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# Copyright 2017 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""ECDSA (ES256) verifier and signer that use the ``cryptography`` library.
"""
from cryptography import utils
import cryptography.exceptions
from cryptography.hazmat import backends
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
from cryptography.hazmat.primitives.asymmetric.utils import encode_dss_signature
import cryptography.x509
from google.auth import _helpers
from google.auth.crypt import base
_CERTIFICATE_MARKER = b"-----BEGIN CERTIFICATE-----"
_BACKEND = backends.default_backend()
_PADDING = padding.PKCS1v15()
class ES256Verifier(base.Verifier):
"""Verifies ECDSA cryptographic signatures using public keys.
Args:
public_key (
cryptography.hazmat.primitives.asymmetric.ec.ECDSAPublicKey):
The public key used to verify signatures.
"""
def __init__(self, public_key):
self._pubkey = public_key
@_helpers.copy_docstring(base.Verifier)
def verify(self, message, signature):
# First convert (r||s) raw signature to ASN1 encoded signature.
sig_bytes = _helpers.to_bytes(signature)
if len(sig_bytes) != 64:
return False
r = utils.int_from_bytes(sig_bytes[:32], byteorder="big")
s = utils.int_from_bytes(sig_bytes[32:], byteorder="big")
asn1_sig = encode_dss_signature(r, s)
message = _helpers.to_bytes(message)
try:
self._pubkey.verify(asn1_sig, message, ec.ECDSA(hashes.SHA256()))
return True
except (ValueError, cryptography.exceptions.InvalidSignature):
return False
@classmethod
def from_string(cls, public_key):
"""Construct an Verifier instance from a public key or public
certificate string.
Args:
public_key (Union[str, bytes]): The public key in PEM format or the
x509 public key certificate.
Returns:
Verifier: The constructed verifier.
Raises:
ValueError: If the public key can't be parsed.
"""
public_key_data = _helpers.to_bytes(public_key)
if _CERTIFICATE_MARKER in public_key_data:
cert = cryptography.x509.load_pem_x509_certificate(
public_key_data, _BACKEND
)
pubkey = cert.public_key()
else:
pubkey = serialization.load_pem_public_key(public_key_data, _BACKEND)
return cls(pubkey)
class ES256Signer(base.Signer, base.FromServiceAccountMixin):
"""Signs messages with an ECDSA private key.
Args:
private_key (
cryptography.hazmat.primitives.asymmetric.ec.ECDSAPrivateKey):
The private key to sign with.
key_id (str): Optional key ID used to identify this private key. This
can be useful to associate the private key with its associated
public key or certificate.
"""
def __init__(self, private_key, key_id=None):
self._key = private_key
self._key_id = key_id
@property
@_helpers.copy_docstring(base.Signer)
def key_id(self):
return self._key_id
@_helpers.copy_docstring(base.Signer)
def sign(self, message):
message = _helpers.to_bytes(message)
asn1_signature = self._key.sign(message, ec.ECDSA(hashes.SHA256()))
# Convert ASN1 encoded signature to (r||s) raw signature.
(r, s) = decode_dss_signature(asn1_signature)
return utils.int_to_bytes(r, 32) + utils.int_to_bytes(s, 32)
@classmethod
def from_string(cls, key, key_id=None):
"""Construct a RSASigner from a private key in PEM format.
Args:
key (Union[bytes, str]): Private key in PEM format.
key_id (str): An optional key id used to identify the private key.
Returns:
google.auth.crypt._cryptography_rsa.RSASigner: The
constructed signer.
Raises:
ValueError: If ``key`` is not ``bytes`` or ``str`` (unicode).
UnicodeDecodeError: If ``key`` is ``bytes`` but cannot be decoded
into a UTF-8 ``str``.
ValueError: If ``cryptography`` "Could not deserialize key data."
"""
key = _helpers.to_bytes(key)
private_key = serialization.load_pem_private_key(
key, password=None, backend=_BACKEND
)
return cls(private_key, key_id=key_id)
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