# -*- coding: utf-8 -*-
#
#  Cipher/CAST.py : CAST
#
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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,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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"""CAST-128 symmetric cipher

CAST-128_ (or CAST5) is a symmetric block cipher specified in RFC2144_.

It has a fixed data block size of 8 bytes. Its key can vary in length
from 40 to 128 bits.

CAST is deemed to be cryptographically secure, but its usage is not widespread.
Keys of sufficient length should be used to prevent brute force attacks
(128 bits are recommended).

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

As an example, encryption can be done as follows:

    >>> from Crypto.Cipher import CAST
    >>>
    >>> key = b'Sixteen byte key'
    >>> cipher = CAST.new(key, CAST.MODE_OPENPGP)
    >>> plaintext = b'sona si latine loqueris '
    >>> msg = cipher.encrypt(plaintext)
    >>>
    ...
    >>> eiv = msg[:CAST.block_size+2]
    >>> ciphertext = msg[CAST.block_size+2:]
    >>> cipher = CAST.new(key, CAST.MODE_OPENPGP, eiv)
    >>> print cipher.decrypt(ciphertext)

.. _CAST-128: http://en.wikipedia.org/wiki/CAST-128
.. _RFC2144: http://tools.ietf.org/html/rfc2144

: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_cast_lib = load_pycryptodome_raw_lib(
                    "Crypto.Cipher._raw_cast",
                    """
                    int CAST_start_operation(const uint8_t key[],
                                             size_t key_len,
                                             void **pResult);
                    int CAST_encrypt(const void *state,
                                     const uint8_t *in,
                                     uint8_t *out,
                                     size_t data_len);
                    int CAST_decrypt(const void *state,
                                     const uint8_t *in,
                                     uint8_t *out,
                                     size_t data_len);
                    int CAST_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) not in key_size:
        raise ValueError("Incorrect CAST key length (%d bytes)" % len(key))

    start_operation = _raw_cast_lib.CAST_start_operation
    stop_operation = _raw_cast_lib.CAST_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 CAST cipher"
                         % result)

    return SmartPointer(cipher.get(), stop_operation)


def new(key, mode, *args, **kwargs):
    """Create a new CAST-128 cipher

    :Parameters:
      key : byte string
        The secret key to use in the symmetric cipher.
        Its length may vary from 5 to 16 bytes.
        The recommended length is 16 bytes.

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

    :Keywords:
      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 will be 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 16 byte string will be
        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 CAST cipher object, 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 = xrange(5, 16 + 1)
