Merge pull request #269 from dreid/backend-interfaces

Backend interfaces

4 files changed, 210 insertions, 0 deletions

diff --git a/cryptography/hazmat/bindings/interfaces.py b/cryptography/hazmat/bindings/interfaces.py
new file mode 100644
index 00000000..912476bb
--- /dev/null
+++ b/cryptography/hazmat/bindings/interfaces.py
@@ -0,0 +1,66 @@
+# 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.
+
+from __future__ import absolute_import, division, print_function
+
+import abc
+
+import six
+
+
+class CipherBackend(six.with_metaclass(abc.ABCMeta)):
+    @abc.abstractmethod
+    def cipher_supported(self, cipher, mode):
+        """
+        Return True if the given cipher and mode are supported.
+        """
+
+    @abc.abstractmethod
+    def register_cipher_adapter(self, cipher, mode, adapter):
+        """
+        Register an adapter for a cipher and mode to a backend specific object.
+        """
+
+    @abc.abstractmethod
+    def create_symmetric_encryption_ctx(self, cipher, mode):
+        """
+        Get a CipherContext that can be used for encryption.
+        """
+
+    @abc.abstractmethod
+    def create_symmetric_decryption_ctx(self, cipher, mode):
+        """
+        Get a CipherContext that can be used for decryption.
+        """
+
+
+class HashBackend(six.with_metaclass(abc.ABCMeta)):
+    @abc.abstractmethod
+    def hash_supported(self, algorithm):
+        """
+        Return True if the hash algorithm is supported by this backend.
+        """
+
+    @abc.abstractmethod
+    def create_hash_ctx(self, algorithm):
+        """
+        Create a HashContext for calculating a message digest.
+        """
+
+
+class HMACBackend(six.with_metaclass(abc.ABCMeta)):
+    @abc.abstractmethod
+    def create_hmac_ctx(self, key, algorithm):
+        """
+        Create a HashContext for calculating a message authentication code.
+        """
diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 92cd3868..db4d18e7 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -20,6 +20,9 @@ import cffi
 
 from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.hazmat.bindings.interfaces import (
+    CipherBackend, HashBackend, HMACBackend
+)
 from cryptography.hazmat.primitives import interfaces
 from cryptography.hazmat.primitives.ciphers.algorithms import (
     AES, Blowfish, Camellia, CAST5, TripleDES, ARC4,
@@ -29,6 +32,9 @@ from cryptography.hazmat.primitives.ciphers.modes import (
 )
 
 
+@utils.register_interface(CipherBackend)
+@utils.register_interface(HashBackend)
+@utils.register_interface(HMACBackend)
 class Backend(object):
     """
     OpenSSL API wrapper.
diff --git a/docs/hazmat/bindings/index.rst b/docs/hazmat/bindings/index.rst
index 19e03999..11355bfa 100644
--- a/docs/hazmat/bindings/index.rst
+++ b/docs/hazmat/bindings/index.rst
@@ -7,3 +7,4 @@ Bindings
     :maxdepth: 1
 
     openssl
+    interfaces
diff --git a/docs/hazmat/bindings/interfaces.rst b/docs/hazmat/bindings/interfaces.rst
new file mode 100644
index 00000000..c55d86dc
--- /dev/null
+++ b/docs/hazmat/bindings/interfaces.rst
@@ -0,0 +1,137 @@
+.. hazmat::
+
+Backend Interfaces
+==================
+
+.. currentmodule:: cryptography.hazmat.bindings.interfaces
+
+
+Backend implementations may provide a number of interfaces to support operations
+such as :doc:`/hazmat/primitives/symmetric-encryption`,
+:doc:`/hazmat/primitives/cryptographic-hashes`, and
+:doc:`/hazmat/primitives/hmac`.
+
+A specific ``backend`` may provide one or more of these interfaces.
+
+
+.. class:: CipherBackend
+
+    A backend which provides methods for using ciphers for encryption
+    and decryption.
+
+    .. method:: cipher_supported(cipher, mode)
+
+        Check if a ``cipher`` and ``mode`` combination is supported by
+        this backend.
+
+        :param cipher: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
+            provider.
+        :param mode: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
+
+        :returns: ``True`` if the specified ``cipher`` and ``mode`` combination
+            is supported by this backend, otherwise ``False``
+
+    .. method:: register_cipher_adapter(cipher_cls, mode_cls, adapter)
+
+        Register an adapter which can be used to create a backend specific
+        object from instances of the
+        :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm` and
+        the :class:`~cryptography.hazmat.primitives.interfaces.Mode` primitives.
+
+        :param cipher_cls: A class whose instances provide
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
+        :param mode_cls: A class whose instances provide:
+            :class:`~cryptography.hazmat.primitives.interfaces.Mode`
+        :param adapter: A ``function`` that takes 3 arguments, ``backend`` (a
+            :class:`CipherBackend` provider), ``cipher`` (a
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
+            provider ), and ``mode`` (a
+            :class:`~cryptography.hazmat.primitives.interfaces.Mode` provider).
+            It returns a backend specific object which may be used to construct
+            a :class:`~cryptogrpahy.hazmat.primitives.interfaces.CipherContext`.
+
+
+    .. method:: create_symmetric_encryption_ctx(cipher, mode)
+
+        Create a
+        :class:`~cryptogrpahy.hazmat.primitives.interfaces.CipherContext` that
+        can be used for encrypting data with the symmetric ``cipher`` using
+        the given ``mode``.
+
+        :param cipher: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
+            provider.
+        :param mode: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherContext`
+
+
+    .. method:: create_symmetric_decryption_ctx(cipher, mode)
+
+        Create a
+        :class:`~cryptogrpahy.hazmat.primitives.interfaces.CipherContext` that
+        can be used for decrypting data with the symmetric ``cipher`` using
+        the given ``mode``.
+
+        :param cipher: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
+            provider.
+        :param mode: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.CipherContext`
+
+
+.. class:: HashBackend
+
+    A backend with methods for using cryptographic hash functions.
+
+    .. method:: hash_supported(algorithm)
+
+        Check if the specified ``algorithm`` is supported by this backend.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :returns: ``True`` if the specified ``algorithm`` is supported by this
+            backend, otherwise ``False``.
+
+
+    .. method:: create_hash_ctx(algorithm)
+
+        Create a
+        :class:`~cryptogrpahy.hazmat.primitives.interfaces.HashContext` that
+        uses the specified ``algorithm`` to calculate a message digest.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.HashContext`
+
+
+.. class:: HMACBackend
+
+    A backend with methods for using cryptographic hash functions as message
+    authentication codes.
+
+    .. method:: create_hmac_ctx(algorithm)
+
+        Create a
+        :class:`~cryptogrpahy.hazmat.primitives.interfaces.HashContext` that
+        uses the specified ``algorithm`` to calculate a hash-based message
+        authentication code.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.HashContext`