From fcaf9761d1a2a570b2249c2ef3fff322dbb0b37b Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:23:57 -0800
Subject: Initial work on a prioritized multibackend for which implements
 CipherBackend

---
 cryptography/hazmat/backends/__init__.py     |  7 +++--
 cryptography/hazmat/backends/multibackend.py | 45 ++++++++++++++++++++++++++++
 tests/conftest.py                            |  5 +++-
 3 files changed, 53 insertions(+), 4 deletions(-)
 create mode 100644 cryptography/hazmat/backends/multibackend.py

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index cb1fee90..b4ef210d 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -12,16 +12,17 @@
 # limitations under the License.
 
 from cryptography.hazmat.backends import openssl
+from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
 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)
 
 
 def default_backend():
-    return openssl.backend
+    return PrioritizedMultiBackend(_ALL_BACKENDS)
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
new file mode 100644
index 00000000..9b91ff45
--- /dev/null
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -0,0 +1,45 @@
+# 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
+
+
+@utils.register_interface(CipherBackend)
+class PrioritizedMultiBackend(object):
+    name = "multibackend"
+
+    def __init__(self, backends):
+        self._backends = backends
+
+    def cipher_supported(self, algorithm, mode):
+        return any(b.cipher_supported(algorithm, mode) for b in self._backends)
+
+    def create_symmetric_encryption_ctx(self, algorithm, mode):
+        for b in self._backends:
+            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._backends:
+            try:
+                return b.create_symmetric_decryption_ctx(algorithm, mode)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
diff --git a/tests/conftest.py b/tests/conftest.py
index ecad1b23..00c44ca9 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,13 +4,16 @@ from cryptography.hazmat.backends import _ALL_BACKENDS
 from cryptography.hazmat.backends.interfaces import (
     HMACBackend, CipherBackend, HashBackend, PBKDF2HMACBackend
 )
+from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
 
 from .utils import check_for_iface, check_backend_support, select_backends
 
 
 def pytest_generate_tests(metafunc):
     names = metafunc.config.getoption("--backend")
-    selected_backends = select_backends(names, _ALL_BACKENDS)
+    selected_backends = select_backends(
+        names, _ALL_BACKENDS + [PrioritizedMultiBackend(_ALL_BACKENDS)]
+    )
 
     if "backend" in metafunc.fixturenames:
         metafunc.parametrize("backend", selected_backends)
-- 
cgit v1.2.3


From 2b8b415a0aadf6a1a1c78a7b474d8b1dbcbc544f Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:32:35 -0800
Subject: HashBackend is now supported by PrioritizedMultiBackend

---
 cryptography/hazmat/backends/multibackend.py | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 9b91ff45..210efbe8 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -15,10 +15,11 @@ from __future__ import absolute_import, division, print_function
 
 from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm
-from cryptography.hazmat.backends.interfaces import CipherBackend
+from cryptography.hazmat.backends.interfaces import CipherBackend, HashBackend
 
 
 @utils.register_interface(CipherBackend)
+@utils.register_interface(HashBackend)
 class PrioritizedMultiBackend(object):
     name = "multibackend"
 
@@ -43,3 +44,14 @@ class PrioritizedMultiBackend(object):
             except UnsupportedAlgorithm:
                 pass
         raise UnsupportedAlgorithm
+
+    def hash_supported(self, algorithm):
+        return any(b.hash_supported(algorithm) for b in self._backends)
+
+    def create_hash_ctx(self, algorithm):
+        for b in self._backends:
+            try:
+                return b.create_hash_ctx(algorithm)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
-- 
cgit v1.2.3


From 2d02857b4b1d6d8adbdd1fa1a753a2c464860bcf Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:36:10 -0800
Subject: Added support for HMAC backend

---
 cryptography/hazmat/backends/multibackend.py | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 210efbe8..035517ea 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -15,11 +15,14 @@ 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
+from cryptography.hazmat.backends.interfaces import (
+    CipherBackend, HashBackend, HMACBackend
+)
 
 
 @utils.register_interface(CipherBackend)
 @utils.register_interface(HashBackend)
+@utils.register_interface(HMACBackend)
 class PrioritizedMultiBackend(object):
     name = "multibackend"
 
@@ -55,3 +58,14 @@ class PrioritizedMultiBackend(object):
             except UnsupportedAlgorithm:
                 pass
         raise UnsupportedAlgorithm
+
+    def hmac_supported(self, algorithm):
+        return any(b.hmac_supported(algorithm) for b in self._backends)
+
+    def create_hmac_ctx(self, key, algorithm):
+        for b in self._backends:
+            try:
+                return b.create_hmac_ctx(key, algorithm)
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
-- 
cgit v1.2.3


From 020ae0fa11bd5e33863b3944ad14bb18ec748645 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:38:43 -0800
Subject: Added PBKDF2HMAC support

---
 cryptography/hazmat/backends/multibackend.py | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 035517ea..e560c7df 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -16,13 +16,14 @@ 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
+    CipherBackend, HashBackend, HMACBackend, PBKDF2HMACBackend
 )
 
 
 @utils.register_interface(CipherBackend)
 @utils.register_interface(HashBackend)
 @utils.register_interface(HMACBackend)
+@utils.register_interface(PBKDF2HMACBackend)
 class PrioritizedMultiBackend(object):
     name = "multibackend"
 
@@ -69,3 +70,17 @@ class PrioritizedMultiBackend(object):
             except UnsupportedAlgorithm:
                 pass
         raise UnsupportedAlgorithm
+
+    def pbkdf2_hmac_supported(self, algorithm):
+        return any(b.pbkdf2_hmac_supported(algorithm) for b in self._backends)
+
+    def derive_pbkdf2_hmac(self, algorithm, length, salt, iterations,
+                           key_material):
+        for b in self._backends:
+            try:
+                return b.derive_pbkdf2_hmac(
+                    algorithm, length, salt, iterations, key_material
+                )
+            except UnsupportedAlgorithm:
+                pass
+        raise UnsupportedAlgorithm
-- 
cgit v1.2.3


From 19e19ae75385f652e1161e1153e9aea599cd6a07 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:46:01 -0800
Subject: Replace re-running all tests with some unit tests

---
 tests/conftest.py                          |  5 +----
 tests/hazmat/backends/test_multibackend.py | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)
 create mode 100644 tests/hazmat/backends/test_multibackend.py

diff --git a/tests/conftest.py b/tests/conftest.py
index 00c44ca9..ecad1b23 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,16 +4,13 @@ from cryptography.hazmat.backends import _ALL_BACKENDS
 from cryptography.hazmat.backends.interfaces import (
     HMACBackend, CipherBackend, HashBackend, PBKDF2HMACBackend
 )
-from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
 
 from .utils import check_for_iface, check_backend_support, select_backends
 
 
 def pytest_generate_tests(metafunc):
     names = metafunc.config.getoption("--backend")
-    selected_backends = select_backends(
-        names, _ALL_BACKENDS + [PrioritizedMultiBackend(_ALL_BACKENDS)]
-    )
+    selected_backends = select_backends(names, _ALL_BACKENDS)
 
     if "backend" in metafunc.fixturenames:
         metafunc.parametrize("backend", selected_backends)
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
new file mode 100644
index 00000000..aaf6d7c1
--- /dev/null
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -0,0 +1,16 @@
+# 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.
+
+
+class TestPrioritizedMultiBackend(object):
+    pass
-- 
cgit v1.2.3


From 6ced2f6444c956b88d42cc61fe9a38751b912c9a Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:53:44 -0800
Subject: Direct tests for the cipher support

---
 tests/hazmat/backends/test_multibackend.py | 50 +++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index aaf6d7c1..dc58a585 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -11,6 +11,54 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import pytest
+
+from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+
+
+class DummyCipherBackend(object):
+    def __init__(self, supported_ciphers):
+        self._ciphers = supported_ciphers
+
+    def cipher_supported(self, algorithm, mode):
+        return (type(algorithm), type(mode)) in self._ciphers
+
+    def create_symmetric_encryption_ctx(self, algorithm, mode):
+        if not self.cipher_supported(algorithm, mode):
+            raise UnsupportedAlgorithm
+
+    def create_symmetric_decryption_ctx(self, algorithm, mode):
+        if not self.cipher_supported(algorithm, mode):
+            raise UnsupportedAlgorithm
+
 
 class TestPrioritizedMultiBackend(object):
-    pass
+    def test_ciphers(self):
+        backend = PrioritizedMultiBackend([
+            DummyCipherBackend([
+                (algorithms.AES, modes.CBC),
+            ])
+        ])
+        assert backend.cipher_supported(
+            algorithms.AES(b"\x00" * 16), modes.CBC(b"\x00" * 16)
+        )
+
+        cipher = Cipher(
+            algorithms.AES(b"\x00" * 16),
+            modes.CBC(b"\x00" * 16),
+            backend=backend
+        )
+        cipher.encryptor()
+        cipher.decryptor()
+
+        cipher = Cipher(
+            algorithms.Camellia(b"\x00" * 16),
+            modes.CBC(b"\x00" * 16),
+            backend=backend
+        )
+        with pytest.raises(UnsupportedAlgorithm):
+            cipher.encryptor()
+        with pytest.raises(UnsupportedAlgorithm):
+            cipher.decryptor()
-- 
cgit v1.2.3


From 87899d4fd55881a4dbec1ee32b79a5bd315ec33f Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:58:40 -0800
Subject: Direct tests for the hash support

---
 tests/hazmat/backends/test_multibackend.py | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index dc58a585..f300b6c8 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -15,6 +15,7 @@ import pytest
 
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
+from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 
 
@@ -34,6 +35,19 @@ class DummyCipherBackend(object):
             raise UnsupportedAlgorithm
 
 
+class DummyHashBackend(object):
+    def __init__(self, supported_algorithms):
+        self._algorithms = supported_algorithms
+
+    def hash_supported(self, algorithm):
+        return type(algorithm) in self._algorithms
+
+    def create_hash_ctx(self, algorithm):
+        if not self.hash_supported(algorithm):
+            raise UnsupportedAlgorithm
+
+
+
 class TestPrioritizedMultiBackend(object):
     def test_ciphers(self):
         backend = PrioritizedMultiBackend([
@@ -62,3 +76,14 @@ class TestPrioritizedMultiBackend(object):
             cipher.encryptor()
         with pytest.raises(UnsupportedAlgorithm):
             cipher.decryptor()
+
+    def test_hashes(self):
+        backend = PrioritizedMultiBackend([
+            DummyHashBackend([hashes.MD5])
+        ])
+        assert backend.hash_supported(hashes.MD5())
+
+        hashes.Hash(hashes.MD5(), backend=backend)
+
+        with pytest.raises(UnsupportedAlgorithm):
+            hashes.Hash(hashes.SHA1(), backend=backend)
-- 
cgit v1.2.3


From b3564a0bf0b93d71adad8d8fef7799bab0e0b67b Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 11:59:55 -0800
Subject: Only make teh default once

---
 cryptography/hazmat/backends/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index b4ef210d..e4fd94ed 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -24,5 +24,6 @@ if CommonCryptoBinding.is_available():
     _ALL_BACKENDS.append(commoncrypto.backend)
 
 
+_default_backend = PrioritizedMultiBackend(_ALL_BACKENDS)
 def default_backend():
-    return PrioritizedMultiBackend(_ALL_BACKENDS)
+    return _default_backend
-- 
cgit v1.2.3


From 723bb9675b7f78e8515be0a80305f6fd009a80fa Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 15:14:25 -0800
Subject: Not true anymore

---
 tests/hazmat/backends/test_openssl.py | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/tests/hazmat/backends/test_openssl.py b/tests/hazmat/backends/test_openssl.py
index f01c3f64..f3b0bb15 100644
--- a/tests/hazmat/backends/test_openssl.py
+++ b/tests/hazmat/backends/test_openssl.py
@@ -40,9 +40,6 @@ class TestOpenSSL(object):
     def test_backend_exists(self):
         assert backend
 
-    def test_is_default(self):
-        assert backend == default_backend()
-
     def test_openssl_version_text(self):
         """
         This test checks the value of OPENSSL_VERSION_TEXT.
-- 
cgit v1.2.3


From 0929f8ff07e71410bd2ce89d407805bd476c1761 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 15:23:17 -0800
Subject: More direct tests

---
 tests/hazmat/backends/test_multibackend.py | 50 +++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index f300b6c8..03b3187b 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -15,8 +15,9 @@ import pytest
 
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
-from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives import hashes, hmac
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
 
 
 class DummyCipherBackend(object):
@@ -47,6 +48,31 @@ class DummyHashBackend(object):
             raise UnsupportedAlgorithm
 
 
+class DummyHMACBackend(object):
+    def __init__(self, supported_algorithms):
+        self._algorithms = supported_algorithms
+
+    def hmac_supported(self, algorithm):
+        return type(algorithm) in self._algorithms
+
+    def create_hmac_ctx(self, key, algorithm):
+        if not self.hmac_supported(algorithm):
+            raise UnsupportedAlgorithm
+
+
+class DummyPBKDF2HMAC(object):
+    def __init__(self, supported_algorithms):
+        self._algorithms = supported_algorithms
+
+    def pbkdf2_hmac_supported(self, algorithm):
+        return type(algorithm) in self._algorithms
+
+    def derive_pbkdf2_hmac(self, algorithm, length, salt, iterations,
+                           key_material):
+        if not self.pbkdf2_hmac_supported(algorithm):
+            raise UnsupportedAlgorithm
+
+
 
 class TestPrioritizedMultiBackend(object):
     def test_ciphers(self):
@@ -87,3 +113,25 @@ class TestPrioritizedMultiBackend(object):
 
         with pytest.raises(UnsupportedAlgorithm):
             hashes.Hash(hashes.SHA1(), backend=backend)
+
+    def test_hmac(self):
+        backend = PrioritizedMultiBackend([
+            DummyHMACBackend([hashes.MD5])
+        ])
+        assert backend.hmac_supported(hashes.MD5())
+
+        hmac.HMAC(b"", hashes.MD5(), backend=backend)
+
+        with pytest.raises(UnsupportedAlgorithm):
+            hmac.HMAC(b"", hashes.SHA1(), backend=backend)
+
+    def test_pbkdf2(self):
+        backend = PrioritizedMultiBackend([
+            DummyPBKDF2HMAC([hashes.MD5])
+        ])
+        assert backend.pbkdf2_hmac_supported(hashes.MD5())
+
+        backend.derive_pbkdf2_hmac(hashes.MD5(), 10, b"", 10, b"")
+
+        with pytest.raises(UnsupportedAlgorithm):
+            backend.derive_pbkdf2_hmac(hashes.SHA1(), 10, b"", 10, b"")
-- 
cgit v1.2.3


From ebc5161f606fe1ac7d51b6ab997f663cfcf9be9b Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Thu, 30 Jan 2014 15:42:37 -0800
Subject: Fix

---
 cryptography/hazmat/backends/multibackend.py | 35 +++++++++++++++++++++-------
 tests/hazmat/backends/test_multibackend.py   | 10 +++++++-
 2 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index e560c7df..94152370 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -30,11 +30,19 @@ class PrioritizedMultiBackend(object):
     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._backends)
+        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._backends:
+        for b in self._filtered_backends(CipherBackend):
             try:
                 return b.create_symmetric_encryption_ctx(algorithm, mode)
             except UnsupportedAlgorithm:
@@ -42,7 +50,7 @@ class PrioritizedMultiBackend(object):
         raise UnsupportedAlgorithm
 
     def create_symmetric_decryption_ctx(self, algorithm, mode):
-        for b in self._backends:
+        for b in self._filtered_backends(CipherBackend):
             try:
                 return b.create_symmetric_decryption_ctx(algorithm, mode)
             except UnsupportedAlgorithm:
@@ -50,10 +58,13 @@ class PrioritizedMultiBackend(object):
         raise UnsupportedAlgorithm
 
     def hash_supported(self, algorithm):
-        return any(b.hash_supported(algorithm) for b in self._backends)
+        return any(
+            b.hash_supported(algorithm)
+            for b in self._filtered_backends(HashBackend)
+        )
 
     def create_hash_ctx(self, algorithm):
-        for b in self._backends:
+        for b in self._filtered_backends(HashBackend):
             try:
                 return b.create_hash_ctx(algorithm)
             except UnsupportedAlgorithm:
@@ -61,10 +72,13 @@ class PrioritizedMultiBackend(object):
         raise UnsupportedAlgorithm
 
     def hmac_supported(self, algorithm):
-        return any(b.hmac_supported(algorithm) for b in self._backends)
+        return any(
+            b.hmac_supported(algorithm)
+            for b in self._filtered_backends(HMACBackend)
+        )
 
     def create_hmac_ctx(self, key, algorithm):
-        for b in self._backends:
+        for b in self._filtered_backends(HMACBackend):
             try:
                 return b.create_hmac_ctx(key, algorithm)
             except UnsupportedAlgorithm:
@@ -72,11 +86,14 @@ class PrioritizedMultiBackend(object):
         raise UnsupportedAlgorithm
 
     def pbkdf2_hmac_supported(self, algorithm):
-        return any(b.pbkdf2_hmac_supported(algorithm) for b in self._backends)
+        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._backends:
+        for b in self._filtered_backends(PBKDF2HMACBackend):
             try:
                 return b.derive_pbkdf2_hmac(
                     algorithm, length, salt, iterations, key_material
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index 03b3187b..127c0d3e 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -13,13 +13,17 @@
 
 import pytest
 
+from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.hazmat.backends.interfaces import (
+    CipherBackend, HashBackend, HMACBackend, PBKDF2HMACBackend
+)
 from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
 from cryptography.hazmat.primitives import hashes, hmac
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
-from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
 
 
+@utils.register_interface(CipherBackend)
 class DummyCipherBackend(object):
     def __init__(self, supported_ciphers):
         self._ciphers = supported_ciphers
@@ -36,6 +40,7 @@ class DummyCipherBackend(object):
             raise UnsupportedAlgorithm
 
 
+@utils.register_interface(HashBackend)
 class DummyHashBackend(object):
     def __init__(self, supported_algorithms):
         self._algorithms = supported_algorithms
@@ -48,6 +53,7 @@ class DummyHashBackend(object):
             raise UnsupportedAlgorithm
 
 
+@utils.register_interface(HMACBackend)
 class DummyHMACBackend(object):
     def __init__(self, supported_algorithms):
         self._algorithms = supported_algorithms
@@ -60,6 +66,7 @@ class DummyHMACBackend(object):
             raise UnsupportedAlgorithm
 
 
+@utils.register_interface(PBKDF2HMACBackend)
 class DummyPBKDF2HMAC(object):
     def __init__(self, supported_algorithms):
         self._algorithms = supported_algorithms
@@ -77,6 +84,7 @@ class DummyPBKDF2HMAC(object):
 class TestPrioritizedMultiBackend(object):
     def test_ciphers(self):
         backend = PrioritizedMultiBackend([
+            DummyHashBackend([]),
             DummyCipherBackend([
                 (algorithms.AES, modes.CBC),
             ])
-- 
cgit v1.2.3


From a45a770f88ad4444c80e52966f5022c4fb287ce5 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 31 Jan 2014 07:51:41 -0800
Subject: pep8 fixes

---
 cryptography/hazmat/backends/__init__.py   | 2 ++
 tests/hazmat/backends/test_multibackend.py | 1 -
 tests/hazmat/backends/test_openssl.py      | 1 -
 3 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index e4fd94ed..0818033f 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -25,5 +25,7 @@ if CommonCryptoBinding.is_available():
 
 
 _default_backend = PrioritizedMultiBackend(_ALL_BACKENDS)
+
+
 def default_backend():
     return _default_backend
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index 127c0d3e..f77d2680 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -80,7 +80,6 @@ class DummyPBKDF2HMAC(object):
             raise UnsupportedAlgorithm
 
 
-
 class TestPrioritizedMultiBackend(object):
     def test_ciphers(self):
         backend = PrioritizedMultiBackend([
diff --git a/tests/hazmat/backends/test_openssl.py b/tests/hazmat/backends/test_openssl.py
index f3b0bb15..0aff41e5 100644
--- a/tests/hazmat/backends/test_openssl.py
+++ b/tests/hazmat/backends/test_openssl.py
@@ -15,7 +15,6 @@ import pytest
 
 from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm, InternalError
-from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.backends.openssl.backend import backend, Backend
 from cryptography.hazmat.primitives import interfaces
 from cryptography.hazmat.primitives.ciphers import Cipher
-- 
cgit v1.2.3


From 450bb4c6609d246ded86959de3d925df81afdba9 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 3 Feb 2014 15:42:04 -0800
Subject: Rename and document

---
 cryptography/hazmat/backends/__init__.py     |  4 ++--
 cryptography/hazmat/backends/multibackend.py |  2 +-
 docs/hazmat/backends/multibackend.rst        | 14 ++++++++++++++
 tests/hazmat/backends/test_multibackend.py   | 12 ++++++------
 4 files changed, 23 insertions(+), 9 deletions(-)
 create mode 100644 docs/hazmat/backends/multibackend.rst

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index 0818033f..41d260a8 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -12,7 +12,7 @@
 # limitations under the License.
 
 from cryptography.hazmat.backends import openssl
-from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
+from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.bindings.commoncrypto.binding import (
     Binding as CommonCryptoBinding
 )
@@ -24,7 +24,7 @@ if CommonCryptoBinding.is_available():
     _ALL_BACKENDS.append(commoncrypto.backend)
 
 
-_default_backend = PrioritizedMultiBackend(_ALL_BACKENDS)
+_default_backend = MultiBackend(_ALL_BACKENDS)
 
 
 def default_backend():
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 94152370..49a4014d 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -24,7 +24,7 @@ from cryptography.hazmat.backends.interfaces import (
 @utils.register_interface(HashBackend)
 @utils.register_interface(HMACBackend)
 @utils.register_interface(PBKDF2HMACBackend)
-class PrioritizedMultiBackend(object):
+class MultiBackend(object):
     name = "multibackend"
 
     def __init__(self, backends):
diff --git a/docs/hazmat/backends/multibackend.rst b/docs/hazmat/backends/multibackend.rst
new file mode 100644
index 00000000..23e6d48f
--- /dev/null
+++ b/docs/hazmat/backends/multibackend.rst
@@ -0,0 +1,14 @@
+.. hazmat::
+
+MultiBackend
+============
+
+.. currentmodule:: cryptography.hazmat.backends.multibackend
+
+.. class:: MultiBackend(backends)
+
+    This class allows you to combine multiple backends into a single backend
+    which offers the combined features of all of its constituents.
+
+    :param backends: A ``list`` of backend objects. Backends are checked for
+                     feature support in the other they exist in this list.
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index f77d2680..ca21c9fc 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -18,7 +18,7 @@ from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.backends.interfaces import (
     CipherBackend, HashBackend, HMACBackend, PBKDF2HMACBackend
 )
-from cryptography.hazmat.backends.multibackend import PrioritizedMultiBackend
+from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.primitives import hashes, hmac
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 
@@ -80,9 +80,9 @@ class DummyPBKDF2HMAC(object):
             raise UnsupportedAlgorithm
 
 
-class TestPrioritizedMultiBackend(object):
+class TestMultiBackend(object):
     def test_ciphers(self):
-        backend = PrioritizedMultiBackend([
+        backend = MultiBackend([
             DummyHashBackend([]),
             DummyCipherBackend([
                 (algorithms.AES, modes.CBC),
@@ -111,7 +111,7 @@ class TestPrioritizedMultiBackend(object):
             cipher.decryptor()
 
     def test_hashes(self):
-        backend = PrioritizedMultiBackend([
+        backend = MultiBackend([
             DummyHashBackend([hashes.MD5])
         ])
         assert backend.hash_supported(hashes.MD5())
@@ -122,7 +122,7 @@ class TestPrioritizedMultiBackend(object):
             hashes.Hash(hashes.SHA1(), backend=backend)
 
     def test_hmac(self):
-        backend = PrioritizedMultiBackend([
+        backend = MultiBackend([
             DummyHMACBackend([hashes.MD5])
         ])
         assert backend.hmac_supported(hashes.MD5())
@@ -133,7 +133,7 @@ class TestPrioritizedMultiBackend(object):
             hmac.HMAC(b"", hashes.SHA1(), backend=backend)
 
     def test_pbkdf2(self):
-        backend = PrioritizedMultiBackend([
+        backend = MultiBackend([
             DummyPBKDF2HMAC([hashes.MD5])
         ])
         assert backend.pbkdf2_hmac_supported(hashes.MD5())
-- 
cgit v1.2.3


From 7ceacba2f3c24e7333bf9af901541055bb3a51ab Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 3 Feb 2014 15:50:03 -0800
Subject: Added to toctree

---
 docs/hazmat/backends/index.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/hazmat/backends/index.rst b/docs/hazmat/backends/index.rst
index dbc0724e..983a44e9 100644
--- a/docs/hazmat/backends/index.rst
+++ b/docs/hazmat/backends/index.rst
@@ -32,4 +32,5 @@ Individual Backends
 
     openssl
     commoncrypto
+    multibackend
     interfaces
-- 
cgit v1.2.3


From 2b1752ed68a08255ddacf1800c6cb6b406ce5e4b Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 3 Feb 2014 16:11:23 -0800
Subject: Typo fix

---
 docs/hazmat/backends/multibackend.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/hazmat/backends/multibackend.rst b/docs/hazmat/backends/multibackend.rst
index 23e6d48f..971c7671 100644
--- a/docs/hazmat/backends/multibackend.rst
+++ b/docs/hazmat/backends/multibackend.rst
@@ -11,4 +11,4 @@ MultiBackend
     which offers the combined features of all of its constituents.
 
     :param backends: A ``list`` of backend objects. Backends are checked for
-                     feature support in the other they exist in this list.
+                     feature support in the order they appear in this list.
-- 
cgit v1.2.3


From 559885087728c0233b243756fe698e4071fab971 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 3 Feb 2014 16:15:06 -0800
Subject: Added an example usage

---
 cryptography/hazmat/backends/__init__.py |  6 +-----
 docs/hazmat/backends/multibackend.rst    | 12 ++++++++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index 41d260a8..d1b95f2a 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -12,7 +12,6 @@
 # limitations under the License.
 
 from cryptography.hazmat.backends import openssl
-from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.bindings.commoncrypto.binding import (
     Binding as CommonCryptoBinding
 )
@@ -24,8 +23,5 @@ if CommonCryptoBinding.is_available():
     _ALL_BACKENDS.append(commoncrypto.backend)
 
 
-_default_backend = MultiBackend(_ALL_BACKENDS)
-
-
 def default_backend():
-    return _default_backend
+    return openssl.backend
diff --git a/docs/hazmat/backends/multibackend.rst b/docs/hazmat/backends/multibackend.rst
index 971c7671..f1a88006 100644
--- a/docs/hazmat/backends/multibackend.rst
+++ b/docs/hazmat/backends/multibackend.rst
@@ -10,5 +10,17 @@ MultiBackend
     This class allows you to combine multiple backends into a single backend
     which offers the combined features of all of its constituents.
 
+    .. code-block:: pycon
+
+        >>> from cryptography.hazmat.backends.multibackend import MultiBackend
+        >>> from cryptography.hazmat.primitives import hashes
+        >>> backend1.hash_supported(hashes.SHA256())
+        False
+        >>> backend2.hash_supported(hashes.SHA1())
+        True
+        >>> multi_backend = MultiBackend([backend1, backend2])
+        >>> multi_backend.hash_supported(hashes.SHA1())
+        True
+
     :param backends: A ``list`` of backend objects. Backends are checked for
                      feature support in the order they appear in this list.
-- 
cgit v1.2.3


From db80954cf1448f88fae78568dbd3d833da04054a Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 3 Feb 2014 16:19:32 -0800
Subject: Chanloge + versionadded

---
 docs/changelog.rst                    | 1 +
 docs/hazmat/backends/multibackend.rst | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 2de9a329..e322b145 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -16,6 +16,7 @@ Changelog
   available, such as CentOS.
 * Added :class:`~cryptography.hazmat.primitives.kdf.pbkdf2.PBKDF2HMAC`.
 * Added :class:`~cryptography.hazmat.primitives.kdf.hkdf.HKDF`.
+* Added :doc:`/hazmat/backends/multibackend`.
 
 0.1 - 2014-01-08
 ~~~~~~~~~~~~~~~~
diff --git a/docs/hazmat/backends/multibackend.rst b/docs/hazmat/backends/multibackend.rst
index f1a88006..63177bef 100644
--- a/docs/hazmat/backends/multibackend.rst
+++ b/docs/hazmat/backends/multibackend.rst
@@ -7,6 +7,8 @@ MultiBackend
 
 .. class:: MultiBackend(backends)
 
+    .. versionadded:: 0.2
+
     This class allows you to combine multiple backends into a single backend
     which offers the combined features of all of its constituents.
 
-- 
cgit v1.2.3