#good_challenges_2021 #PlaidCTF2021 import flag import hashcash import secrets from Crypto.Cipher import AES def gf128(a, b): a = int.from_bytes(a, byteorder="big") b = int.from_bytes(b, byteorder="big") R = 128 P = sum(1 << x for x in [R, 7, 2, 1, 0]) r = 0 for i in range(R): if a & (1 << i): r ^= …