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Filename : SHA3_256.py
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# -*- coding: utf-8 -*-
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# non-exclusive license to exercise all rights associated with the
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"""SHA-3/256 cryptographic hash algorithm.

SHA-3/256 belongs to the SHA-3 family of cryptographic hashes, as specified
in `FIPS 202`__.

The hash function produces the 256 bit digest of a message.

    >>> from Crypto.Hash import SHA3_256
    >>>
    >>> h_obj = SHA3_256.new()
    >>> h_obj.update(b'Some data')
    >>> print h_obj.hexdigest()

.. __: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf
"""

from Crypto.Util.py3compat import bord

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

from Crypto.Hash.keccak import _raw_keccak_lib

class SHA3_256_Hash(object):
    """Class that implements a SHA-3/256 hash
    """

    #: The size of the resulting hash in bytes.
    digest_size = 32

    #: ASN.1 Object ID
    oid = "2.16.840.1.101.3.4.2.8"

    def __init__(self, data, update_after_digest):
        self._update_after_digest = update_after_digest
        self._digest_done = False

        state = VoidPointer()
        result = _raw_keccak_lib.keccak_init(state.address_of(),
                                             c_size_t(self.digest_size * 2),
                                             0x06)
        if result:
            raise ValueError("Error %d while instantiating SHA-3/256"
                             % result)
        self._state = SmartPointer(state.get(),
                                   _raw_keccak_lib.keccak_destroy)
        if data:
            self.update(data)

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

        Repeated calls are equivalent to a single call with the concatenation
        of all the arguments. In other words:

           >>> m.update(a); m.update(b)

        is equivalent to:

           >>> m.update(a+b)

        :Parameters:
          data : byte string
            The next chunk of the message being hashed.
        """

        if self._digest_done and not self._update_after_digest:
            raise TypeError("You can only call 'digest' or 'hexdigest' on this object")

        expect_byte_string(data)
        result = _raw_keccak_lib.keccak_absorb(self._state.get(),
                                               data,
                                               c_size_t(len(data)))
        if result:
            raise ValueError("Error %d while updating SHA-3/256"
                             % result)
        return self

    def digest(self):
        """Return the **binary** (non-printable) digest of the message that has been hashed so far.

        You cannot update the hash anymore after the first call to ``digest``
        (or ``hexdigest``).

        :Return: A byte string of `digest_size` bytes. It may contain non-ASCII
         characters, including null bytes.
        """

        self._digest_done = True

        bfr = create_string_buffer(self.digest_size)
        result = _raw_keccak_lib.keccak_digest(self._state.get(),
                                               bfr,
                                               c_size_t(self.digest_size))
        if result:
            raise ValueError("Error %d while instantiating SHA-3/256"
                             % result)

        self._digest_value = get_raw_buffer(bfr)
        return self._digest_value

    def hexdigest(self):
        """Return the **printable** digest of the message that has been hashed so far.

        This method does not change the state of the hash object.

        :Return: A string of 2* `digest_size` characters. It contains only
         hexadecimal ASCII digits.
        """

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

    def new(self):
        return type(self)(None, self._update_after_digest)


def new(*args, **kwargs):
    """Return a fresh instance of the hash object.

    :Keywords:
      data : byte string
        Optional. The very first chunk of the message to hash.
        It is equivalent to an early call to ``update()``.
      update_after_digest : boolean
        Optional. By default, a hash object cannot be updated anymore after
        the digest is computed. When this flag is ``True``, such check
        is no longer enforced.

    :Return: A `SHA3_256_Hash` object
    """

    data = kwargs.pop("data", None)
    update_after_digest = kwargs.pop("update_after_digest", False)
    if len(args) == 1:
        if data:
            raise ValueError("Initial data for hash specified twice")
        data = args[0]

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

    return SHA3_256_Hash(data, update_after_digest)

#: The size of the resulting hash in bytes.
digest_size = SHA3_256_Hash.digest_size