# Copyright (c) 2020 Yubico AB
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# without modification, are permitted provided that the following
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from __future__ import annotations
from .base import (
Attestation,
AttestationType,
AttestationResult,
InvalidData,
catch_builtins,
)
from ..utils import sha256
from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.constant_time import bytes_eq
OID_APPLE = x509.ObjectIdentifier("1.2.840.113635.100.8.2")
[docs]
class AppleAttestation(Attestation):
FORMAT = "apple"
[docs]
@catch_builtins
def verify(self, statement, auth_data, client_data_hash):
x5c = statement["x5c"]
expected_nonce = sha256(auth_data + client_data_hash)
cert = x509.load_der_x509_certificate(x5c[0], default_backend())
ext = cert.extensions.get_extension_for_oid(OID_APPLE)
ext_nonce = ext.value.value[6:] # Sequence of single element of octet string
if not bytes_eq(expected_nonce, ext_nonce):
raise InvalidData("Nonce does not match!")
return AttestationResult(AttestationType.ANON_CA, x5c)