#!/usr/bin/python
# -*- coding: ascii -*-
###########################################################################
# pbkdf2 - PKCS#5 v2.0 Password-Based Key Derivation
#
# Copyright (C) 2007-2011 Dwayne C. Litzenberger <dlitz@dlitz.net>
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#
# Country of origin: Canada
#
###########################################################################
# Sample PBKDF2 usage:
#   from Crypto.Cipher import AES
#   from pbkdf2 import PBKDF2
#   import os
#
#   salt = os.urandom(8)    # 64-bit salt
#   key = PBKDF2("This passphrase is a secret.", salt).read(32) # 256-bit key
#   iv = os.urandom(16)     # 128-bit IV
#   cipher = AES.new(key, AES.MODE_CBC, iv)
#     ...
#
# Sample crypt() usage:
#   from pbkdf2 import crypt
#   pwhash = crypt("secret")
#   alleged_pw = raw_input("Enter password: ")
#   if pwhash == crypt(alleged_pw, pwhash):
#       print "Password good"
#   else:
#       print "Invalid password"
#
###########################################################################

__version__ = "1.3"
__all__ = ['PBKDF2', 'crypt']

from struct import pack
from random import randint
import string
import sys

try:
    # Use PyCrypto (if available).
    from Crypto.Hash import HMAC, SHA as SHA1
except ImportError:
    # PyCrypto not available.  Use the Python standard library.
    import hmac as HMAC
    try:
        from hashlib import sha1 as SHA1
    except ImportError:
        # hashlib not available.  Use the old sha module.
        import sha as SHA1


# Added (jamalex) to use M2Crypto's PBKDF2 for crypt, if available, for efficiency
# TODO(jamalex): add tests, as per discussion at:
# https://github.com/learningequality/ka-lite/pull/84
try:
    import M2Crypto.EVP
    def pbkdf2(word, salt, iterations):
        return M2Crypto.EVP.pbkdf2(word, str(salt), iterations, 24)
except:
    # if not available, just use the pure Python implementation
    def pbkdf2(word, salt, iterations):
        return PBKDF2(word, salt, iterations).read(24)

    
#
# Python 2.1 thru 3.2 compatibility
#

if sys.version_info[0] == 2:
    _0xffffffffL = long(1) << 32
    def isunicode(s):
        return isinstance(s, unicode)
    def isbytes(s):
        return isinstance(s, str)
    def isinteger(n):
        return isinstance(n, (int, long))
    def b(s):
        return s
    def binxor(a, b):
        return "".join([chr(ord(x) ^ ord(y)) for (x, y) in zip(a, b)])
    def b64encode(data, chars="+/"):
        tt = string.maketrans("+/", chars)
        return data.encode('base64').replace("\n", "").translate(tt)
    from binascii import b2a_hex
else:
    _0xffffffffL = 0xffffffff
    def isunicode(s):
        return isinstance(s, str)
    def isbytes(s):
        return isinstance(s, bytes)
    def isinteger(n):
        return isinstance(n, int)
    def callable(obj):
        return hasattr(obj, '__call__')
    def b(s):
       return s.encode("latin-1")
    def binxor(a, b):
        return bytes([x ^ y for (x, y) in zip(a, b)])
    from base64 import b64encode as _b64encode
    def b64encode(data, chars="+/"):
        if isunicode(chars):
            return _b64encode(data, chars.encode('utf-8')).decode('utf-8')
        else:
            return _b64encode(data, chars)
    from binascii import b2a_hex as _b2a_hex
    def b2a_hex(s):
        return _b2a_hex(s).decode('us-ascii')
    xrange = range

class PBKDF2(object):
    """PBKDF2.py : PKCS#5 v2.0 Password-Based Key Derivation

    This implementation takes a passphrase and a salt (and optionally an
    iteration count, a digest module, and a MAC module) and provides a
    file-like object from which an arbitrarily-sized key can be read.

    If the passphrase and/or salt are unicode objects, they are encoded as
    UTF-8 before they are processed.

    The idea behind PBKDF2 is to derive a cryptographic key from a
    passphrase and a salt.

    PBKDF2 may also be used as a strong salted password hash.  The
    'crypt' function is provided for that purpose.

    Remember: Keys generated using PBKDF2 are only as strong as the
    passphrases they are derived from.
    """

    def __init__(self, passphrase, salt, iterations=1000,
                 digestmodule=SHA1, macmodule=HMAC):
        self.__macmodule = macmodule
        self.__digestmodule = digestmodule
        self._setup(passphrase, salt, iterations, self._pseudorandom)

    def _pseudorandom(self, key, msg):
        """Pseudorandom function.  e.g. HMAC-SHA1"""
        return self.__macmodule.new(key=key, msg=msg,
            digestmod=self.__digestmodule).digest()

    def read(self, bytes):
        """Read the specified number of key bytes."""
        if self.closed:
            raise ValueError("file-like object is closed")

        size = len(self.__buf)
        blocks = [self.__buf]
        i = self.__blockNum
        while size < bytes:
            i += 1
            if i > _0xffffffffL or i < 1:
                # We could return "" here, but
                raise OverflowError("derived key too long")
            block = self.__f(i)
            blocks.append(block)
            size += len(block)
        buf = b("").join(blocks)
        retval = buf[:bytes]
        self.__buf = buf[bytes:]
        self.__blockNum = i
        return retval

    def __f(self, i):
        # i must fit within 32 bits
        assert 1 <= i <= _0xffffffffL
        U = self.__prf(self.__passphrase, self.__salt + pack("!L", i))
        result = U
        for j in xrange(2, 1+self.__iterations):
            U = self.__prf(self.__passphrase, U)
            result = binxor(result, U)
        return result

    def hexread(self, octets):
        """Read the specified number of octets. Return them as hexadecimal.

        Note that len(obj.hexread(n)) == 2*n.
        """
        return b2a_hex(self.read(octets))

    def _setup(self, passphrase, salt, iterations, prf):
        # Sanity checks:

        # passphrase and salt must be str or unicode (in the latter
        # case, we convert to UTF-8)
        if isunicode(passphrase):
            passphrase = passphrase.encode("UTF-8")
        elif not isbytes(passphrase):
            raise TypeError("passphrase must be str or unicode")
        if isunicode(salt):
            salt = salt.encode("UTF-8")
        elif not isbytes(salt):
            raise TypeError("salt must be str or unicode")

        # iterations must be an integer >= 1
        if not isinteger(iterations):
            raise TypeError("iterations must be an integer")
        if iterations < 1:
            raise ValueError("iterations must be at least 1")

        # prf must be callable
        if not callable(prf):
            raise TypeError("prf must be callable")

        self.__passphrase = passphrase
        self.__salt = salt
        self.__iterations = iterations
        self.__prf = prf
        self.__blockNum = 0
        self.__buf = b("")
        self.closed = False

    def close(self):
        """Close the stream."""
        if not self.closed:
            del self.__passphrase
            del self.__salt
            del self.__iterations
            del self.__prf
            del self.__blockNum
            del self.__buf
            self.closed = True

def crypt(word, salt=None, iterations=None):
    """PBKDF2-based unix crypt(3) replacement.

    The number of iterations specified in the salt overrides the 'iterations'
    parameter.

    The effective hash length is 192 bits.
    """

    # Generate a (pseudo-)random salt if the user hasn't provided one.
    if salt is None:
        salt = _makesalt()

    # salt must be a string or the us-ascii subset of unicode
    if isunicode(salt):
        salt = salt.encode('us-ascii').decode('us-ascii')
    elif isbytes(salt):
        salt = salt.decode('us-ascii')
    else:
        raise TypeError("salt must be a string")

    # word must be a string or unicode (in the latter case, we convert to UTF-8)
    if isunicode(word):
        word = word.encode("UTF-8")
    elif not isbytes(word):
        raise TypeError("word must be a string or unicode")

    # Try to extract the real salt and iteration count from the salt
    if salt.startswith("$p5k2$"):
        (iterations, salt, dummy) = salt.split("$")[2:5]
        if iterations == "":
            iterations = 400
        else:
            converted = int(iterations, 16)
            if iterations != "%x" % converted:  # lowercase hex, minimum digits
                raise ValueError("Invalid salt")
            iterations = converted
            if not (iterations >= 1):
                raise ValueError("Invalid salt")

    # Make sure the salt matches the allowed character set
    allowed = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789./"
    for ch in salt:
        if ch not in allowed:
            raise ValueError("Illegal character %r in salt" % (ch,))

    if iterations is None or iterations == 400:
        iterations = 400
        salt = "$p5k2$$" + salt
    else:
        salt = "$p5k2$%x$%s" % (iterations, salt)

    rawhash = pbkdf2(word, salt, iterations)

    return salt + "$" + b64encode(rawhash, "./")

# Add crypt as a static method of the PBKDF2 class
# This makes it easier to do "from PBKDF2 import PBKDF2" and still use
# crypt.
PBKDF2.crypt = staticmethod(crypt)

def _makesalt():
    """Return a 48-bit pseudorandom salt for crypt().

    This function is not suitable for generating cryptographic secrets.
    """
    binarysalt = b("").join([pack("@H", randint(0, 0xffff)) for i in range(3)])
    return b64encode(binarysalt, "./")

# vim:set ts=4 sw=4 sts=4 expandtab:
