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.. hazmat::
Key Derivation Functions
========================
.. currentmodule:: cryptography.hazmat.primitives.kdf
Key derivation functions derive key material from information such as passwords
using a pseudo-random function (PRF).
.. class:: PBKDF2(algorithm, length, salt, iterations, backend):
.. doctest::
>>> from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2
>>> from cryptography.hazmat.backends import default_backend
>>> backend = default_backend()
>>> salt = os.urandom(16)
>>> # derive
>>> kdf = PBKDF2(hashes.SHA1(), 20, salt, 10000, backend)
>>> key = kdf.derive(b"my great password")
>>> # verify
>>> kdf = PBKDF2(hashes.SHA1(), 20, salt, 10000, backend)
>>> kdf.verify(b"my great password", key)
None
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:param int length: The desired length of the derived key. Maximum is
2\ :sup:`31` - 1.
:param bytes salt: A salt. `NIST SP 800-132`_ recommends 128-bits or
longer.
:param int iterations: The number of iterations to perform of the hash
function.
.. _`NIST SP 800-132`: http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf
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