challenge19.py

import challenge18 as c18
import challenge3 as c3
import challenge12 as c12
import challenge2 as c2
import base64
from freq import frequency

key = c12.randbytes(16)
nonce = 0


def encrypt(plaintext):

    return c18.AES_CTR(plaintext, key, mode="dec")


def transpose_cyphers(cyphers):

    max_len = max(map(len, cyphers))

    c_t = [[c[i] for c in cyphers if len(c) > i] for i in range(max_len)]
    return c_t


def get_keystream(cyphers):

    cypher_t = transpose_cyphers(cyphers)
    keystream = b"".join([c3.check_all_chars(x)[0] for x in cypher_t])

    return keystream


if __name__ == "__main__":

    with open("data/19.txt", "r") as f:
        text = f.read().split("\n")[:-1]

    plaintexts = [base64.b64decode(i) for i in text]

    cyphertexts = [encrypt(p) for p in plaintexts]
    keystream = get_keystream(cyphertexts)

    decyphered = [c2.fixed_xor(c, keystream) for c in cyphertexts]