ndnkdf.py

#
# Copyright (c) 2012, NORDUnet A/S
# All rights reserved.
#
#   Redistribution and use in source and binary forms, with or
#   without modification, are permitted provided that the following
#   conditions are met:
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#     1. Redistributions of source code must retain the above copyright
#        notice, this list of conditions and the following disclaimer.
#     2. 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.
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#        contributors may 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 HOLDER 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
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#
# Author : Fredrik Thulin <fredrik@thulin.net>
#

import os
import ctypes
import ctypes.util

class NDNKDF_Error(Exception):
    pass

class NDNKDF_LibraryError(NDNKDF_Error):
    pass

class NDNKDF():

    _DIGEST_SIZE=64

    """
    NORDUnet Key Derivation Function

    Really just a version of PBKDF2-HMAC-SHA512 using libnettle for speed.
    """

    def __init__(self, path=None):
        if path is None:
            path = os.environ.get('NDNKDF_PATH')
        if path is not None:
            self.name = os.path.join(path, 'libnettle.so')
        else:
            self.name = ctypes.util.find_library('nettle')
        self.nettle = ctypes.cdll.LoadLibrary(self.name)
        # check for the functions we use - the PBKDF2 function was added 2012-09-12
        # (appeared in Nettle version 2.6, SO version 4.4).
        if not hasattr(self.nettle, 'nettle_hmac_sha512_update'):
            raise NDNKDF_LibraryError('Nettle library missing function nettle_hmac_sha512_update()')
        if not hasattr(self.nettle, 'nettle_hmac_sha512_digest'):
            raise NDNKDF_LibraryError('Nettle library missing function nettle_hmac_sha512_digest()')
        if not hasattr(self.nettle, 'nettle_pbkdf2'):
            raise NDNKDF_LibraryError('Nettle library missing function nettle_pbkdf2()')

    def pbkdf2_hmac_sha512(self, key, iterations, salt):
        """
        Invoke nettle PBKDF2 using HMAC-SHA-512 on key, iterations and salt.
        """
        buf = ctypes.create_string_buffer('', size = self._DIGEST_SIZE)
        # sha512ctx is a C struct consisting of three sha512_ctx. I calculate them to be
        # 148 bytes each, but let's just fake it with an opaque buffer of 1024 bytes.
        sha512ctx = ctypes.create_string_buffer('', size = 1024)
        self.nettle.nettle_hmac_sha512_set_key(ctypes.byref(sha512ctx), len(key), key)
        self.nettle.nettle_pbkdf2( \
            ctypes.byref(sha512ctx), \
                self.nettle.nettle_hmac_sha512_update, \
                self.nettle.nettle_hmac_sha512_digest, \
                self._DIGEST_SIZE, int(iterations), \
                len(salt), salt, \
                self._DIGEST_SIZE, ctypes.byref(buf) \
                )
        return buf.raw