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=============================================================
:class:`passlib.hash.grub_pbkdf2_sha512` - Grub's PBKDF2 Hash
=============================================================
.. index:: pbkdf2 hash; grub
.. currentmodule:: passlib.hash
This class provides an implementation of Grub's PBKDF2-HMAC-SHA512
password hash [#grub]_, as generated by the :command:`grub-mkpasswd-pbkdf2` command,
and may be found in Grub2 configuration files.
PBKDF2 is a key derivation function [#pbkdf2]_
that is ideally suited as the basis for a password hash, as it provides
variable length salts, variable number of rounds.
.. seealso::
* :ref:`password hash usage <password-hash-examples>` --
for examples of how to use this class via the common hash interface.
* :doc:`passlib.hash.pbkdf2_{digest} <passlib.hash.pbkdf2_digest>` --
for some other PBKDF2-based hashes.
Interface
=========
.. autoclass:: grub_pbkdf2_sha512()
Format & Algorithm
==================
A example hash (of ``password``) is ::
grub.pbkdf2.sha512.10000.4483972AD2C52E1F590B3E2260795FDA9CA0B07B
96FF492814CA9775F08C4B59CD1707F10B269E09B61B1E2D11729BCA8D62B7827
B25B093EC58C4C1EAC23137.DF4FCB5DD91340D6D31E33423E4210AD47C7A4DF9
FA16F401663BF288C20BF973530866178FE6D134256E4DBEFBD984B652332EED3
ACAED834FEA7B73CAE851D
All of this scheme's hashes have the format :samp:`grub.pbkdf2.sha512.{rounds}.{salt}.{checksum}`,
where :samp:`{rounds}` is the number of iteration stored in decimal,
:samp:`{salt}` is the salt string encoded using upper-case hexadecimal,
and :samp:`{checksum}` is the resulting 64-byte derived key, also
encoded in upper-case hexadecimal. It can be identified by the prefix ``grub.pdkdf2.sha512.``.
The algorithm used is the same as :class:`pbkdf2_sha1`: the password is encoded into UTF-8 if not already encoded,
and passed through :func:`~passlib.crypto.digest.pbkdf1`
along with the decoded salt, and the number of rounds.
The result is then encoded into hexadecimal.
..
Hash Translation
----------------
Note that despite encoding and format differences,
:class:`pbkdf2_sha512` and :class:`!grub_pbkdf2_sha512` share an identical algorithm,
and one can be converted to the other using the following code::
>>> from passlib.hash import pbkdf2_sha512, grub_pbkdf2_sha512
>>> # given a pbkdf2_sha512 hash...
>>> h = pbkdf2_sha512.hash("password")
>>> h
'$pbkdf2-sha512$6400$y6vYff3SihJiqumIrNXwGw$NobVwyUlVI52/Cvrguwli5fX6XgKHNUf7fWWS2VgoWEevaTCiZx4OCYhwGFwzUAuz/g1zQVSIf.9JEb0BEVEEA'
>>> # it can be parsed into options
>>> hobj = pbkdf2_sha512.from_string(h)
>>> rounds, salt, chk = hobj.rounds, hobj.salt, hobj.checksum
>>> # and a new grub hash can be created
>>> gobj = grub_pbkdf2_sha512(rounds=rounds, salt=salt, checksum=chk)
>>> g = gobj.to_string()
>>> g
>>> grub_pbkdf2_sha512.verify("password", g)
True
.. rubric:: Footnotes
.. [#grub] Information about Grub's password hashes - `<http://grub.enbug.org/Authentication>`_.
.. [#pbkdf2] The specification for the PBKDF2 algorithm - `<http://tools.ietf.org/html/rfc2898#section-5.2>`_.
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