Reject MODE_CTR in Des3 init

Author: JeremiahM37

wolfcrypt/ciphers.py

@@ -628,6 +628,11 @@ class Des3(_Cipher):
         key_size = 24
         _native_type = "Des3 *"
 
+        def __init__(self, key, mode, IV=None):
+            if mode != MODE_CBC:
+                raise ValueError("Des3 only supports MODE_CBC")
+            super().__init__(key, mode, IV)
+
         def _set_key(self, direction):
             if direction == _ENCRYPTION:
                 return _lib.wc_Des3_SetKey(self._enc, self._key,