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# Copyright 2016 Google LLC
#
# 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.
"""Cryptography helpers for verifying and signing messages.
The simplest way to verify signatures is using :func:`verify_signature`::
cert = open('certs.pem').read()
valid = crypt.verify_signature(message, signature, cert)
If you're going to verify many messages with the same certificate, you can use
:class:`RSAVerifier`::
cert = open('certs.pem').read()
verifier = crypt.RSAVerifier.from_string(cert)
valid = verifier.verify(message, signature)
To sign messages use :class:`RSASigner` with a private key::
private_key = open('private_key.pem').read()
signer = crypt.RSASigner.from_string(private_key)
signature = signer.sign(message)
The code above also works for :class:`ES256Signer` and :class:`ES256Verifier`.
Note that these two classes are only available if your `cryptography` dependency
version is at least 1.4.0.
"""
import six
from google.auth.crypt import base
from google.auth.crypt import rsa
try:
from google.auth.crypt import es256
except ImportError: # pragma: NO COVER
es256 = None
if es256 is not None: # pragma: NO COVER
__all__ = [
"ES256Signer",
"ES256Verifier",
"RSASigner",
"RSAVerifier",
"Signer",
"Verifier",
]
else: # pragma: NO COVER
__all__ = ["RSASigner", "RSAVerifier", "Signer", "Verifier"]
# Aliases to maintain the v1.0.0 interface, as the crypt module was split
# into submodules.
Signer = base.Signer
Verifier = base.Verifier
RSASigner = rsa.RSASigner
RSAVerifier = rsa.RSAVerifier
if es256 is not None: # pragma: NO COVER
ES256Signer = es256.ES256Signer
ES256Verifier = es256.ES256Verifier
def verify_signature(message, signature, certs, verifier_cls=rsa.RSAVerifier):
"""Verify an RSA or ECDSA cryptographic signature.
Checks that the provided ``signature`` was generated from ``bytes`` using
the private key associated with the ``cert``.
Args:
message (Union[str, bytes]): The plaintext message.
signature (Union[str, bytes]): The cryptographic signature to check.
certs (Union[Sequence, str, bytes]): The certificate or certificates
to use to check the signature.
verifier_cls (Optional[~google.auth.crypt.base.Signer]): Which verifier
class to use for verification. This can be used to select different
algorithms, such as RSA or ECDSA. Default value is :class:`RSAVerifier`.
Returns:
bool: True if the signature is valid, otherwise False.
"""
if isinstance(certs, (six.text_type, six.binary_type)):
certs = [certs]
for cert in certs:
verifier = verifier_cls.from_string(cert)
if verifier.verify(message, signature):
return True
return False
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