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 #Ź    # -*- coding: utf-8 -*-
#
#  Cipher/PKCS1-v1_5.py : PKCS#1 v1.5
#
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# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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"""RSA encryption protocol according to PKCS#1 v1.5

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

This scheme is more properly called ``RSAES-PKCS1-v1_5``.

**If you are designing a new protocol, consider using the more robust PKCS#1 OAEP.**

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

        >>> from Crypto.Cipher import PKCS1_v1_5
        >>> from Crypto.PublicKey import RSA
        >>> from Crypto.Hash import SHA
        >>>
        >>> message = 'To be encrypted'
        >>> h = SHA.new(message)
        >>>
        >>> key = RSA.importKey(open('pubkey.der').read())
        >>> cipher = PKCS1_v1_5.new(key)
        >>> ciphertext = cipher.encrypt(message+h.digest())

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

        >>> From Crypto.Hash import SHA
        >>> from Crypto import Random
        >>>
        >>> key = RSA.importKey(open('privkey.der').read())
        >>>
        >>> dsize = SHA.digest_size
        >>> sentinel = Random.new().read(15+dsize)      # Let's assume that average data length is 15
        >>>
        >>> cipher = PKCS1_v1_5.new(key)
        >>> message = cipher.decrypt(ciphertext, sentinel)
        >>>
        >>> digest = SHA.new(message[:-dsize]).digest()
        >>> if digest==message[-dsize:]:                # Note how we DO NOT look for the sentinel
        >>>     print "Encryption was correct."
        >>> else:
        >>>     print "Encryption was not correct."

:undocumented: __revision__, __package__

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

__revision__ = "$Id$"
__all__ = [ 'new', 'PKCS115_Cipher' ]

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

class PKCS115_Cipher:
    """This cipher can perform PKCS#1 v1.5 RSA encryption or decryption."""

    def __init__(self, key):
        """Initialize this PKCS#1 v1.5 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.
        """
        self._key = key

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

    def can_decrypt(self):
        """Return True if this cipher object can be used for decryption."""
        return self._key.can_decrypt()

    def encrypt(self, message):
        """Produce the PKCS#1 v1.5 encryption of a message.
    
        This function is named ``RSAES-PKCS1-V1_5-ENCRYPT``, and is specified in
        section 7.2.1 of RFC3447.
        For a complete example see `Crypto.Cipher.PKCS1_v1_5`.
    
        :Parameters:
         message : byte string
                The message to encrypt, also known as plaintext. It can be of
                variable length, but not longer than the RSA modulus (in bytes) minus 11.
    
        :Return: A byte string