def simulate_communication_with_dh_key(prime, base):
""" Simulates a communication between two parties who first exhanges key via
diffiehillman and encrypt messages using aes_cbc. Returns two messages, one
encrypted by each party
"""
alice = {}
alice['dh'] = DiffieHellman(prime, base, secret_key=secrets.randbelow(prime))
alice_pub = alice['dh'].gen_public_key()
#bob recieves alice's public key, generates their own public key and
#the shared key. Sends their public key ot alice
bob = {'dh':DiffieHellman(prime, base, secret_key=secrets.randbelow(prime))}
bob_pub = bob['dh'].gen_public_key()
bob['dh'].gen_shared_key(alice_pub)
### Alice recieves Bob's public key, generates the shared key and encrypts
### message for bob
alice['dh'].gen_shared_key(bob_pub)
alice['message'] = b'Message to Bob'
alice['sha1'] = SHA1(bso.int_to_bytes(alice['dh'].shared_key))
alice['cipher'] = AES_CBC(alice['sha1'].digest()[:16], secrets.token_bytes(16))
alice_ciphertext = alice['cipher'].encrypt(alice['message'])
alice_ciphertext += alice['cipher'].IV
#Bob encrypts his own ciphertext.
bob['message'] = b'Message to Alice'
bob['sha1'] = SHA1(bso.int_to_bytes(bob['dh'].shared_key))
bob['cipher'] = AES_CBC(bob['sha1'].digest()[:16], secrets.token_bytes(16))
bob_ciphertext = bob['cipher'].encrypt(bob['message'])
bob_ciphertext += bob['cipher'].IV
### Check decryption works
assert(bso.remove_padding_pkcs7(alice['cipher'].decrypt(bob_ciphertext[:-16], bob_ciphertext[-16:])) == bob['message'])
assert(bso.remove_padding_pkcs7(bob['cipher'].decrypt(alice_ciphertext[:-16], alice_ciphertext[-16:])) == alice['message'])
## return ciphertexts for the man in the middle to decrypt
return alice_ciphertext, bob_ciphertext
def check_padding(self, ciphertext, IV=None):
"""Decrypts and attemts to remove padding. If the padding is invalid
raises an exception. Returns true otherwise"""
plaintext = AES_CBC_random.decrypt(self, ciphertext, IV)
plaintext = bso.remove_padding_pkcs7(plaintext)
return True
def main():
prime = 0xffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552bb9ed529077096966d670c354e4abc9804f1746c08ca237327ffffffffffffffff
for base in [1, prime, prime - 1]:
messages = simulate_communication_with_dh_key(prime, base)
if base == prime:
secret_key = 0
else:
secret_key = 1
aes_key = SHA1(bso.int_to_bytes(secret_key)).digest()[:16]
malcolm = AES_CBC(aes_key, b'0'*16)
assert bso.remove_padding_pkcs7(malcolm.decrypt(messages[0][:-16], messages[0][-16:])) == b'Message to Bob'
assert bso.remove_padding_pkcs7(malcolm.decrypt(messages[1][:-16], messages[1][-16:])) == b'Message to Alice'
def main():
"""Simulate a man in the middle attack on Diffie Hellman key exchange"""
prime = 0xffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552bb9ed529077096966d670c354e4abc9804f1746c08ca237327ffffffffffffffff
base = 2
connection = diffiehellman_mitm_sim(prime, base)
# intercept alices public key
prime, base, _ = next(connection)
# send prime instead of alices public key to bob. Recieve Bobs public key,
# which we forget as it is not needs. The shared kill will be 0.
connection.send((prime, base, prime))
#Send prime as bob's public key to alice. We have ensured that the shared
#hared secret key is 0. Recieve Alice's ciphertext for bob
ciphertext_a2b = connection.send(prime)
# decrypt
malcolm = AES_CBC(SHA1(bso.int_to_bytes(0)).digest()[:16], b'0' * 16)
messages = []
messages.append(
bso.remove_padding_pkcs7(
malcolm.decrypt(ciphertext_a2b[:-16], ciphertext_a2b[-16:])))
#Send the ciphertext to bob. Recieve his response
ciphertext_b2a = connection.send(ciphertext_a2b)
messages.append(
bso.remove_padding_pkcs7(
malcolm.decrypt(ciphertext_b2a[:-16], ciphertext_b2a[-16:])))
assert messages[0] == b'Message to Bob'
assert messages[1] == b'Message to Alice'
return
def main():
tests = [
b"ICE ICE BABY\x04\x04\x04\x04", b"ICE ICE BABY\x05\x05\x05\x05",
b"ICE ICE BABY\x01\x02\x04\x04"
]
for test in tests:
try:
depadded = bso.remove_padding_pkcs7(test)
assert depadded == b'ICE ICE BABY'
except Exception as e:
assert test in [
b"ICE ICE BABY\x05\x05\x05\x05",
b"ICE ICE BABY\x01\x02\x04\x04"
]
def decrypt(self, ciphertext):
plaintext = AES_CBC.decrypt(self, ciphertext)
plaintext = bso.remove_padding_pkcs7(plaintext)
return plaintext
def decrypt(self, ciphertext):
plaintext = AES_ECB_random.decrypt(self, ciphertext)
plaintext = bso.remove_padding_pkcs7(plaintext)
return stringops.kequalsv_to_dict(plaintext.decode())
