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#!/usr/bin/env python
"""
Make an OpenID association request against an endpoint and print the results.
Usage: associate.py [options] <endpoint>
associate.py -h | --help
Options:
-h, --help show this help message and exit
-a, --assoc-type=ASSOC_TYPE set custom association type [default: HMAC-SHA256]
-s, --session-type=SES_TYPE set custom session type [default: DH-SHA256]
--generate-modulus generate another modulus (may take some time)
--generator=GENERATOR set custom generator value [default: 2]
-d, --debug print debug information
"""
from __future__ import unicode_literals
import base64
import binascii
import codecs
import logging
import sys
import requests
import six
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.asymmetric.dh import DHParameterNumbers, DHPublicNumbers, generate_parameters
from docopt import docopt
# This script is intentionaly and completely independent on the openid library.
# That should prevent any unwanted changes in association establishing.
DEFAULT_DH_MODULUS = int(
'155172898181473697471232257763715539915724801966915404479707795314057629378541917580651227423698188993727816152646'
'631438561595825688188889951272158842675419950341258706556549803580104870537681476726513255747040765857479291291572'
'334510643245094715007229621094194349783925984760375594985848253359305585439638443'
)
DEFAULT_DH_GENERATOR = 2
OPENID2_NS = 'http://specs.openid.net/auth/2.0'
########################################################################################################################
# Utilities copied from the openid library
def int_to_bytes(value):
"""Convert integer -> bytes."""
hex_value = '{:x}'.format(value)
if len(hex_value) % 2:
hex_value = '0' + hex_value
array = bytearray.fromhex(hex_value)
# First bit must be zero. If it isn't, the bytes must be prepended by zero byte.
# See http://openid.net/specs/openid-authentication-2_0.html#btwoc for details.
if array[0] > 127:
array = bytearray([0]) + array
return six.binary_type(array)
def int_to_base64(number):
"""Convert int -> base64."""
number_bytes = int_to_bytes(number)
return binascii.b2a_base64(number_bytes)[:-1].decode('utf-8')
def base64_to_int(value):
binary_value = binascii.a2b_base64(value)
return int(codecs.encode(binary_value, 'hex'), 16)
def strxor(x, y):
if len(x) != len(y):
raise ValueError('Inputs to strxor must have the same length')
if six.PY2:
return b"".join(chr(ord(a) ^ ord(b)) for a, b in zip(x, y))
else:
assert six.PY3
return bytes((a ^ b) for a, b in zip(x, y))
def parse_kv_response(response):
"""Parse the key-value response."""
decoded_data = {}
for line in response.text.splitlines():
line = line.strip()
if not line:
continue
pair = line.split(':', 1)
if not len(pair) == 2:
logging.warn("Not a key-value line: %s", line)
continue
key, value = pair
decoded_data[key.strip()] = value.strip()
return decoded_data
########################################################################################################################
# The association code itself
def parse_association_response(response):
"""Parse the association response."""
association_data = parse_kv_response(response)
if association_data.get('ns') != OPENID2_NS:
raise ValueError("Response is not an OpenID 2.0 response")
for key in ('assoc_type', 'session_type', 'assoc_handle', 'expires_in', 'dh_server_public', 'enc_mac_key'):
if key not in association_data:
raise ValueError("Required key {} is not in response.".format(key))
return association_data
def establish_association(endpoint, assoc_type, session_type, generator, generate_modulus):
"""Actually establish the association."""
generator = int(generator)
if generate_modulus:
parameters = generate_parameters(generator=generator, key_size=2048, backend=default_backend())
parameter_numbers = parameters.parameter_numbers()
else:
parameter_numbers = DHParameterNumbers(DEFAULT_DH_MODULUS, generator)
parameters = parameter_numbers.parameters(default_backend())
private_key = parameters.generate_private_key()
public_key = int_to_base64(private_key.public_key().public_numbers().y)
logging.debug("Private key: %s", private_key.private_numbers().x)
logging.debug("Public key: %s", private_key.public_key().public_numbers().y)
data = {'openid.ns': OPENID2_NS,
'openid.mode': 'associate',
'openid.assoc_type': assoc_type,
'openid.session_type': session_type,
'openid.dh_consumer_public': public_key}
if parameter_numbers != DHParameterNumbers(DEFAULT_DH_MODULUS, DEFAULT_DH_GENERATOR):
data['openid.dh_modulus'] = int_to_base64(parameter_numbers.p)
data['openid.dh_gen'] = int_to_base64(parameter_numbers.g)
logging.info("Query arguments: %s", data)
response = requests.post(endpoint, data=data)
if response.status_code != 200:
if response.status_code == 400:
# Is it an error response?
error_data = parse_kv_response(response)
if error_data.get('mode') == 'error':
# It's an error response
raise ValueError("Server responded with error: {}".format(error_data.get('error')))
raise ValueError("Response returned incorrect status code: {}".format(response.status_code))
association_data = parse_association_response(response)
logging.debug("Association data: %s", association_data)
if association_data['assoc_type'] != assoc_type:
raise ValueError(
"Unexpected assoc_type returned {}, expected {}".format(association_data['assoc_type'], assoc_type))
if association_data['session_type'] != session_type:
raise ValueError(
"Unexpected session_type returned {}, expected {}".format(association_data['session_type'], session_type))
server_public_key = base64_to_int(association_data['dh_server_public'])
shared_secret = private_key.exchange(
DHPublicNumbers(server_public_key, parameter_numbers).public_key(default_backend()))
# Not an ordinary DH secret is used here.
# According to http://openid.net/specs/openid-authentication-2_0.html#rfc.section.8.2.3, the first bit of
# the DH secret must be zero. If it isn't, the bytes must be prepended by zero byte before they're hashed.
shared_secret = bytearray(shared_secret)
if shared_secret[0] > 127:
shared_secret = bytearray([0]) + shared_secret
shared_secret = bytes(shared_secret)
logging.debug("DH shared secret: %s", base64.b64encode(shared_secret))
algorithm = getattr(hashes, assoc_type[5:])
digest = hashes.Hash(algorithm(), backend=default_backend())
digest.update(shared_secret)
hashed_dh_shared = digest.finalize()
mac_key = strxor(base64.b64decode(association_data['enc_mac_key']), hashed_dh_shared)
return {'assoc_type': association_data['assoc_type'],
'session_type': association_data['session_type'],
'assoc_handle': association_data['assoc_handle'],
'expires_in': association_data['expires_in'],
'mac_key': base64.b64encode(mac_key).decode('utf-8')}
def main():
"""Main script."""
options = docopt(__doc__)
# Set up logging
if options['--debug']:
level = logging.DEBUG
else:
level = logging.WARNING
logging.basicConfig(level=level, format='%(asctime)s %(levelname)s:%(funcName)s: %(message)s')
try:
association = establish_association(options['<endpoint>'], options['--assoc-type'], options['--session-type'],
options['--generator'], options['--generate-modulus'])
except ValueError as error:
sys.stderr.write("Association failed.\n{}\n".format(error))
sys.exit(1)
for key, value in association.items():
sys.stdout.write('{}: {}\n'.format(key, value))
if __name__ == '__main__':
main()
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