Added Wycheproof tests for AES-SIV

lib/Crypto/Protocol/KDF.py

@@ -189,7 +189,10 @@ class _S2V(object):
         self._key = _copy_bytes(None, None, key)
         self._ciphermod = ciphermod
         self._last_string = self._cache = b'\x00' * ciphermod.block_size
+        
+        # Max number of update() call we can process
         self._n_updates = ciphermod.block_size * 8 - 1
+        
         if cipher_params is None:
             self._cipher_params = {}
         else:
@@ -224,12 +227,8 @@ class _S2V(object):
           item : byte string
             The next component of the vector.
         :Raise TypeError: when the limit on the number of components has been reached.
-        :Raise ValueError: when the component is empty
         """
 
-        if not item:
-            raise ValueError("A component cannot be empty")
-
         if self._n_updates == 0:
             raise TypeError("Too many components passed to S2V")
         self._n_updates -= 1
@@ -248,8 +247,10 @@ class _S2V(object):
         """
 
         if len(self._last_string) >= 16:
+            # xorend
             final = self._last_string[:-16] + strxor(self._last_string[-16:], self._cache)
         else:
+            # zero-pad & xor
             padded = (self._last_string + b'\x80' + b'\x00' * 15)[:16]
             final = strxor(padded, self._double(self._cache))
         mac = CMAC.new(self._key,