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Filename : TupleHash128.py
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# Copyright (c) 2021, Legrandin <helderijs@gmail.com>
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from Crypto.Util.py3compat import bord, is_bytes, tobytes

from . import cSHAKE128
from .cSHAKE128 import _encode_str, _right_encode


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

    def __init__(self, custom, cshake, digest_size):

        self.digest_size = digest_size

        self._cshake = cshake._new(b'', custom, b'TupleHash')
        self._digest = None

    def update(self, data):
        """Authenticate the next byte string in the tuple.

        Args:
            data (bytes/bytearray/memoryview): The next byte string.
        """

        if self._digest is not None:
            raise TypeError("You cannot call 'update' after 'digest' or 'hexdigest'")

        if not is_bytes(data):
            raise TypeError("You can only call 'update' on bytes")

        self._cshake.update(_encode_str(tobytes(data)))

        return self

    def digest(self):
        """Return the **binary** (non-printable) digest of the tuple of byte strings.

        :return: The hash digest. Binary form.
        :rtype: byte string
        """

        if self._digest is None:
            self._cshake.update(_right_encode(self.digest_size * 8))
            self._digest = self._cshake.read(self.digest_size)

        return self._digest

    def hexdigest(self):
        """Return the **printable** digest of the tuple of byte strings.

        :return: The hash digest. Hexadecimal encoded.
        :rtype: string
        """

        return "".join(["%02x" % bord(x) for x in tuple(self.digest())])

    def new(self, **kwargs):
        """Return a new instance of a TupleHash object.
        See :func:`new`.
        """

        if "digest_bytes" not in kwargs and "digest_bits" not in kwargs:
            kwargs["digest_bytes"] = self.digest_size

        return new(**kwargs)


def new(**kwargs):
    """Create a new TupleHash128 object.

    Args:
       digest_bytes (integer):
        Optional. The size of the digest, in bytes.
        Default is 64. Minimum is 8.
       digest_bits (integer):
        Optional and alternative to ``digest_bytes``.
        The size of the digest, in bits (and in steps of 8).
        Default is 512. Minimum is 64.
       custom (bytes):
        Optional.
        A customization bytestring (``S`` in SP 800-185).

    :Return: A :class:`TupleHash` object
    """

    digest_bytes = kwargs.pop("digest_bytes", None)
    digest_bits = kwargs.pop("digest_bits", None)
    if None not in (digest_bytes, digest_bits):
        raise TypeError("Only one digest parameter must be provided")
    if (None, None) == (digest_bytes, digest_bits):
        digest_bytes = 64
    if digest_bytes is not None:
        if digest_bytes < 8:
            raise ValueError("'digest_bytes' must be at least 8")
    else:
        if digest_bits < 64 or digest_bits % 8:
            raise ValueError("'digest_bytes' must be at least 64 "
                             "in steps of 8")
        digest_bytes = digest_bits // 8

    custom = kwargs.pop("custom", b'')

    if kwargs:
        raise TypeError("Unknown parameters: " + str(kwargs))

    return TupleHash(custom, cSHAKE128, digest_bytes)