pbkdf2.py

# -*- coding: utf-8 -*-
"""
    Copyright (c) 2011 by Armin Ronacher.

    Some rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

        * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

        * Redistributions in binary form must reproduce the above
        copyright notice, this list of conditions and the following
        disclaimer in the documentation and/or other materials provided
        with the distribution.

        * The names of the contributors may not be used to endorse or
        promote products derived from this software without specific
        prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    pbkdf2
    ~~~~~~

    This module implements pbkdf2 for Python.  It also has some basic
    tests that ensure that it works.  The implementation is straightforward
    and uses stdlib only stuff and can be easily be copy/pasted into
    your favourite application.

    Use this as replacement for bcrypt that does not need a c implementation
    of a modified blowfish crypto algo.

    Example usage:

    >>> pbkdf2_hex('what i want to hash', 'the random salt')
    'fa7cc8a2b0a932f8e6ea42f9787e9d36e592e0c222ada6a9'

    How to use this:

    1.  Use a constant time string compare function to compare the stored hash
        with the one you're generating::

            def safe_str_cmp(a, b):
                if len(a) != len(b):
                    return False
                rv = 0
                for x, y in izip(a, b):
                    rv |= ord(x) ^ ord(y)
                return rv == 0

    2.  Use `os.urandom` to generate a proper salt of at least 8 byte.
        Use a unique salt per hashed password.

    3.  Store ``algorithm$salt:costfactor$hash`` in the database so that
        you can upgrade later easily to a different algorithm if you need
        one.  For instance ``PBKDF2-256$thesalt:10000$deadbeef...``.


    :copyright: (c) Copyright 2011 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""

import hmac
import hashlib
from struct import Struct
from operator import xor
from itertools import izip, starmap


_pack_int = Struct('>I').pack


def pbkdf2_hex(data, salt, iterations=1000, keylen=24, hashfunc=None):
    """Like :func:`pbkdf2_bin` but returns a hex encoded string."""
    return pbkdf2_bin(data, salt, iterations, keylen, hashfunc).encode('hex')


def pbkdf2_bin(data, salt, iterations=1000, keylen=24, hashfunc=None):
    """Returns a binary digest for the PBKDF2 hash algorithm of `data`
    with the given `salt`.  It iterates `iterations` time and produces a
    key of `keylen` bytes.  By default SHA-1 is used as hash function,
    a different hashlib `hashfunc` can be provided.
    """
    hashfunc = hashfunc or hashlib.sha1
    mac = hmac.new(data, None, hashfunc)
    def _pseudorandom(x, mac=mac):
        h = mac.copy()
        h.update(x)
        return map(ord, h.digest())
    buf = []
    for block in xrange(1, -(-keylen // mac.digest_size) + 1):
        rv = u = _pseudorandom(salt + _pack_int(block))
        for i in xrange(iterations - 1):
            u = _pseudorandom(''.join(map(chr, u)))
            rv = starmap(xor, izip(rv, u))
        buf.extend(rv)
    return ''.join(map(chr, buf))[:keylen]


def test():
    failed = []
    def check(data, salt, iterations, keylen, expected):
        rv = pbkdf2_hex(data, salt, iterations, keylen)
        if rv != expected:
            print 'Test failed:'
            print '  Expected:   %s' % expected
            print '  Got:        %s' % rv
            print '  Parameters:'
            print '    data=%s' % data
            print '    salt=%s' % salt
            print '    iterations=%d' % iterations
            print
            failed.append(1)

    # From RFC 6070
    check('password', 'salt', 1, 20,
          '0c60c80f961f0e71f3a9b524af6012062fe037a6')
    check('password', 'salt', 2, 20,
          'ea6c014dc72d6f8ccd1ed92ace1d41f0d8de8957')
    check('password', 'salt', 4096, 20,
          '4b007901b765489abead49d926f721d065a429c1')
    check('passwordPASSWORDpassword', 'saltSALTsaltSALTsaltSALTsaltSALTsalt',
          4096, 25, '3d2eec4fe41c849b80c8d83662c0e44a8b291a964cf2f07038')
    check('pass\x00word', 'sa\x00lt', 4096, 16,
          '56fa6aa75548099dcc37d7f03425e0c3')
    # This one is from the RFC but it just takes for ages
    ##check('password', 'salt', 16777216, 20,
    ##      'eefe3d61cd4da4e4e9945b3d6ba2158c2634e984')

    # From Crypt-PBKDF2
    check('password', 'ATHENA.MIT.EDUraeburn', 1, 16,
          'cdedb5281bb2f801565a1122b2563515')
    check('password', 'ATHENA.MIT.EDUraeburn', 1, 32,
          'cdedb5281bb2f801565a1122b25635150ad1f7a04bb9f3a333ecc0e2e1f70837')
    check('password', 'ATHENA.MIT.EDUraeburn', 2, 16,
          '01dbee7f4a9e243e988b62c73cda935d')
    check('password', 'ATHENA.MIT.EDUraeburn', 2, 32,
          '01dbee7f4a9e243e988b62c73cda935da05378b93244ec8f48a99e61ad799d86')
    check('password', 'ATHENA.MIT.EDUraeburn', 1200, 32,
          '5c08eb61fdf71e4e4ec3cf6ba1f5512ba7e52ddbc5e5142f708a31e2e62b1e13')
    check('X' * 64, 'pass phrase equals block size', 1200, 32,
          '139c30c0966bc32ba55fdbf212530ac9c5ec59f1a452f5cc9ad940fea0598ed1')
    check('X' * 65, 'pass phrase exceeds block size', 1200, 32,
          '9ccad6d468770cd51b10e6a68721be611a8b4d282601db3b36be9246915ec82a')

    raise SystemExit(bool(failed))


if __name__ == '__main__':
    test()