# -*- coding: utf-8 -*-
#
#  Cipher/mode_cfb.py : CFB mode
#
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# 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.
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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
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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"""
Counter Feedback (CFB) mode.
"""

__all__ = ['CfbMode']

from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib, VoidPointer,
                                  create_string_buffer, get_raw_buffer,
                                  SmartPointer, c_size_t, expect_byte_string)

from Cryptodome.Random import get_random_bytes

raw_cfb_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._raw_cfb","""
                    int CFB_start_operation(void *cipher,
                                            const uint8_t iv[],
                                            size_t iv_len,
                                            size_t segment_len, /* In bytes */
                                            void **pResult);
                    int CFB_encrypt(void *cfbState,
                                    const uint8_t *in,
                                    uint8_t *out,
                                    size_t data_len);
                    int CFB_decrypt(void *cfbState,
                                    const uint8_t *in,
                                    uint8_t *out,
                                    size_t data_len);
                    int CFB_stop_operation(void *state);"""
                    )


class CfbMode(object):
    """*Cipher FeedBack (CFB)*.

    This mode is similar to CFB, but it transforms
    the underlying block cipher into a stream cipher.

    Plaintext and ciphertext are processed in *segments*
    of **s** bits. The mode is therefore sometimes
    labelled **s**-bit CFB.

    An Initialization Vector (*IV*) is required.

    See `NIST SP800-38A`_ , Section 6.3.

    .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf

    :undocumented: __init__
    """

    def __init__(self, block_cipher, iv, segment_size):
        """Create a new block cipher, configured in CFB mode.

        :Parameters:
          block_cipher : C pointer
            A smart pointer to the low-level block cipher instance.

          iv : byte string
            The initialization vector to use for encryption or decryption.
            It is as long as the cipher block.

            **The IV must be unpredictable**. Ideally it is picked randomly.

            Reusing the *IV* for encryptions performed with the same key
            compromises confidentiality.

          segment_size : integer
            The number of bytes the plaintext and ciphertext are segmented in.
        """

        expect_byte_string(iv)
        self._state = VoidPointer()
        result = raw_cfb_lib.CFB_start_operation(block_cipher.get(),
                                                 iv,
                                                 c_size_t(len(iv)),
                                                 c_size_t(segment_size),
                                                 self._state.address_of())
        if result:
            raise ValueError("Error %d while instatiating the CFB mode" % result)

        # Ensure that object disposal of this Python object will (eventually)
        # free the memory allocated by the raw library for the cipher mode
        self._state = SmartPointer(self._state.get(),
                                   raw_cfb_lib.CFB_stop_operation)

        # Memory allocated for the underlying block cipher is now owed
        # by the cipher mode
        block_cipher.release()

        self.block_size = len(iv)
        """The block size of the underlying cipher, in bytes."""

        self.iv = iv
        """The Initialization Vector originally used to create the object.
        The value does not change."""

        self.IV = iv
        """Alias for `iv`"""

        self._next = [ self.encrypt, self.decrypt ]

    def encrypt(self, plaintext):
        """Encrypt data with the key and the parameters set at initialization.

        A cipher object is stateful: once you have encrypted a message
        you cannot encrypt (or decrypt) another message using the same
        object.

        The data to encrypt can be broken up in two or
        more pieces and `encrypt` can be called multiple times.

        That is, the statement:

            >>> c.encrypt(a) + c.encrypt(b)

        is equivalent to:

             >>> c.encrypt(a+b)

        This function does not add any padding to the plaintext.

        :Parameters:
          plaintext : byte string
            The piece of data to encrypt.
            It can be of any length.
        :Return:
            the encrypted data, as a byte string.
            It is as long as *plaintext*.
        """

        if self.encrypt not in self._next:
            raise TypeError("encrypt() cannot be called after decrypt()")
        self._next = [ self.encrypt ]

        expect_byte_string(plaintext)
        ciphertext = create_string_buffer(len(plaintext))
        result = raw_cfb_lib.CFB_encrypt(self._state.get(),
                                         plaintext,
                                         ciphertext,
                                         c_size_t(len(plaintext)))
        if result:
            raise ValueError("Error %d while encrypting in CFB mode" % result)
        return get_raw_buffer(ciphertext)

    def decrypt(self, ciphertext):
        """Decrypt data with the key and the parameters set at initialization.

        A cipher object is stateful: once you have decrypted a message
        you cannot decrypt (or encrypt) another message with the same
        object.

        The data to decrypt can be broken up in two or
        more pieces and `decrypt` can be called multiple times.

        That is, the statement:

            >>> c.decrypt(a) + c.decrypt(b)

        is equivalent to:

             >>> c.decrypt(a+b)

        This function does not remove any padding from the plaintext.

        :Parameters:
          ciphertext : byte string
            The piece of data to decrypt.
            It can be of any length.

        :Return: the decrypted data (byte string).
        """

        if self.decrypt not in self._next:
            raise TypeError("decrypt() cannot be called after encrypt()")
        self._next = [ self.decrypt ]

        expect_byte_string(ciphertext)
        plaintext = create_string_buffer(len(ciphertext))
        result = raw_cfb_lib.CFB_decrypt(self._state.get(),
                                         ciphertext,
                                         plaintext,
                                         c_size_t(len(ciphertext)))
        if result:
            raise ValueError("Error %d while decrypting in CFB mode" % result)
        return get_raw_buffer(plaintext)


def _create_cfb_cipher(factory, **kwargs):
    """Instantiate a cipher object that performs CFB encryption/decryption.

    :Parameters:
      factory : module
        The underlying block cipher, a module from ``Cryptodome.Cipher``.

    :Keywords:
      iv : byte string
        The IV to use for CFB.

      IV : byte string
        Alias for ``iv``.

      segment_size : integer
        The number of bit the plaintext and ciphertext are segmented in.
        If not present, the default is 8.

    Any other keyword will be passed to the underlying block cipher.
    See the relevant documentation for details (at least ``key`` will need
    to be present).
    """

    cipher_state = factory._create_base_cipher(kwargs)

    iv = kwargs.pop("IV", None)
    IV = kwargs.pop("iv", None)

    if (None, None) == (iv, IV):
        iv = get_random_bytes(factory.block_size)
    if iv is not None:
        if IV is not None:
            raise TypeError("You must either use 'iv' or 'IV', not both")
    else:
        iv = IV

    segment_size_bytes, rem = divmod(kwargs.pop("segment_size", 8), 8)
    if segment_size_bytes == 0 or rem != 0:
        raise ValueError("'segment_size' must be positive and multiple of 8 bits")

    if kwargs:
        raise TypeError("Unknown parameters for CFB: %s" % str(kwargs))
    return CfbMode(cipher_state, iv, segment_size_bytes)
