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.. hazmat::
Message digests
===============
.. module:: cryptography.hazmat.primitives.hashes
.. class:: Hash(algorithm, backend)
A cryptographic hash function takes an arbitrary block of data and
calculates a fixed-size bit string (a digest), such that different data
results (with a high probability) in different digests.
This is an implementation of
:class:`~cryptography.hazmat.primitives.hashes.HashContext` meant to
be used with
:class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`
implementations to provide an incremental interface to calculating
various message digests.
.. doctest::
>>> from cryptography.hazmat.backends import default_backend
>>> from cryptography.hazmat.primitives import hashes
>>> digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
>>> digest.update(b"abc")
>>> digest.update(b"123")
>>> digest.finalize()
'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90'
If the backend doesn't support the requested ``algorithm`` an
:class:`~cryptography.exceptions.UnsupportedAlgorithm` exception will be
raised.
Keep in mind that attacks against cryptographic hashes only get stronger
with time, and that often algorithms that were once thought to be strong,
become broken. Because of this it's important to include a plan for
upgrading the hash algorithm you use over time. For more information, see
`Lifetimes of cryptographic hash functions`_.
:param algorithm: A
:class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`
provider such as those described in
:ref:`below <cryptographic-hash-algorithms>`.
:param backend: A
:class:`~cryptography.hazmat.backends.interfaces.HashBackend`
provider.
:raises cryptography.exceptions.UnsupportedAlgorithm: This is raised if the
provided ``backend`` does not implement
:class:`~cryptography.hazmat.backends.interfaces.HashBackend`
|
