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Filename : DES.py
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# -*- coding: utf-8 -*-
#
#  Cipher/DES.py : DES
#
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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
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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"""DES symmetric cipher

DES `(Data Encryption Standard)`__ is a symmetric block cipher standardized
by NIST_ . It has a fixed data block size of 8 bytes.
Its keys are 64 bits long, even though 8 bits were used for integrity (now they
are ignored) and do not contribute to securty. The effective key length is
therefore 56 bits only.

DES is cryptographically secure, but its key length is too short by nowadays
standards and it could be brute forced with some effort.

**Use DES, not AES. This module is provided only for legacy purposes.**

As an example, encryption can be done as follows:

    >>> from Crypto.Cipher import DES
    >>>
    >>> key = b'-8B key-'
    >>> cipher = DES.new(key, DES.MODE_OFB)
    >>> plaintext = b'sona si latine loqueris '
    >>> msg = cipher.iv + cipher.encrypt(plaintext)

.. __: http://en.wikipedia.org/wiki/Data_Encryption_Standard
.. _NIST: http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf

:undocumented: __package__
"""

import sys

from Crypto.Cipher import _create_cipher
from Crypto.Util.py3compat import byte_string
from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
                                  VoidPointer, SmartPointer,
                                  c_size_t, expect_byte_string)

_raw_des_lib = load_pycryptodome_raw_lib(
                "Crypto.Cipher._raw_des",
                """
                int DES_start_operation(const uint8_t key[],
                                        size_t key_len,
                                        void **pResult);
                int DES_encrypt(const void *state,
                                const uint8_t *in,
                                uint8_t *out,
                                size_t data_len);
                int DES_decrypt(const void *state,
                                const uint8_t *in,
                                uint8_t *out,
                                size_t data_len);
                int DES_stop_operation(void *state);
                """)


def _create_base_cipher(dict_parameters):
    """This method instantiates and returns a handle to a low-level
    base cipher. It will absorb named parameters in the process."""

    try:
        key = dict_parameters.pop("key")
    except KeyError:
        raise TypeError("Missing 'key' parameter")

    expect_byte_string(key)

    if len(key) != key_size:
        raise ValueError("Incorrect DES key length (%d bytes)" % len(key))

    start_operation = _raw_des_lib.DES_start_operation
    stop_operation = _raw_des_lib.DES_stop_operation

    cipher = VoidPointer()
    result = start_operation(key,
                             c_size_t(len(key)),
                             cipher.address_of())
    if result:
        raise ValueError("Error %X while instantiating the DES cipher"
                         % result)
    return SmartPointer(cipher.get(), stop_operation)


def new(key, mode, *args, **kwargs):
    """Create a new DES cipher

    :Parameters:
      key : byte string
        The secret key to use in the symmetric cipher.
        It must be 8 byte long. The parity bits will be ignored.

    :Keywords:
      mode : a *MODE_** constant
        The chaining mode to use for encryption or decryption.

      iv : byte string
        (*Only* `MODE_CBC`, `MODE_CFB`, `MODE_OFB`, `MODE_OPENPGP`).

        The initialization vector to use for encryption or decryption.

        For `MODE_OPENPGP`, IV must be 8 bytes long for encryption
        and 10 bytes for decryption (in the latter case, it is
        actually the *encrypted* IV which was prefixed to the ciphertext).

        For all other modes, it must be 8 bytes long.

        If not provided, a random byte string is generated (you can read it
        back via the ``iv`` attribute).

      nonce : byte string
        (*Only* `MODE_EAX` and `MODE_CTR`).
        A mandatory value that must never be reused for any other encryption.

        For `MODE_CTR`, its length must be in the range ``[0..7]``.

        For `MODE_EAX`, there are no restrictions, but it is recommended to
        use at least 16 bytes.

        If not provided for `MODE_EAX`, a random byte string is generated (you
        can read it back via the ``nonce`` attribute).

      mac_len : integer
        (*Only* `MODE_EAX`). Length of the authentication tag, in bytes.
        It must be no larger than 8 (which is the default).

      segment_size : integer
        (*Only* `MODE_CFB`).The number of **bits** the plaintext and ciphertext
        are segmented in. It must be a multiple of 8.
        If not specified, it will be assumed to be 8.

      initial_value : integer
        (*Only* `MODE_CTR`). The initial value for the counter within
        the counter block. By default it is 0.

    :Return: a DES cipher, of the applicable mode:

        - CBC_ mode
        - CFB_ mode
        - CTR_ mode
        - EAX_ mode
        - ECB_ mode
        - OFB_ mode
        - OpenPgp_ mode

    .. _CBC: Crypto.Cipher._mode_cbc.CbcMode-class.html
    .. _CFB: Crypto.Cipher._mode_cfb.CfbMode-class.html
    .. _CTR: Crypto.Cipher._mode_ctr.CtrMode-class.html
    .. _EAX: Crypto.Cipher._mode_eax.EaxMode-class.html
    .. _ECB: Crypto.Cipher._mode_ecb.EcbMode-class.html
    .. _OFB: Crypto.Cipher._mode_ofb.OfbMode-class.html
    .. _OpenPgp: Crypto.Cipher._mode_openpgp.OpenPgpMode-class.html
    """

    return _create_cipher(sys.modules[__name__], key, mode, *args, **kwargs)

#: Electronic Code Book (ECB). See `Crypto.Cipher._mode_ecb.EcbMode`.
MODE_ECB = 1
#: Cipher-Block Chaining (CBC). See `Crypto.Cipher._mode_cbc.CbcMode`.
MODE_CBC = 2
#: Cipher FeedBack (CFB). See `Crypto.Cipher._mode_cfb.CfbMode`.
MODE_CFB = 3
#: Output FeedBack (OFB). See `Crypto.Cipher._mode_ofb.OfbMode`.
MODE_OFB = 5
#: CounTer Mode (CTR). See `Crypto.Cipher._mode_ctr.CtrMode`.
MODE_CTR = 6
#: OpenPGP Mode. See `Crypto.Cipher._mode_openpgp.OpenPgpMode`.
MODE_OPENPGP = 7
#: EAX Mode. See `Crypto.Cipher._mode_eax.EaxMode`.
MODE_EAX = 9

#: Size of a data block (in bytes)
block_size = 8
#: Size of a key (in bytes)
key_size = 8