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.. hazmat::
Padding
=======
.. currentmodule:: cryptography.hazmat.primitives.asymmetric.padding
.. warning::
`Padding is critical`_ when signing or encrypting data using RSA. Without
correct padding signatures can be forged, messages decrypted, and private
keys compromised.
.. class:: PSS(mgf, salt_length)
.. versionadded:: 0.3
.. versionchanged:: 0.4
Added ``salt_length`` parameter.
PSS (Probabilistic Signature Scheme) is a signature scheme defined in
:rfc:`3447`. It is more complex than PKCS1 but possesses a `security proof`_.
This is the `recommended padding algorithm`_ for RSA signatures. It cannot
be used with RSA encryption.
:param mgf: A mask generation function object. At this time the only
supported MGF is :class:`MGF1`.
:param int salt_length: The length of the salt. It is recommended that this
be set to ``PSS.MAX_LENGTH``.
.. attribute:: MAX_LENGTH
Pass this attribute to ``salt_length`` to get the maximum salt length
available.
.. class:: OAEP(mgf, label)
.. versionadded:: 0.4
OAEP (Optimal Asymmetric Encryption Padding) is a padding scheme defined in
:rfc:`3447`. It provides probabilistic encryption and is `proven secure`_
against several attack types. This is the `recommended padding algorithm`_
for RSA encryption. It cannot be used with RSA signing.
:param mgf: A mask generation function object. At this time the only
supported MGF is :class:`MGF1`.
:param bytes label: A label to apply. This is a rarely used field and
should typically be set to ``None`` or ``b""``, which are equivalent.
.. class:: PKCS1v15()
.. versionadded:: 0.3
PKCS1 v1.5 (also known as simply PKCS1) is a simple padding scheme
developed for use with RSA keys. It is defined in :rfc:`3447`. This padding
can be used for signing and encryption.
Mask generation functions
~~~~~~~~~~~~~~~~~~~~~~~~~
.. class:: MGF1(algorithm)
.. versionadded:: 0.3
.. versionchanged:: 0.6
Removed the deprecated ``salt_length`` parameter.
MGF1 (Mask Generation Function 1) is used as the mask generation function
in :class:`PSS` padding. It takes a hash algorithm and a salt length.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
.. _`Padding is critical`: http://rdist.root.org/2009/10/06/why-rsa-encryption-padding-is-critical/
.. _`security proof`: http://eprint.iacr.org/2001/062.pdf
.. _`recommended padding algorithm`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html
.. _`proven secure`: http://cseweb.ucsd.edu/users/mihir/papers/oae.pdf
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