def hmac_sha1(key, message):
"""
Creates an HMAC using SHA-1.
Args:
key: The HMAC key.
message: The message to generate the MAC for.
Returns:
The HMAC for the message under the given key
"""
# If the key is longer than the blocksize,
# then truncate it by hashing it
if (len(key) > 64):
key = sha1(key).digest()
# If the key is shorter than blocksize,
# pad with 0s
if (len(key) < 64):
key = key + (b'\x00' * (64 - len(key)))
o_pad = c2.xorstrs(key, b'\x5c' * 64)
i_pad = c2.xorstrs(key, b'\x36' * 64)
i_msg = i_pad + message
o_msg = o_pad + sha1(i_msg).digest()
return sha1(o_msg).digest()
def mac_sha1(message):
"""
Creates a message authentication code using SHA-1.
Args:
message: The message to create a code for.
Returns:
The MAC generated from the message by using SHA-1.
"""
return sha1(key + message).digest()
def forge_message(message, attack):
"""
Forge's a message with the associated MAC for a SHA-1 MAC
Args:
message: The untainted message
attack: The message to inject using length extension
Returns:
The forged message, tag pair for a SHA-1 length extension attack.
"""
new_regs = get_state(message)
glue_pad = glue_padding((b'\x00' * 16) + message)
forged_message = glue_pad[16:] + attack
forged_tag = sha1(attack, n_l=len(forged_message) + 16,
n_h=new_regs).digest()
return forged_message, forged_tag
def test_glue_padding(self):
self.assertEqual(sha1(b'abc').message, glue_padding(b'abc'))