestation_object.verify(client_data.hash)

        if self.user_verification is USER_VERIFICATION.REQUIRED and \
           not attestation_object.auth_data.is_user_verified():
            raise ValueError(
                'User verification required, but User verified flag not set.')

        return attestation_object.auth_data

    def authenticate_begin(self, credentials):
        challenge = os.urandom(32)
        return {
            'publicKey': {
                'rpId': self.rp['id'],
                'challenge': challenge,
                'allowCredentials': [
                    {
                        'type': 'public-key',
                        'id': cred.credential_id
                    } for cred in credentials
                ],
                'timeout': int(self.timeout * 1000),
                'userVerification': self.user_verification
            }
        }

    def authenticate_complete(self, credentials, credential_id, challenge,
                              client_data, auth_data, signature):
        if client_data.get('type') != WEBAUTHN_TYPE.GET_ASSERTION:
            raise ValueError('Incorrect type in ClientData.')
        if not self._verify(client_data.get('origin')):
            raise ValueError('Invalid origin in ClientData.')
        if challenge != client_data.challenge:
            raise ValueError('Wrong challenge in response.')
        if not constant_time.bytes_eq(sha256(self.rp['id'].encode()),
                                      auth_data.rp_id_hash):
            raise ValueError('Wrong RP ID hash in response.')

        if self.user_verification is USER_VERIFICATION.REQUIRED and \
           not auth_data.is_user_verified():
            raise ValueError(
                'User verification required, but user verified flag not set.')

        for cred in credentials:
            if cred.credential_id == credential_id:
                cred.public_key.verify(auth_data + client_data.hash, signature)
                return cred
        raise ValueError('Unknown credential ID.')