Add cryptography-based RSA signer and verifier. (#185)

Fixes #183.

.gitignore

@@ -12,6 +12,7 @@ docs/_build
 .nox/
 .tox/
 .cache/
+.pytest_cache/
 
 # Django test database
 db.sqlite3

google/auth/crypt/_cryptography_rsa.py

@@ -0,0 +1,137 @@
+# 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.
+
+"""RSA verifier and signer that use the ``cryptography`` library.
+
+This is a much faster implementation than the default (in
+``google.auth.crypt._python_rsa``), which depends on the pure-Python
+``rsa`` library.
+"""
+
+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 padding
+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()
+_SHA256 = hashes.SHA256()
+
+
+class RSAVerifier(base.Verifier):
+    """Verifies RSA cryptographic signatures using public keys.
+
+    Args:
+        public_key (
+                cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey):
+            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:
+            self._pubkey.verify(signature, message, _PADDING, _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 RSASigner(base.Signer, base.FromServiceAccountMixin):
+    """Signs messages with an RSA private key.
+
+    Args:
+        private_key (
+                cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey):
+            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 self._key.sign(
+            message, _PADDING, _SHA256)
+
+    @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)

google/auth/crypt/_python_rsa.py

@@ -21,9 +21,6 @@
 
 from __future__ import absolute_import
 
-import io
-import json
-
 from pyasn1.codec.der import decoder
 from pyasn1_modules import pem
 from pyasn1_modules.rfc2459 import Certificate
@@ -41,8 +38,6 @@
 _PKCS8_MARKER = ('-----BEGIN PRIVATE KEY-----',
                  '-----END PRIVATE KEY-----')
 _PKCS8_SPEC = PrivateKeyInfo()
-_JSON_FILE_PRIVATE_KEY = 'private_key'
-_JSON_FILE_PRIVATE_KEY_ID = 'private_key_id'
 
 
 def _bit_list_to_bytes(bit_list):
@@ -119,7 +114,7 @@ def from_string(cls, public_key):
         return cls(pubkey)
 
 
-class RSASigner(base.Signer):
+class RSASigner(base.Signer, base.FromServiceAccountMixin):
     """Signs messages with an RSA private key.
 
     Args:
@@ -179,43 +174,3 @@ def from_string(cls, key, key_id=None):
             raise ValueError('No key could be detected.')
 
         return cls(private_key, key_id=key_id)
-
-    @classmethod
-    def from_service_account_info(cls, info):
-        """Creates a Signer instance instance from a dictionary containing
-        service account info in Google format.
-
-        Args:
-            info (Mapping[str, str]): The service account info in Google
-                format.
-
-        Returns:
-            google.auth.crypt.Signer: The constructed signer.
-
-        Raises:
-            ValueError: If the info is not in the expected format.
-        """
-        if _JSON_FILE_PRIVATE_KEY not in info:
-            raise ValueError(
-                'The private_key field was not found in the service account '
-                'info.')
-
-        return cls.from_string(
-            info[_JSON_FILE_PRIVATE_KEY],
-            info.get(_JSON_FILE_PRIVATE_KEY_ID))
-
-    @classmethod
-    def from_service_account_file(cls, filename):
-        """Creates a Signer instance from a service account .json file
-        in Google format.
-
-        Args:
-            filename (str): The path to the service account .json file.
-
-        Returns:
-            google.auth.crypt.Signer: The constructed signer.
-        """
-        with io.open(filename, 'r', encoding='utf-8') as json_file:
-            data = json.load(json_file)
-
-        return cls.from_service_account_info(data)

google/auth/crypt/base.py

@@ -15,10 +15,16 @@
 """Base classes for cryptographic signers and verifiers."""
 
 import abc
+import io
+import json
 
 import six
 
 
+_JSON_FILE_PRIVATE_KEY = 'private_key'
+_JSON_FILE_PRIVATE_KEY_ID = 'private_key_id'
+
+
 @six.add_metaclass(abc.ABCMeta)
 class Verifier(object):
     """Abstract base class for crytographic signature verifiers."""
@@ -62,3 +68,64 @@ def sign(self, message):
         # pylint: disable=missing-raises-doc,redundant-returns-doc
         # (pylint doesn't recognize that this is abstract)
         raise NotImplementedError('Sign must be implemented')
+
+
+@six.add_metaclass(abc.ABCMeta)
+class FromServiceAccountMixin(object):
+    """Mix-in to enable factory constructors for a Signer."""
+
+    @abc.abstractmethod
+    def from_string(cls, key, key_id=None):
+        """Construct an Signer instance from a private key string.
+
+        Args:
+            key (str): Private key as a string.
+            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.
+        """
+        raise NotImplementedError('from_string must be implemented')
+
+    @classmethod
+    def from_service_account_info(cls, info):
+        """Creates a Signer instance instance from a dictionary containing
+        service account info in Google format.
+
+        Args:
+            info (Mapping[str, str]): The service account info in Google
+                format.
+
+        Returns:
+            google.auth.crypt.Signer: The constructed signer.
+
+        Raises:
+            ValueError: If the info is not in the expected format.
+        """
+        if _JSON_FILE_PRIVATE_KEY not in info:
+            raise ValueError(
+                'The private_key field was not found in the service account '
+                'info.')
+
+        return cls.from_string(
+            info[_JSON_FILE_PRIVATE_KEY],
+            info.get(_JSON_FILE_PRIVATE_KEY_ID))
+
+    @classmethod
+    def from_service_account_file(cls, filename):
+        """Creates a Signer instance from a service account .json file
+        in Google format.
+
+        Args:
+            filename (str): The path to the service account .json file.
+
+        Returns:
+            google.auth.crypt.Signer: The constructed signer.
+        """
+        with io.open(filename, 'r', encoding='utf-8') as json_file:
+            data = json.load(json_file)
+
+        return cls.from_service_account_info(data)

google/auth/crypt/rsa.py

@@ -14,7 +14,17 @@
 
 """RSA cryptography signer and verifier."""
 
-from google.auth.crypt import _python_rsa
 
-RSASigner = _python_rsa.RSASigner
-RSAVerifier = _python_rsa.RSAVerifier
+try:
+    # Prefer cryptograph-based RSA implementation.
+    from google.auth.crypt import _cryptography_rsa
+
+    RSASigner = _cryptography_rsa.RSASigner
+    RSAVerifier = _cryptography_rsa.RSAVerifier
+except ImportError:  # pragma: NO COVER
+    # Fallback to pure-python RSA implementation if cryptography is
+    # unavailable.
+    from google.auth.crypt import _python_rsa
+
+    RSASigner = _python_rsa.RSASigner
+    RSAVerifier = _python_rsa.RSAVerifier