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# Copyright (C) 2007 by the Free Software Foundation, Inc.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
# USA.
"""Password hashing and verification schemes.
Represents passwords using RFC 2307 syntax.
"""
import os
import re
import sha
import hmac
from array import array
from base64 import urlsafe_b64decode as decode
from base64 import urlsafe_b64encode as encode
SALT_LENGTH = 20 # bytes
ITERATIONS = 2000
class PasswordScheme(object):
@staticmethod
def make_secret(password):
"""Return the hashed password"""
raise NotImplementedError
@staticmethod
def check_response(challenge, response):
"""Return True if response matches challenge.
It is expected that the scheme specifier prefix is already stripped
from the response string.
"""
raise NotImplementedError
class NoPasswordScheme(PasswordScheme):
@staticmethod
def make_secret(password):
return '{NONE}'
@staticmethod
def check_response(challenge, response):
return False
class ClearTextPasswordScheme(PasswordScheme):
@staticmethod
def make_secret(password):
return '{CLEARTEXT}' + password
@staticmethod
def check_response(challenge, response):
return challenge == response
class SHAPasswordScheme(PasswordScheme):
@staticmethod
def make_secret(password):
h = sha.new(password)
return '{SHA}' + encode(h.digest())
@staticmethod
def check_response(challenge, response):
h = sha.new(response)
return challenge == encode(h.digest())
class SSHAPasswordScheme(PasswordScheme):
@staticmethod
def make_secret(password):
salt = os.urandom(SALT_LENGTH)
h = sha.new(password)
h.update(salt)
return '{SSHA}' + encode(h.digest() + salt)
@staticmethod
def check_response(challenge, response):
# Get the salt from the challenge
challenge_bytes = decode(challenge)
digest = challenge_bytes[:20]
salt = challenge_bytes[20:]
h = sha.new(response)
h.update(salt)
return digest == h.digest()
# Given by Bob Fleck
class PBKDF2PasswordScheme(PasswordScheme):
@staticmethod
def _pbkdf2(password, salt, iterations):
"""From RFC2898 sec. 5.2. Simplified to handle only 20 byte output
case. Output of 20 bytes means always exactly one block to handle,
and a constant block counter appended to the salt in the initial hmac
update.
"""
h = hmac.new(password, None, sha)
prf = h.copy()
prf.update(salt + '\x00\x00\x00\x01')
T = U = array('l', prf.digest())
while iterations:
prf = h.copy()
prf.update(U.tostring())
U = array('l', prf.digest())
T = array('l', (t ^ u for t, u in zip(T, U)))
iterations -= 1
return T.tostring()
@staticmethod
def make_secret(password):
"""From RFC2898 sec. 5.2. Simplified to handle only 20 byte output
case. Output of 20 bytes means always exactly one block to handle,
and a constant block counter appended to the salt in the initial hmac
update.
"""
salt = os.urandom(SALT_LENGTH)
digest = PBKDF2PasswordScheme._pbkdf2(password, salt, ITERATIONS)
derived_key = encode(digest + salt)
return '{PBKDF2 SHA %d}' % ITERATIONS + derived_key
@staticmethod
def check_response(challenge, response, prf, iterations):
# Decode the challenge to get the number of iterations and salt
# XXX we don't support anything but sha prf
if prf.lower() <> 'sha':
return False
try:
iterations = int(iterations)
except (ValueError, TypeError):
return False
challenge_bytes = decode(challenge)
digest = challenge_bytes[:20]
salt = challenge_bytes[20:]
key = PBKDF2PasswordScheme._pbkdf2(response, salt, iterations)
return digest == key
SCHEMES = {
'none' : NoPasswordScheme,
'cleartext' : ClearTextPasswordScheme,
'sha' : SHAPasswordScheme,
'ssha' : SSHAPasswordScheme,
'pbkdf2' : PBKDF2PasswordScheme,
}
def make_secret(password, scheme):
scheme_class = SCHEMES.get(scheme.lower(), NoPasswordScheme)
return scheme_class.make_secret(password)
def check_response(challenge, response):
mo = re.match(r'{(?P<scheme>[^}]+?)}(?P<rest>.*)',
challenge, re.IGNORECASE)
if not mo:
return False
scheme, rest = mo.group('scheme', 'rest')
scheme_parts = scheme.split()
scheme_class = SCHEMES.get(scheme_parts[0].lower(), NoPasswordScheme)
return scheme_class.check_response(rest, response, *scheme_parts[1:])
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