update writeup

crypto/XMASSpirit/README.md

@@ -43,11 +43,11 @@ def get_factors(ct:bytes, n:int=256) -> (int, int):
 - When the factors are found, simply create a lookup table of all values and substitute each byte in the ciphertext.
 
 ```python
-def decrypt(ct:bytes) -> bytes:
+def decrypt(ct:bytes, lut:dict) -> bytes:
     ''' decrypt the file using the lookup table '''
     res = b''
     for byte in ct:
-        dec = lookup[byte]
+        dec = lut[byte]
         res += bytes([dec])
     return res
 ```