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Filename : SHA256.py
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# -*- coding: utf-8 -*-
#
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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/fips180-2.pdf
"""

_revision__ = "$Id$"

__all__ = ['new', 'digest_size', 'SHA256Hash' ]

from Crypto.Util.py3compat import *
from Crypto.Hash.hashalgo import HashAlgo

try:
    import hashlib
    hashFactory = hashlib.sha256

except ImportError:
    from Crypto.Hash import _SHA256
    hashFactory = _SHA256

class SHA256Hash(HashAlgo):
    """Class that implements a SHA-256 hash
    
    :undocumented: block_size
    """

    #: ASN.1 Object identifier (OID)::
    #:
    #:  id-sha256    OBJECT IDENTIFIER ::= {
    #: 	    joint-iso-itu-t(2) country(16) us(840) organization(1)
    #: 	     gov(101) csor(3) nistalgorithm(4) hashalgs(2) 1
    #:  }
    #:
    #: This value uniquely identifies the SHA-256 algorithm.
    oid = b('\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01')

    digest_size = 32
    block_size = 64

    def __init__(self, data=None):
        HashAlgo.__init__(self, hashFactory, data)

    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