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"""SHA-256 cryptographic hash algorithm.

SHA-256 belongs to the SHA-2_ family of cryptographic hashes.
It produces the 256 bit digest of a message.

    >>> from Crypto.Hash import SHA256
    >>>
    >>> h = SHA256.new()
    >>> h.update(b'Hello')
    >>> print h.hexdigest()

*SHA* stands for Secure Hash Algorithm.

.. _SHA-2: http://csrc.nist.gov/publications/fips/fips180-2/fips180-4.pdf
"""

from Crypto.Util.py3compat import *

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

_raw_sha256_lib = load_pycryptodome_raw_lib("Crypto.Hash._SHA256",
                        """
                        int SHA256_init(void **shaState);
                        int SHA256_destroy(void *shaState);
                        int SHA256_update(void *hs,
                                          const uint8_t *buf,
                                          size_t len);
                        int SHA256_digest(const void *shaState,
                                          uint8_t digest[32]);
                        int SHA256_copy(const void *src, void *dst);
                        """)

class SHA256Hash(object):
    """Class that implements a SHA-256 hash
    """

    #: The size of the resulting hash in bytes.
    digest_size = 32
    #: The internal block size of the hash algorithm in bytes.
    block_size = 64
    #: ASN.1 Object ID
    oid = "2.16.840.1.101.3.4.2.1"

    def __init__(self, data=None):
        state = VoidPointer()
        result = _raw_sha256_lib.SHA256_init(state.address_of())
        if result:
            raise ValueError("Error %d while instantiating SHA256"
                             % result)
        self._state = SmartPointer(state.get(),
                                   _raw_sha256_lib.SHA256_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.
        """

        expect_byte_string(data)
        result = _raw_sha256_lib.SHA256_update(self._state.get(),
                                               data,
                                               c_size_t(len(data)))
        if result:
            raise ValueError("Error %d while instantiating SHA256"
                             % result)

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

        This method does not change the state of the hash object.
        You can continue updating the object after calling this function.

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

        bfr = create_string_buffer(self.digest_size)
        result = _raw_sha256_lib.SHA256_digest(self._state.get(),
                                               bfr)
        if result:
            raise ValueError("Error %d while instantiating SHA256"
                             % result)

        return get_raw_buffer(bfr)

    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 copy(self):
        """Return a copy ("clone") of the hash object.

        The copy will have the same internal state as the original hash
        object.
        This can be used to efficiently compute the digests of strings that
        share a common initial substring.

        :Return: A hash object of the same type
        """

        clone = SHA256Hash()
        result = _raw_sha256_lib.SHA256_copy(self._state.get(),
                                             clone._state.get())
        if result:
            raise ValueError("Error %d while copying SHA256" % result)
        return clone

    def new(self, data=None):
        return SHA256Hash(data)

def new(data=None):
    """Return a fresh instance of the hash object.

    :Parameters:
       data : byte string
        The very first chunk of the message to hash.
        It is equivalent to an early call to `SHA256Hash.update()`.
        Optional.

    :Return: A `SHA256Hash` object
    """
    return SHA256Hash().new(data)

#: The size of the resulting hash in bytes.
digest_size = SHA256Hash.digest_size

#: The internal block size of the hash algorithm in bytes.
block_size = SHA256Hash.block_size

