def default_gen_key(cls: MT19937Cipher, mt: MT19937) -> int:
"""
params:
mt: seeded MT19937
returns:
sequence of ints to be used as keystream
"""
generated = list(mt.extract_number().to_bytes(4, byteorder="little"))
byte_index = -1
while True:
byte_index += 1
if byte_index >= 4:
generated = list(mt.extract_number().to_bytes(
4, byteorder="little"))
byte_index = 0
yield generated[byte_index]
def clone_mt19937(mt: MT19937) -> MT19937:
"""
params:
mt: seeded MT19937 generator
returns:
cloned MT19937 with state spliced from that of `mt`
side-effect:
`mt` will have been tapped 624 times
"""
cloned = MT19937()
cloned.index = 0
for i in range(mt.n):
cloned.MT[i] = untemper(mt.extract_number())
return cloned
def test_break_currtime_mt19937_nominal_case(self):
actual_seed = int(time.time())
mt = MT19937()
mt.seed_mt(actual_seed)
cracked_seed = break_currtime_mt19937(mt.extract_number(), eps=10)
self.assertEqual(actual_seed, cracked_seed)
def test_break_currtime_mt19937_seed_outside_search_range_returns_none(
self):
actual_seed = int(time.time()) - 100
mt = MT19937()
mt.seed_mt(actual_seed)
self.assertIsNone(break_currtime_mt19937(mt.extract_number(), eps=10))
def test_untemper_nominal_case(self):
mt = MT19937()
mt.seed_mt(123)
self.assertEqual(untemper(mt.extract_number()), mt.MT[0])
self.assertEqual(untemper(mt.extract_number()), mt.MT[1])
self.assertEqual(untemper(mt.extract_number()), mt.MT[2])
self.assertEqual(untemper(mt.extract_number()), mt.MT[3])
self.assertEqual(untemper(mt.extract_number()), mt.MT[4])
def test_clone_mt19937_nominal_case(self):
mt = MT19937()
mt.seed_mt(123)
cloned_mt = clone_mt19937(mt)
for i in range(mt.n):
cloned_mt.extract_number()
for i in range(5):
self.assertEqual(mt.extract_number(), cloned_mt.extract_number())
def test_default_gen_key_verify_first_two_random_numbers(self):
expected_ints = [254, 205, 75, 178, 109, 61, 132, 182]
mt = MT19937()
mt.seed_mt(123)
actual_ints = []
i = 0
for b in MT19937Cipher.default_gen_key(mt):
actual_ints.append(b)
i += 1
if i == 8:
break
self.assertEqual(expected_ints, actual_ints)
def mt19937_oracle() -> Tuple[int, int]:
"""
Waits a random number of seconds between
Seeds the RNG with the current Unix timestamp
Waits a random number of seconds again.
Returns the first 32 bit output of the RNG and current time used as seed
"""
time.sleep(random.randint(40, 1000))
curr_time = int(time.time())
mt = MT19937()
mt.seed_mt(curr_time)
time.sleep(random.randint(40, 1000))
return mt.extract_number(), curr_time
def encrypt(self: MT19937Cipher, plaintext: bytes) -> bytes:
"""
params:
plaintext: bytes to encrypt
returns:
`plaintext` XORed with keystream generated by `gen_key`
"""
mt = MT19937()
mt.seed_mt(self.seed)
ciphertext = b''
for plain, key in zip(plaintext, self.gen_key(mt)):
ciphertext += (plain ^ key).to_bytes(1, byteorder="little")
return ciphertext
def test_extract_number_nominal_case(self):
# Expected numbers generated from MT19937 with a seed of 123
# obtained from: https://asecuritysite.com/encryption/twister
expected_numbers = (
2991312382,
3062119789,
1228959102,
1840268610,
974319580,
)
mt = MT19937()
mt.seed_mt(123)
for expected in expected_numbers:
self.assertEqual(expected, mt.extract_number())
def break_currtime_mt19937(rand_num: int, eps: int = 1200) -> int:
"""
params:
rand_num: first number generated by MT19937 using current UNIX time
as seed
eps: number of seconds in the past to look back through
returns:
seed used by MT19937 to generate `rand_num`
None if seed not found
"""
curr_time = int(time.time())
for t in range(curr_time - eps, curr_time + 1):
mt = MT19937()
mt.seed_mt(t)
if mt.extract_number() == rand_num:
return t
return None
def test_extract_number_without_seeding_raises(self):
mt = MT19937()
with self.assertRaises(Exception):
mt.extract_number()