def _decrypt_stealth(self, descriptor_cookie):
assert len(self._crypted_data) > 2 + self.CIPHER_IV_LEN, 'Size of encrypted data is too small'
assert self._crypted_data[0] == AuthType.Stealth
iv = self._crypted_data[1:1 + self.CIPHER_IV_LEN]
d = aes_ctr_decryptor(descriptor_cookie, iv)
data = self._crypted_data[1 + self.CIPHER_IV_LEN:]
return d.update(data)
def _decrypt_basic(self, descriptor_cookie):
assert self._crypted_data[0] == AuthType.Basic
block_count = self._crypted_data[1]
entries_len = block_count * self.REND_BASIC_AUTH_CLIENT_MULTIPLE * self.REND_BASIC_AUTH_CLIENT_ENTRY_LEN
assert len(self._crypted_data) > 2 + entries_len + self.CIPHER_IV_LEN, 'Size of crypted data too small'
iv = self._crypted_data[2 + entries_len:2 + entries_len + self.CIPHER_IV_LEN]
client_id = sha1(descriptor_cookie + iv)[:4]
session_key = self._get_session_key(self._crypted_data[2:2 + entries_len], descriptor_cookie, client_id)
d = aes_ctr_decryptor(session_key, iv)
data = self._crypted_data[2 + entries_len + self.CIPHER_IV_LEN:]
return d.update(data)
def _get_session_key(self, data, descriptor_cookie, client_id):
pos = 0
d = aes_ctr_decryptor(descriptor_cookie)
while pos < len(data):
if data[pos:pos + self.REND_BASIC_AUTH_CLIENT_ID_LEN] == client_id:
start_key_pos = pos + self.REND_BASIC_AUTH_CLIENT_ID_LEN
end_key_pos = start_key_pos + self.CIPHER_KEY_LEN
enc_session_key = data[start_key_pos:end_key_pos]
return aes_update(d, enc_session_key)
pos += self.REND_BASIC_AUTH_CLIENT_ENTRY_LEN
raise Exception('Session key for client {!r} not found'.format(client_id))
def __init__(self, data):
"""
Parse handshake data and create forward/backward digests.
When used in the ntor handshake, the first HASH_LEN bytes form the
forward digest Df; the next HASH_LEN form the backward digest Db; the
next KEY_LEN form Kf, the next KEY_LEN form Kb, and the final
DIGEST_LEN bytes are taken as a nonce to use in the place of KH in the
hidden service protocol. Excess bytes from K are discarded.
:type data: bytes
"""
(_fdig, _bdig, _ekey, _dkey) = struct.unpack('!20s20s16s16s', data)
self._forward_digest = sha1_stream(_fdig)
self._backward_digest = sha1_stream(_bdig)
self._forward_cipher = aes_ctr_encryptor(_ekey)
self._backward_cipher = aes_ctr_decryptor(_dkey)
