pycryptodome/lib/Crypto/Cipher/DES.py

# -*- coding: utf-8 -*-
#
#  Cipher/DES.py : DES
#
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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.

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

DES should not be used for new designs. Use `AES`.

As an example, encryption can be done as follows:

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

        It is ignored for `MODE_ECB` and `MODE_CTR`.

        For `MODE_OPENPGP`, IV must be `block_size` bytes long for encryption
        and `block_size` +2 bytes for decryption (in the latter case, it is
        actually the *encrypted* IV which was prefixed to the ciphertext).
        It is mandatory.

        For all other modes, it must be 8 bytes long.
      nonce : byte string
        (*Only* `MODE_EAX`).
        A mandatory value that must never be reused for any other encryption.
        There are no restrictions on its length, but it is recommended to
        use at least 16 bytes.
      counter : callable
        (*Only* `MODE_CTR`). A stateful function that returns the next
        *counter block*, which is a byte string of `block_size` bytes.
        For better performance, use `Crypto.Util.Counter`.
      mac_len : integer
        (*Only* `MODE_EAX`). Length of the MAC, 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 0 or not specified, it will be assumed
        to be 8.

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

    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