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_pure_python_crypt.py
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_pure_python_crypt.py
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# Copyright 2016 Google Inc. All rights reserved.
#
# 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.
"""Pure Python crypto-related routines for oauth2client.
Uses the ``rsa``, ``pyasn1`` and ``pyasn1_modules`` packages
to parse PEM files storing PKCS#1 or PKCS#8 keys as well as
certificates.
"""
from pyasn1.codec.der import decoder
from pyasn1_modules import pem
from pyasn1_modules.rfc2459 import Certificate
from pyasn1_modules.rfc5208 import PrivateKeyInfo
import rsa
import six
from oauth2client import _helpers
_PKCS12_ERROR = r"""\
PKCS12 format is not supported by the RSA library.
Either install PyOpenSSL, or please convert .p12 format
to .pem format:
$ cat key.p12 | \
> openssl pkcs12 -nodes -nocerts -passin pass:notasecret | \
> openssl rsa > key.pem
"""
_POW2 = (128, 64, 32, 16, 8, 4, 2, 1)
_PKCS1_MARKER = ('-----BEGIN RSA PRIVATE KEY-----',
'-----END RSA PRIVATE KEY-----')
_PKCS8_MARKER = ('-----BEGIN PRIVATE KEY-----',
'-----END PRIVATE KEY-----')
_PKCS8_SPEC = PrivateKeyInfo()
def _bit_list_to_bytes(bit_list):
"""Converts an iterable of 1's and 0's to bytes.
Combines the list 8 at a time, treating each group of 8 bits
as a single byte.
"""
num_bits = len(bit_list)
byte_vals = bytearray()
for start in six.moves.xrange(0, num_bits, 8):
curr_bits = bit_list[start:start + 8]
char_val = sum(val * digit
for val, digit in zip(_POW2, curr_bits))
byte_vals.append(char_val)
return bytes(byte_vals)
class RsaVerifier(object):
"""Verifies the signature on a message.
Args:
pubkey: rsa.key.PublicKey (or equiv), The public key to verify with.
"""
def __init__(self, pubkey):
self._pubkey = pubkey
def verify(self, message, signature):
"""Verifies a message against a signature.
Args:
message: string or bytes, The message to verify. If string, will be
encoded to bytes as utf-8.
signature: string or bytes, The signature on the message. If
string, will be encoded to bytes as utf-8.
Returns:
True if message was signed by the private key associated with the
public key that this object was constructed with.
"""
message = _helpers._to_bytes(message, encoding='utf-8')
try:
return rsa.pkcs1.verify(message, signature, self._pubkey)
except (ValueError, rsa.pkcs1.VerificationError):
return False
@classmethod
def from_string(cls, key_pem, is_x509_cert):
"""Construct an RsaVerifier instance from a string.
Args:
key_pem: string, public key in PEM format.
is_x509_cert: bool, True if key_pem is an X509 cert, otherwise it
is expected to be an RSA key in PEM format.
Returns:
RsaVerifier instance.
Raises:
ValueError: if the key_pem can't be parsed. In either case, error
will begin with 'No PEM start marker'. If
``is_x509_cert`` is True, will fail to find the
"-----BEGIN CERTIFICATE-----" error, otherwise fails
to find "-----BEGIN RSA PUBLIC KEY-----".
"""
key_pem = _helpers._to_bytes(key_pem)
if is_x509_cert:
der = rsa.pem.load_pem(key_pem, 'CERTIFICATE')
asn1_cert, remaining = decoder.decode(der, asn1Spec=Certificate())
if remaining != b'':
raise ValueError('Unused bytes', remaining)
cert_info = asn1_cert['tbsCertificate']['subjectPublicKeyInfo']
key_bytes = _bit_list_to_bytes(cert_info['subjectPublicKey'])
pubkey = rsa.PublicKey.load_pkcs1(key_bytes, 'DER')
else:
pubkey = rsa.PublicKey.load_pkcs1(key_pem, 'PEM')
return cls(pubkey)
class RsaSigner(object):
"""Signs messages with a private key.
Args:
pkey: rsa.key.PrivateKey (or equiv), The private key to sign with.
"""
def __init__(self, pkey):
self._key = pkey
def sign(self, message):
"""Signs a message.
Args:
message: bytes, Message to be signed.
Returns:
string, The signature of the message for the given key.
"""
message = _helpers._to_bytes(message, encoding='utf-8')
return rsa.pkcs1.sign(message, self._key, 'SHA-256')
@classmethod
def from_string(cls, key, password='notasecret'):
"""Construct an RsaSigner instance from a string.
Args:
key: string, private key in PEM format.
password: string, password for private key file. Unused for PEM
files.
Returns:
RsaSigner instance.
Raises:
ValueError if the key cannot be parsed as PKCS#1 or PKCS#8 in
PEM format.
"""
key = _helpers._from_bytes(key) # pem expects str in Py3
marker_id, key_bytes = pem.readPemBlocksFromFile(
six.StringIO(key), _PKCS1_MARKER, _PKCS8_MARKER)
if marker_id == 0:
pkey = rsa.key.PrivateKey.load_pkcs1(key_bytes,
format='DER')
elif marker_id == 1:
key_info, remaining = decoder.decode(
key_bytes, asn1Spec=_PKCS8_SPEC)
if remaining != b'':
raise ValueError('Unused bytes', remaining)
pkey_info = key_info.getComponentByName('privateKey')
pkey = rsa.key.PrivateKey.load_pkcs1(pkey_info.asOctets(),
format='DER')
else:
raise ValueError('No key could be detected.')
return cls(pkey)