Adding the CryptographyEngine

This changes adds the CryptographyEngine, which uses pyca/cryptography
to create symmetric and asymmetric keys. A test suite is included.

kmip/core/exceptions.py

@@ -13,6 +13,65 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from kmip.core import enums
+
+
+class KmipError(Exception):
+    """
+    A generic KMIP error that is the base for the KMIP error hierarchy.
+    """
+
+    def __init__(self,
+                 status=enums.ResultStatus.OPERATION_FAILED,
+                 reason=enums.ResultReason.GENERAL_FAILURE,
+                 message='A general failure occurred.'):
+        """
+        Create a KmipError exception.
+
+        Args:
+            status (ResultStatus): An enumeration detailing the result outcome.
+            reason (ResultReason): An enumeration giving the status rationale.
+            message (string): A string containing more information about the
+                error.
+        """
+        super(KmipError, self).__init__(message)
+        self.status = status
+        self.reason = reason
+
+
+class CryptographicFailure(KmipError):
+    """
+    An error generated when problems occur with cryptographic operations.
+    """
+
+    def __init__(self, message):
+        """
+        Create a CryptographicFailure exception.
+
+        Args:
+            message (string): A string containing information about the error.
+        """
+        super(CryptographicFailure, self).__init__(
+            reason=enums.ResultReason.CRYPTOGRAPHIC_FAILURE,
+            message=message)
+
+
+class InvalidField(KmipError):
+    """
+    An error generated when an invalid field value is processed.
+    """
+
+    def __init__(self, message):
+        """
+        Create an InvalidField exception.
+
+        Args:
+            message (string): A string containing information about the error.
+        """
+        super(InvalidField, self).__init__(
+            reason=enums.ResultReason.INVALID_FIELD,
+            message=message)
+
 
 class InvalidKmipEncoding(Exception):
     """