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=================================================================
:class:`passlib.hash.cta_pbkdf2_sha1` - Cryptacular's PBKDF2 hash
=================================================================
.. index:: pbkdf2 hash; Cryptacular
.. currentmodule:: passlib.hash
This class provides an implementation of Cryptacular's
PBKDF2-HMAC-SHA1 hash format [#cta]_. 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:`dlitz_pbkdf2_sha1 <passlib.hash.dlitz_pbkdf2_sha1>`
for another hash which looks almost exactly like this one.
Interface
=========
.. autoclass:: cta_pbkdf2_sha1()
Format & Algorithm
==================
A example hash (of ``password``) is:
``$p5k2$2710$oX9ZZOcNgYoAsYL-8bqxKg==$AU2JLf2rNxWoZxWxRCluY0u6h6c=``
All of this scheme's hashes have the format :samp:`$p5k2${rounds}${salt}${checksum}`,
where:
* ``$p5k2$`` is used as the :ref:`modular-crypt-format` identifier.
* :samp:`{rounds}` is the number of PBKDF2 iterations to perform,
stored as lowercase hexadecimal number with no zero-padding (in the example: ``2710`` or 10000 iterations).
* :samp:`{salt}` is the salt string encoding using
base64 (with ``-_`` as the high values).
``oX9ZZOcNgYoAsYL-8bqxKg==`` in the example.
* :samp:`{checksum}` is 28 characters encoding
the resulting 20-byte PBKDF2 derived key using
base64 (with ``-_`` as the high values).
``AU2JLf2rNxWoZxWxRCluY0u6h6c=`` in the example.
In order to generate the checksum, the password is first encoded into UTF-8 if it's unicode.
The salt is decoded from its base64 representation.
PBKDF2 is called using the encoded password, the full salt,
the specified number of rounds, and using HMAC-SHA1 as its pseudorandom function.
20 bytes of derived key are requested, and the resulting key is encoded and used
as the checksum portion of the hash.
.. rubric:: Footnotes
.. [#cta] The reference for this hash format - `<https://bitbucket.org/dholth/cryptacular/>`_.
.. [#pbkdf2] The specification for the PBKDF2 algorithm - `<http://tools.ietf.org/html/rfc2898#section-5.2>`_.
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