key_cracker.py

def rev_multiply(ciphertexts):
    candidates, noncandidates = condition1(ciphertexts)
    gcdd, key_scaler, _ = egcd(diff, 1 << 64)
    keycounter = Counter()

    for cand in candidates:
        ci1, ci2 = map(int, cand, repeat(16))

        if (ci1 + ci2) % 2 != 0 or ci1 ^ ci2 == diff:
            continue

        kodd = (((ci1 + ci2) // gcdd) * key_scaler) % (1 << 64)
        kcomp = int(''.join(comp(list(f'{kodd:064b}'), 0)), 2)

        keycounter[kodd] += 1
        keycounter[kcomp] += 1

    return keycounter.most_common(1)


def crack_subkey(ciphertexts):
    conf = 0
    k_pair = rev_multiply(ciphertexts)
    if len(k_pair) < 1:
        return None
    k_odd, conf = k_pair[0]
    # Cracking the subkey is a deterministic process
    # If the confidence in the calculated subkey is too low, we have to try
    # different keys
    if conf <= 1:
        return None
    kcomp = int(''.join(comp(list(f'{k_odd:064b}'), 0)), 2)
    return [k_odd, kcomp, k_odd ^ 1, kcomp ^ 1]