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CAST.py

# -*- coding: utf-8 -*-
#
#  Cipher/CAST.py : CAST
#
# ===================================================================
# The contents of this file are dedicated to the public domain.  To
# 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.
#
# 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
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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"""
Module's constants for the modes of operation supported with CAST:

:var MODE_ECB: :ref:`Electronic Code Book (ECB) <ecb_mode>`
:var MODE_CBC: :ref:`Cipher-Block Chaining (CBC) <cbc_mode>`
:var MODE_CFB: :ref:`Cipher FeedBack (CFB) <cfb_mode>`
:var MODE_OFB: :ref:`Output FeedBack (OFB) <ofb_mode>`
:var MODE_CTR: :ref:`CounTer Mode (CTR) <ctr_mode>`
:var MODE_OPENPGP:  :ref:`OpenPGP Mode <openpgp_mode>`
:var MODE_EAX: :ref:`EAX Mode <eax_mode>`
"""

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, c_uint8_ptr)

_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")

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(c_uint8_ptr(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 cipher

:param key:
        The secret key to use in the symmetric cipher.
        Its length can vary from 5 to 16 bytes.
    :type key: bytes, bytearray, memoryview

:param mode:
        The chaining mode to use for encryption or decryption.
    :type mode: One of the supported ``MODE_*`` constants

:Keyword Arguments:
        *   **iv** (*bytes*, *bytearray*, *memoryview*) --
            (Only applicable for ``MODE_CBC``, ``MODE_CFB``, ``MODE_OFB``,
            and ``MODE_OPENPGP`` modes).

The initialization vector to use for encryption or decryption.

For ``MODE_CBC``, ``MODE_CFB``, and ``MODE_OFB`` it must be 8 bytes long.

For ``MODE_OPENPGP`` mode only,
            it 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).

If not provided, a random byte string is generated (you must then
            read its value with the :attr:`iv` attribute).

*   **nonce** (*bytes*, *bytearray*, *memoryview*) --
            (Only applicable for ``MODE_EAX`` and ``MODE_CTR``).

A value that must never be reused for any other encryption done
            with this key.

For ``MODE_EAX`` there are no
            restrictions on its length (recommended: **16** bytes).

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

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

*   **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.

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

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

:Return: a CAST object, of the applicable mode.
    """

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

MODE_ECB = 1
MODE_CBC = 2
MODE_CFB = 3
MODE_OFB = 5
MODE_CTR = 6
MODE_OPENPGP = 7
MODE_EAX = 9

# Size of a data block (in bytes)
block_size = 8
# Size of a key (in bytes)
key_size = range(5, 16 + 1)

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