Merge pull request #536 from alex/prioritized-multi-backend

Initial work on a prioritized multibackend for which implements CipherBackend

2 files changed, 105 insertions, 2 deletions

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index cb1fee90..d1b95f2a 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -13,12 +13,12 @@
 
 from cryptography.hazmat.backends import openssl
 from cryptography.hazmat.bindings.commoncrypto.binding import (
-    Binding as CCBinding
+    Binding as CommonCryptoBinding
 )
 
 _ALL_BACKENDS = [openssl.backend]
 
-if CCBinding.is_available():
+if CommonCryptoBinding.is_available():
     from cryptography.hazmat.backends import commoncrypto
     _ALL_BACKENDS.append(commoncrypto.backend)
 
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
new file mode 100644
index 00000000..49a4014d
--- /dev/null
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -0,0 +1,103 @@
+# 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
+
+from cryptography import utils
+from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.hazmat.backends.interfaces import (
+    CipherBackend, HashBackend, HMACBackend, PBKDF2HMACBackend
+)
+
+
+@utils.register_interface(CipherBackend)
+@utils.register_interface(HashBackend)
+@utils.register_interface(HMACBackend)
+@utils.register_interface(PBKDF2HMACBackend)
+class MultiBackend(object):
+    name = "multibackend"
+
+    def __init__(self, backends):
+        self._backends = backends
+
+    def _filtered_backends(self, interface):
+        for b in self._backends:
+            if isinstance(b, interface):
+                yield b
+
+    def cipher_supported(self, algorithm, mode):
+        return any(
+            b.cipher_supported(algorithm, mode)
+            for b in self._filtered_backends(CipherBackend)
+        )
+
+    def create_symmetric_encryption_ctx(self, algorithm, mode):
+        for b in self._filtered_backends(CipherBackend):
+            try:
+                return b.create_symmetric_encryption_ctx(algorithm, mode)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
+
+    def create_symmetric_decryption_ctx(self, algorithm, mode):
+        for b in self._filtered_backends(CipherBackend):
+            try:
+                return b.create_symmetric_decryption_ctx(algorithm, mode)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
+
+    def hash_supported(self, algorithm):
+        return any(
+            b.hash_supported(algorithm)
+            for b in self._filtered_backends(HashBackend)
+        )
+
+    def create_hash_ctx(self, algorithm):
+        for b in self._filtered_backends(HashBackend):
+            try:
+                return b.create_hash_ctx(algorithm)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
+
+    def hmac_supported(self, algorithm):
+        return any(
+            b.hmac_supported(algorithm)
+            for b in self._filtered_backends(HMACBackend)
+        )
+
+    def create_hmac_ctx(self, key, algorithm):
+        for b in self._filtered_backends(HMACBackend):
+            try:
+                return b.create_hmac_ctx(key, algorithm)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
+
+    def pbkdf2_hmac_supported(self, algorithm):
+        return any(
+            b.pbkdf2_hmac_supported(algorithm)
+            for b in self._filtered_backends(PBKDF2HMACBackend)
+        )
+
+    def derive_pbkdf2_hmac(self, algorithm, length, salt, iterations,
+                           key_material):
+        for b in self._filtered_backends(PBKDF2HMACBackend):
+            try:
+                return b.derive_pbkdf2_hmac(
+                    algorithm, length, salt, iterations, key_material
+                )
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm