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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.
"""Pure-Python RSA cryptography implementation.
Uses the ``rsa``, ``pyasn1`` and ``pyasn1_modules`` packages
to parse PEM files storing PKCS#1 or PKCS#8 keys as well as
certificates. There is no support for p12 files.
"""
from __future__ import absolute_import
import io
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
from google.auth import _helpers
from google.auth.crypt import base
_POW2 = (128, 64, 32, 16, 8, 4, 2, 1)
_CERTIFICATE_MARKER = b"-----BEGIN CERTIFICATE-----"
_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 1s and 0s to bytes.
Combines the list 8 at a time, treating each group of 8 bits
as a single byte.
Args:
bit_list (Sequence): Sequence of 1s and 0s.
Returns:
bytes: The decoded bytes.
"""
num_bits = len(bit_list)
byte_vals = bytearray()
for start in range(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(base.Verifier):
"""Verifies RSA cryptographic signatures using public keys.
Args:
public_key (rsa.key.PublicKey): 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):
message = _helpers.to_bytes(message)
try:
return rsa.pkcs1.verify(message, signature, self._pubkey)
except (ValueError, rsa.pkcs1.VerificationError):
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:
google.auth.crypt._python_rsa.RSAVerifier: The constructed verifier.
Raises:
ValueError: If the public_key can't be parsed.
"""
public_key = _helpers.to_bytes(public_key)
is_x509_cert = _CERTIFICATE_MARKER in public_key
# If this is a certificate, extract the public key info.
if is_x509_cert:
der = rsa.pem.load_pem(public_key, "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(public_key, "PEM")
return cls(pubkey)
class RSASigner(base.Signer, base.FromServiceAccountMixin):
"""Signs messages with an RSA private key.
Args:
private_key (rsa.key.PrivateKey): 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)
return rsa.pkcs1.sign(message, self._key, "SHA-256")
@classmethod
def from_string(cls, key, key_id=None):
"""Construct an Signer instance from a private key in PEM format.
Args:
key (str): Private key in PEM format.
key_id (str): An optional key id used to identify the private key.
Returns:
google.auth.crypt.Signer: The constructed signer.
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 Python 3
marker_id, key_bytes = pem.readPemBlocksFromFile(
io.StringIO(key), _PKCS1_MARKER, _PKCS8_MARKER
)
# Key is in pkcs1 format.
if marker_id == 0:
private_key = rsa.key.PrivateKey.load_pkcs1(key_bytes, format="DER")
# Key is in pkcs8.
elif marker_id == 1:
key_info, remaining = decoder.decode(key_bytes, asn1Spec=_PKCS8_SPEC)
if remaining != b"":
raise ValueError("Unused bytes", remaining)
private_key_info = key_info.getComponentByName("privateKey")
private_key = rsa.key.PrivateKey.load_pkcs1(
private_key_info.asOctets(), format="DER"
)
else:
raise ValueError("No key could be detected.")
return cls(private_key, key_id=key_id)
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