def print_texts(self):
print("key {} texts:".format(self.identifier))
for pair in self.texts:
if 'cipher' in pair:
print("Ciphertext: {}".format(hex(pair['cipher'])), end=", ")
else:
print("Ciphertext: null", end=", ")
if 'plain' in pair:
print("Plaintext: {} (\"{}\")".format(
hex(pair['plain']), i2b(pair['plain'], size=self.size)))
else:
print("Plaintext: null")
def verify_bleichenbacher_middle(message, signature, key, hash_function='sha1'):
"""00 01 garbage 00 ANS1 HASH"""
hash_msg = getattr(hashlib, hash_function)(message).digest()
asn1 = hash_asn1[hash_function]
signature = b2i(signature)
plain = i2b(key.encrypt(signature), size=1024)
try:
plain_hash = plain[plain.index(bytes(b'\x00'), 2) + 1:] # have ASN1 HASH
except:
return False
if plain[:2] == bytes(b'\x00\x01') and plain_hash == asn1 + hash_msg:
return True
return False
def md5(data, initial_state=None, padding=None):
"""Compute MD5
Args:
data(string)
initial_state(list of ints)
padding(string/None): if None, padding will be computed
Returns:
digest(string)
"""
if initial_state is None:
initial_state = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]
if not padding:
data = add_md_padding(data, endian='little')
else:
data += padding
final_state = merkle_damgard(data, initial_state, compression_function_md5)
return bytes(b''.join(
[i2b(x, size=32, endian='little') for x in final_state]))
def sha1(data, initial_state=None, padding=None):
"""Compute SHA1
Args:
data(string)
initial_state(list of ints)
padding(string/None): if None, padding will be computed
Returns:
digest(string)
"""
if initial_state is None:
initial_state = [
0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0
]
if not padding:
data = add_md_padding(data, endian='big')
else:
data += padding
final_state = merkle_damgard(data, initial_state,
compression_function_sha1)
return bytes(b''.join([i2b(x, size=32) for x in final_state]))
def bleichenbacher_signature_forgery(key,
garbage='suffix',
hash_function='sha1'):
"""Bleichenbacher's signature forgery based on bug in verify implementation
Args:
key(RSAKey): with small e and at least one plaintext
garbage(string): middle: 00 01 ff garbage 00 ASN.1 HASH
suffix: 00 01 ff 00 ASN.1 HASH garbage
hash_function(string)
Returns:
dict: forged signatures, signatures[no] == signature(key.texts[no]['plain'])
update key texts
"""
hash_asn1 = {
'md5':
bytes(
b'\x30\x20\x30\x0c\x06\x08\x2a\x86\x48\x86\xf7\x0d\x02\x05\x05\x00\x04\x10'
),
'sha1':
bytes(b'\x30\x21\x30\x09\x06\x05\x2b\x0e\x03\x02\x1a\x05\x00\x04\x14'),
'sha256':
bytes(
b'\x30\x31\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01\x05\x00\x04\x20'
),
'sha384':
bytes(
b'\x30\x41\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x02\x05\x00\x04\x30'
),
'sha512':
bytes(
b'\x30\x51\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x03\x05\x00\x04\x40'
)
}
if garbage not in ['suffix', 'middle']:
log.critical_error("Bad garbage position, must be suffix or middle")
if hash_function not in list(hash_asn1.keys()):
log.critical_error(
"Hash function {} not implemented".format(hash_function))
if key.e > 3:
log.debug("May not work, because e > 3")
signatures = {}
if garbage == 'suffix':
for text_no in range(len(key.texts)):
if 'plain' in key.texts[text_no] and 'cipher' not in key.texts[
text_no]:
log.info("Forge for plaintext no {} ({})".format(
text_no, key.texts[text_no]['plain']))
hash_callable = getattr(hashlib, hash_function)(i2b(
key.texts[text_no]
['plain'])).digest() # hack to call hashlib.hash_function
plaintext_prefix = bytes(b'\x00\x01\xff\x00') + hash_asn1[
hash_function] + hash_callable
plaintext = plaintext_prefix + bytes(
b'\x00' * (key.size // 8 - len(plaintext_prefix)))
plaintext = b2i(plaintext)
for round_error in range(-5, 5):
signature, _ = gmpy2.iroot(plaintext, key.e)
signature = int(signature + round_error)
test_prefix = i2b(gmpy2.powmod(signature, key.e, key.n),
size=key.size)[:len(plaintext_prefix)]
if test_prefix == plaintext_prefix:
log.info("Got signature: {}".format(signature))
log.debug("signature**e % n == {}".format(
i2h(gmpy2.powmod(signature, key.e, key.n),
size=key.size)))
key.texts[text_no]['cipher'] = signature
signatures[text_no] = signature
break
else:
log.error(
"Something wrong, can't compute correct signature")
return signatures
elif garbage == 'middle':
for text_no in range(len(key.texts)):
if 'plain' in key.texts[text_no] and 'cipher' not in key.texts[
text_no]:
log.info("Forge for plaintext no {} ({})".format(
text_no, key.texts[text_no]['plain']))
hash_callable = getattr(hashlib, hash_function)(i2b(
key.texts[text_no]
['plain'])).digest() # hack to call hashlib.hash_function
plaintext_suffix = bytes(
b'\x00') + hash_asn1[hash_function] + hash_callable
if b2i(plaintext_suffix) & 1 != 1:
log.error(
"Plaintext suffix is even, can't compute signature")
continue
# compute suffix
signature_suffix = 0b1
for b in range(len(plaintext_suffix) * 8):
if (signature_suffix**
3) & (1 << b) != b2i(plaintext_suffix) & (1 << b):
signature_suffix |= 1 << b
signature_suffix = i2b(
signature_suffix)[-len(plaintext_suffix):]
# compute prefix
while True:
plaintext_prefix = bytes(b'\x00\x01\xff') + random_bytes(
key.size // 8 - 3)
signature_prefix, _ = gmpy2.iroot(b2i(plaintext_prefix),
key.e)
signature_prefix = i2b(
int(signature_prefix),
size=key.size)[:-len(signature_suffix)]
signature = b2i(signature_prefix + signature_suffix)
test_plaintext = i2b(gmpy2.powmod(signature, key.e, key.n),
size=key.size)
if bytes(b'\x00'
) not in test_plaintext[2:-len(plaintext_suffix)]:
if test_plaintext[:3] == plaintext_prefix[:3] and test_plaintext[
-len(plaintext_suffix):] == plaintext_suffix:
log.info("Got signature: {}".format(signature))
key.texts[text_no]['cipher'] = signature
signatures[text_no] = signature
break
else:
log.error("Something wrong, signature={},"
" signature**{}%{} is {}".format(
signature, key.e, key.n,
[(test_plaintext)]))
break
return signatures
def sign(message, key):
# message = add_rsa_signature_padding(message, size=key.size, hash_function='sha1')
message = b2i(message)
signature = pow(message, key.d, key.n)
return i2b(signature)
def decrypt(ciphertext, key):
ciphertext = b2i(ciphertext)
plaintext = pow(ciphertext, key.d, key.n)
return i2b(plaintext)
def encrypt(plaintext, key):
plaintext = b2i(plaintext)
ciphertext = pow(plaintext, key.e, key.n)
return i2b(ciphertext)
#!/usr/bin/env python
from CryptoAttacks.PublicKey import rsa
from CryptoAttacks.Utils import i2b
from gmpy2 import iroot
with open('../flag_enc.txt', 'rb') as f:
flag = f.read()
flag = int.from_bytes(flag, 'big')
key = rsa.RSAKey.import_key('../key.pem')
f = flag
for i in range(0, 300):
x = iroot(f, key.e)
if x[1]:
print(i, i2b(int(x[0])))
break
f += key.n