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from __future__ import unicode_literals
from random import SystemRandom as random
from six import integer_types, PY3
from .utils import int_from_hex, int_to_bytes, hex_from, value_encode, b64_from
from .constants import PRIME_1024, PRIME_1024_GEN, HASH_SHA_1
from .exceptions import SRPException
class SRPContext(object):
"""
* The SRP Authentication and Key Exchange System
https://tools.ietf.org/html/rfc2945
* Using the Secure Remote Password (SRP) Protocol for TLS Authentication
https://tools.ietf.org/html/rfc5054
"""
def __init__(
self, username, password=None, prime=None, generator=None, hash_func=None, multiplier=None,
bits_random=1024, bits_salt=64):
"""
:param str|unicode username: User name
:param str|unicode password: User _password
:param str|unicode|None prime: Prime hex string . Default: PRIME_1024
:param str|unicode|None generator: Generator hex string. Default: PRIME_1024_GEN
:param str|unicode hash_func: Function to calculate hash. Default: HASH_SHA_1
:param str|unicode multiplier: Multiplier hex string. If not given will be calculated
automatically using _prime and _gen.
:param int bits_random: Random value bits. Default: 1024
:param int bits_salt: Salt value bits. Default: 64
"""
self._hash_func = hash_func or HASH_SHA_1 # H
self._user = username # I
self._password = password # p
self._gen = int_from_hex(generator or PRIME_1024_GEN) # g
self._prime = int_from_hex(prime or PRIME_1024) # N
self._mult = ( # k = H(N | PAD(g))
int_from_hex(multiplier) if multiplier else self.hash(self._prime, self.pad(self._gen)))
self._bits_salt = bits_salt
self._bits_random = bits_random
@property
def generator(self):
return hex_from(self._gen)
@property
def generator_b64(self):
return b64_from(self._gen)
@property
def prime(self):
return hex_from(self._prime)
@property
def prime_b64(self):
return b64_from(self._prime)
def pad(self, val):
"""
:param val:
:rtype: bytes
"""
padding = len(int_to_bytes(self._prime))
padded = int_to_bytes(val).rjust(padding, b'\x00')
return padded
def hash(self, *args, **kwargs):
"""
:param args:
:param kwargs:
joiner - string to join values (args)
as_bytes - bool to return hash bytes instead of default int
:rtype: int|bytes
"""
joiner = kwargs.get('joiner', '').encode('utf-8')
as_bytes = kwargs.get('as_bytes', False)
def conv(arg):
if isinstance(arg, integer_types):
arg = int_to_bytes(arg)
if PY3:
if isinstance(arg, str):
arg = arg.encode('utf-8')
return arg
return str(arg)
digest = joiner.join(map(conv, args))
hash_obj = self._hash_func(digest)
if as_bytes:
return hash_obj.digest()
return int_from_hex(hash_obj.hexdigest())
def generate_random(self, bits_len=None):
"""Generates a random value.
:param int bits_len:
:rtype: int
"""
bits_len = bits_len or self._bits_random
return random().getrandbits(bits_len)
def generate_salt(self):
"""s = random
:rtype: int
"""
return self.generate_random(self._bits_salt)
def get_common_secret(self, server_public, client_public):
"""u = H(PAD(A) | PAD(B))
:param int server_public:
:param int client_public:
:rtype: int
"""
return self.hash(self.pad(client_public), self.pad(server_public))
def get_client_premaster_secret(self, password_hash, server_public, client_private, common_secret):
"""S = (B - (k * g^x)) ^ (a + (u * x)) % N
:param int server_public:
:param int password_hash:
:param int client_private:
:param int common_secret:
:rtype: int
"""
password_verifier = self.get_common_password_verifier(password_hash)
return pow(
(server_public - (self._mult * password_verifier)),
(client_private + (common_secret * password_hash)), self._prime)
def get_common_session_key(self, premaster_secret):
"""K = H(S)
:param int premaster_secret:
:rtype: bytes
"""
return self.hash(premaster_secret, as_bytes=True)
def get_server_premaster_secret(self, password_verifier, server_private, client_public, common_secret):
"""S = (A * v^u) ^ b % N
:param int password_verifier:
:param int server_private:
:param int client_public:
:param int common_secret:
:rtype: int
"""
return pow((client_public * pow(password_verifier, common_secret, self._prime)), server_private, self._prime)
def generate_client_private(self):
"""a = random()
:rtype: int
"""
return self.generate_random()
def generate_server_private(self):
"""b = random()
:rtype: int
"""
return self.generate_random()
def get_client_public(self, client_private):
"""A = g^a % N
:param int client_private:
:rtype: int
"""
return pow(self._gen, client_private, self._prime)
def get_server_public(self, password_verifier, server_private):
"""B = (k*v + g^b) % N
:param int password_verifier:
:param int server_private:
:rtype: int
"""
return ((self._mult * password_verifier) + pow(self._gen, server_private, self._prime)) % self._prime
def get_common_password_hash(self, salt):
"""x = H(s | H(I | ":" | P))
:param int salt:
:rtype: int
"""
password = self._password
if password is None:
raise SRPException('User password should be in context for this scenario.')
return self.hash(salt, self.hash(self._user, password, joiner=':', as_bytes=True))
def get_common_password_verifier(self, password_hash):
"""v = g^x % N
:param int password_hash:
:rtype: int
"""
return pow(self._gen, password_hash, self._prime)
def get_common_session_key_proof(self, session_key, salt, server_public, client_public):
"""M = H(H(N) XOR H(g) | H(U) | s | A | B | K)
:param bytes session_key:
:param int salt:
:param int server_public:
:param int client_public:
:rtype: bytes
"""
h = self.hash
prove = h(
h(self._prime) ^ h(self._gen),
h(self._user),
salt,
client_public,
server_public,
session_key,
as_bytes=True
)
return prove
def get_common_session_key_proof_hash(self, session_key, session_key_proof, client_public):
"""H(A | M | K)
:param bytes session_key:
:param bytes session_key_proof:
:param int client_public:
:rtype: bytes
"""
return self.hash(client_public, session_key_proof, session_key, as_bytes=True)
def get_user_data_triplet(self, base64=False):
"""( <_user>, <_password verifier>, <salt> )
:param base64:
:rtype: tuple
"""
salt = self.generate_salt()
verifier = self.get_common_password_verifier(self.get_common_password_hash(salt))
verifier = value_encode(verifier, base64)
salt = value_encode(salt, base64)
return self._user, verifier, salt
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