dctf_macdonalds2_solution.py

import json
from ptCrypt.Math.base import xor


message = b"\x00" * 16
payload1 = json.dumps({"action": "tag", "message": message.hex()})
print(payload1)
tag = input("tag >> ")
iv = bytes.fromhex(json.loads(tag)["iv"])
ct = bytes.fromhex(json.loads(tag)["ct"])

newMessage = b"\xaa" * 16
newIv = xor(newMessage, iv)

assert xor(newMessage, newIv) == iv
payload2 = json.dumps({"action": "verify", "message": newMessage.hex(), "tag": [newIv.hex(), ct.hex()]})
print(payload2)