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✏️ Editing: cSHAKE128.py

# ===================================================================
#
# Copyright (c) 2021, Legrandin <helderijs@gmail.com>
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#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
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# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in
#    the documentation and/or other materials provided with the
#    distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# ===================================================================

from Crypto.Util.py3compat import bchr

from Crypto.Util._raw_api import (VoidPointer, SmartPointer,
                                  create_string_buffer,
                                  get_raw_buffer, c_size_t,
                                  c_uint8_ptr, c_ubyte)

from Crypto.Util.number import long_to_bytes

from Crypto.Hash.keccak import _raw_keccak_lib

def _left_encode(x):
    """Left encode function as defined in NIST SP 800-185"""

assert (x < (1 << 2040) and x >= 0)

# Get number of bytes needed to represent this integer.
    num = 1 if x == 0 else (x.bit_length() + 7) // 8

return bchr(num) + long_to_bytes(x)

def _right_encode(x):
    """Right encode function as defined in NIST SP 800-185"""

assert (x < (1 << 2040) and x >= 0)

# Get number of bytes needed to represent this integer.
    num = 1 if x == 0 else (x.bit_length() + 7) // 8

return long_to_bytes(x) + bchr(num)

def _encode_str(x):
    """Encode string function as defined in NIST SP 800-185"""

bitlen = len(x) * 8
    if bitlen >= (1 << 2040):
        raise ValueError("String too large to encode in cSHAKE")

return _left_encode(bitlen) + x

def _bytepad(x, length):
    """Zero pad byte string as defined in NIST SP 800-185"""

to_pad = _left_encode(length) + x

# Note: this implementation works with byte aligned strings,
    # hence no additional bit padding is needed at this point.
    npad = (length - len(to_pad) % length) % length

return to_pad + b'\x00' * npad

class cSHAKE_XOF(object):
    """A cSHAKE hash object.
    Do not instantiate directly.
    Use the :func:`new` function.
    """

def __init__(self, data, custom, capacity, function):
        state = VoidPointer()

if custom or function:
            prefix_unpad = _encode_str(function) + _encode_str(custom)
            prefix = _bytepad(prefix_unpad, (1600 - capacity)//8)
            self._padding = 0x04
        else:
            prefix = None
            self._padding = 0x1F  # for SHAKE

result = _raw_keccak_lib.keccak_init(state.address_of(),
                                             c_size_t(capacity//8),
                                             c_ubyte(24))
        if result:
            raise ValueError("Error %d while instantiating cSHAKE"
                             % result)
        self._state = SmartPointer(state.get(),
                                   _raw_keccak_lib.keccak_destroy)
        self._is_squeezing = False

if prefix:
            self.update(prefix)

if data:
            self.update(data)

def update(self, data):
        """Continue hashing of a message by consuming the next chunk of data.

Args:
            data (byte string/byte array/memoryview): The next chunk of the message being hashed.
        """

if self._is_squeezing:
            raise TypeError("You cannot call 'update' after the first 'read'")

result = _raw_keccak_lib.keccak_absorb(self._state.get(),
                                               c_uint8_ptr(data),
                                               c_size_t(len(data)))
        if result:
            raise ValueError("Error %d while updating %s state"
                             % (result, self.name))
        return self

def read(self, length):
        """
        Compute the next piece of XOF output.

.. note::
            You cannot use :meth:`update` anymore after the first call to
            :meth:`read`.

Args:
            length (integer): the amount of bytes this method must return

:return: the next piece of XOF output (of the given length)
        :rtype: byte string
        """

self._is_squeezing = True
        bfr = create_string_buffer(length)
        result = _raw_keccak_lib.keccak_squeeze(self._state.get(),
                                                bfr,
                                                c_size_t(length),
                                                c_ubyte(self._padding))
        if result:
            raise ValueError("Error %d while extracting from %s"
                             % (result, self.name))

return get_raw_buffer(bfr)

def _new(data, custom, function):
    # Use Keccak[256]
    return cSHAKE_XOF(data, custom, 256, function)

def new(data=None, custom=None):
    """Return a fresh instance of a cSHAKE128 object.

Args:
       data (bytes/bytearray/memoryview):
        Optional.
        The very first chunk of the message to hash.
        It is equivalent to an early call to :meth:`update`.
       custom (bytes):
        Optional.
        A customization bytestring (``S`` in SP 800-185).

:Return: A :class:`cSHAKE_XOF` object
    """

# Use Keccak[256]
    return cSHAKE_XOF(data, custom, 256, b'')

MR SKB