def crypt(plaintext, seed):
mt = MersenneTwister(seed)
keystream = b""
for i in range(0, len(plaintext), 4):
keystream += mt.extract_number().to_bytes(length=4, byteorder="little")
return xor(plaintext, keystream)
def extract_key(ciphertext, decrypter):
ciphertext = list(ciphertext)
ciphertext[16:32] = [0] * 16
ciphertext = bytes(ciphertext)
try:
decrypter(ciphertext)
except InvalidASCII as e:
plaintext = e.args[0]
return xor(plaintext[:16], plaintext[32:48])
def cbc_decrypt(ciphertext, key, iv=(b"\x00" * 16)):
cipher = AES.new(key, mode=AES.MODE_ECB)
plaintext = b""
prevblock = iv
for i in range(0, len(ciphertext), 16):
cipherblock = ciphertext[i:i + 16]
plainblock = xor(cipher.decrypt(cipherblock), prevblock)
plaintext += plainblock
prevblock = cipherblock
return plaintext
def cbc_encrypt(plaintext, key, iv=(b"\x00" * 16)):
cipher = AES.new(key, mode=AES.MODE_ECB)
ciphertext = b""
prevblock = iv
for i in range(0, len(plaintext), 16):
plainblock = pkcs7_pad(plaintext[i:i + 16])
cipherblock = cipher.encrypt(xor(prevblock, plainblock))
ciphertext += cipherblock
prevblock = cipherblock
return ciphertext
def solve_ciphertexts(ciphertexts):
ct_length, trunc_ciphertexts = truncate_ciphertexts(ciphertexts)
transposed_cts = transpose_blocks(trunc_ciphertexts, ct_length)
keystream = bytes(
select_option(get_options(block))[0] for block in transposed_cts)
return [xor(cycle(keystream), ct) for ct in trunc_ciphertexts]
def ctr_crypt(text, key, nonce):
return xor(text, get_keystream(key, nonce, len(text)))