process xor: skips when key is zero, recognizes 1-byte case

Author: arekbulski

kaitaistruct.py

@@ -336,13 +336,21 @@ def bytes_terminate(data, term, include_term):
 
     @staticmethod
     def process_xor_one(data, key):
+        if key == 0:
+            return data
+
         if PY2:
             return bytes(bytearray(v ^ key for v in bytearray(data)))
         else:
             return bytes(v ^ key for v in data)
 
     @staticmethod
     def process_xor_many(data, key):
+        if len(key) == 1:
+            return KaitaiStream.process_xor_one(data, ord(key))
+        if len(key) <= 64 and key == b'\x00' * len(key):
+            return data
+
         if PY2:
             return bytes(bytearray(a ^ b for a, b in zip(bytearray(data), itertools.cycle(bytearray(key)))))
         else: