Kwargifiying the splitter for PolicyMessageKit.

nucypher/crypto/kits.py

@@ -15,7 +15,7 @@ You should have received a copy of the GNU Affero General Public License
 along with nucypher.  If not, see <https://www.gnu.org/licenses/>.
 """
 from constant_sorrow.constants import UNKNOWN_SENDER, NOT_SIGNED
-
+from bytestring_splitter import BytestringKwargifier, VariableLengthBytestring
 from nucypher.crypto.splitters import key_splitter, capsule_splitter
 
 
@@ -31,21 +31,18 @@ class CryptoKit:
         if not cls.splitter:
             raise TypeError("This kit doesn't have a splitter defined.")
 
-        return cls.splitter(some_bytes,
-                            return_remainder=cls.return_remainder_when_splitting)
+        splitter = cls.splitter()
+        return splitter(some_bytes)
 
     @classmethod
     def from_bytes(cls, some_bytes):
-        constituents = cls.split_bytes(some_bytes)
-        return cls(*constituents)
+        return cls.split_bytes(some_bytes)
 
 
 class MessageKit(CryptoKit):
     """
     All the components needed to transmit and verify an encrypted message.
     """
-    return_remainder_when_splitting = True
-    splitter = capsule_splitter + key_splitter
 
     def __init__(self,
                  capsule,
@@ -67,15 +64,22 @@ class MessageKit(CryptoKit):
         if include_alice_pubkey and self.sender_verifying_key:
             as_bytes += bytes(self.sender_verifying_key)
 
-        as_bytes += self.ciphertext
+        as_bytes += VariableLengthBytestring(self.ciphertext)
         return as_bytes
 
+    @classmethod
+    def splitter(cls, *args, **kwargs):
+        return BytestringKwargifier(cls,
+                                    capsule=(capsule_splitter, {'single': True}),
+                                    sender_verifying_key=(key_splitter, {'single': True}),
+                                    ciphertext=VariableLengthBytestring)
+
     @property
     def signature(self):
         return self._signature
 
     def __bytes__(self):
-        return bytes(self.capsule) + self.ciphertext
+        return bytes(self.capsule) + VariableLengthBytestring(self.ciphertext)
 
 
 class PolicyMessageKit(MessageKit):