Merge pull request #931 from Ayrx/cmac-implementation

CMAC implementation and docs

1 files changed, 75 insertions, 0 deletions

diff --git a/cryptography/hazmat/primitives/cmac.py b/cryptography/hazmat/primitives/cmac.py
new file mode 100644
index 00000000..7e7f65ab
--- /dev/null
+++ b/cryptography/hazmat/primitives/cmac.py
@@ -0,0 +1,75 @@
+# 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 six
+
+from cryptography import utils
+from cryptography.exceptions import (
+    AlreadyFinalized, InvalidSignature, UnsupportedAlgorithm, _Reasons
+)
+from cryptography.hazmat.backends.interfaces import CMACBackend
+from cryptography.hazmat.primitives import constant_time, interfaces
+
+
+@utils.register_interface(interfaces.CMACContext)
+class CMAC(object):
+    def __init__(self, algorithm, backend, ctx=None):
+        if not isinstance(backend, CMACBackend):
+            raise UnsupportedAlgorithm(
+                "Backend object does not implement CMACBackend",
+                _Reasons.BACKEND_MISSING_INTERFACE
+            )
+
+        if not isinstance(algorithm, interfaces.BlockCipherAlgorithm):
+            raise TypeError(
+                "Expected instance of interfaces.BlockCipherAlgorithm"
+            )
+        self._algorithm = algorithm
+
+        self._backend = backend
+        if ctx is None:
+            self._ctx = self._backend.create_cmac_ctx(self._algorithm)
+        else:
+            self._ctx = ctx
+
+    def update(self, data):
+        if self._ctx is None:
+            raise AlreadyFinalized("Context was already finalized")
+        if isinstance(data, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before hashing")
+        self._ctx.update(data)
+
+    def finalize(self):
+        if self._ctx is None:
+            raise AlreadyFinalized("Context was already finalized")
+        digest = self._ctx.finalize()
+        self._ctx = None
+        return digest
+
+    def verify(self, signature):
+        if isinstance(signature, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before verifying")
+        digest = self.finalize()
+        if not constant_time.bytes_eq(digest, signature):
+            raise InvalidSignature("Signature did not match digest.")
+
+    def copy(self):
+        if self._ctx is None:
+            raise AlreadyFinalized("Context was already finalized")
+        return CMAC(
+            self._algorithm,
+            backend=self._backend,
+            ctx=self._ctx.copy()
+        )