1
  "   	ˆl–Ðz¾”Jj"TÊ‚Æ^¸)‹FÿÅƒ}—YÄÃ $    	# -*- coding: utf-8 -*-
#
#  Cipher/PKCS1_OAEP.py : PKCS#1 OAEP
#
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# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# ===================================================================

"""RSA encryption protocol according to PKCS#1 OAEP

See RFC3447__ or the `original RSA Labs specification`__ .

This scheme is more properly called ``RSAES-OAEP``.

As an example, a sender may encrypt a message in this way:

        >>> from Crypto.Cipher import PKCS1_OAEP
        >>> from Crypto.PublicKey import RSA
        >>>
        >>> message = 'To be encrypted'
        >>> key = RSA.importKey(open('pubkey.der').read())
        >>> cipher = PKCS1_OAEP.new(key)
        >>> ciphertext = cipher.encrypt(message)

At the receiver side, decryption can be done using the private part of
the RSA key:

        >>> key = RSA.importKey(open('privkey.der').read())
        >>> cipher = PKCS1_OAP.new(key)
        >>> message = cipher.decrypt(ciphertext)

:undocumented: __revision__, __package__

.. __: http://www.ietf.org/rfc/rfc3447.txt
.. __: http://www.rsa.com/rsalabs/node.asp?id=2125.
"""

from __future__ import nested_scopes

__revision__ = "$Id$"
__all__ = [ 'new', 'PKCS1OAEP_Cipher' ]

import Crypto.Signature.PKCS1_PSS
import Crypto.Hash.SHA

from Crypto.Util.py3compat import *
import Crypto.Util.number
from   Crypto.Util.number import ceil_div
from   Crypto.Util.strxor import strxor

class PKCS1OAEP_Cipher:
    """This cipher can perform PKCS#1 v1.5 OAEP encryption or decryption."""

    def __init__(self, key, hashAlgo, mgfunc, label):
        """Initialize this PKCS#1 OAEP cipher object.
        
        :Parameters:
         key : an RSA key object
          If a private half is given, both encryption and decryption are possible.
          If a public half is given, only encryption is possible.
         hashAlgo : hash object
                The hash function to use. This can be a module under `Crypto.Hash`
                or an existing hash object created from any of such modules. If not specified,
                `Crypto.Hash.SHA` (that is, SHA-1) is used.
         mgfunc : callable
                A mask generation function that accepts two parameters: a string to
                use as seed, and the lenth of the mask to generate, in bytes.
                If not specified, the standard MGF1 is used (a safe choice).
         label : string
                A label to apply to this particular encryption. If not specified,
                an empty string is used. Specifying a label does not improve
                security.
 
        :attention: Modify the mask generation function only if you know what you are doing.
                    Sender and receiver must use the same one.
        """
        self._key = key

        if hashAlgo:
            self._hashObj = hashAlgo
        else:
            self._hashObj = Crypto.Hash.SHA

        if mgfunc:
            self._mgf = mgfunc
        else:
            self._mgf = lambda x,y: Crypto.Signature.PKCS1_PSS.MGF1(x,y,self._hashObj)

        self._label = label

    def can_encrypt(self):
        """Return True/1 if this cipher object can be used for encryption."""
        return self._key.can_encrypt()

    def