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[3.10] bpo-42982: update pbkdf2 example & add another link (GH-30966) #30968

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Mar 1, 2022
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[3.10] bpo-42982: update pbkdf2 example & add another link (GH-30966) #30968

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12 changes: 7 additions & 5 deletions Doc/library/hashlib.rst
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Expand Up @@ -251,15 +251,17 @@ include a `salt <https://en.wikipedia.org/wiki/Salt_%28cryptography%29>`_.
The number of *iterations* should be chosen based on the hash algorithm and
computing power. As of 2022, hundreds of thousands of iterations of SHA-256
are suggested. For rationale as to why and how to choose what is best for
your application, read *Appendix A.2.2* of NIST-SP-800-132_.
your application, read *Appendix A.2.2* of NIST-SP-800-132_. The answers
on the `stackexchange pbkdf2 iterations question`_ explain in detail.

*dklen* is the length of the derived key. If *dklen* is ``None`` then the
digest size of the hash algorithm *hash_name* is used, e.g. 64 for SHA-512.

>>> import hashlib
>>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000)
>>> from hashlib import pbkdf2_hmac
>>> our_app_iters = 500_000 # Application specific, read above.
>>> dk = pbkdf2_hmac('sha256', b'password', b'bad salt'*2, our_app_iters)
>>> dk.hex()
'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5'
'15530bba69924174860db778f2c6f8104d3aaf9d26241840c8c4a641c8d000a9'

.. versionadded:: 3.4

Expand Down Expand Up @@ -733,7 +735,7 @@ Domain Dedication 1.0 Universal:
.. _ChaCha: https://cr.yp.to/chacha.html
.. _pyblake2: https://pythonhosted.org/pyblake2/
.. _NIST-SP-800-132: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf

.. _stackexchange pbkdf2 iterations question: https://security.stackexchange.com/questions/3959/recommended-of-iterations-when-using-pbkdf2-sha256/


.. seealso::
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