Na}{

File Content: utils.rst

.. hazmat::

Asymmetric Utilities
====================

.. currentmodule:: cryptography.hazmat.primitives.asymmetric.utils

.. function:: decode_dss_signature(signature)

Takes in signatures generated by the DSA/ECDSA signers and returns a
    tuple ``(r, s)``. These signatures are ASN.1 encoded ``Dss-Sig-Value``
    sequences (as defined in :rfc:`3279`)

:param bytes signature: The signature to decode.

:returns: The decoded tuple ``(r, s)``.

:raises ValueError: Raised if the signature is malformed.

.. function:: encode_dss_signature(r, s)

Creates an ASN.1 encoded ``Dss-Sig-Value`` (as defined in :rfc:`3279`) from
    raw ``r`` and ``s`` values.

:param int r: The raw signature value ``r``.

:param int s: The raw signature value ``s``.

:return bytes: The encoded signature.

.. class:: Prehashed(algorithm)

.. versionadded:: 1.6

``Prehashed`` can be passed as the ``algorithm`` in the RSA
    :meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey.sign`
    and
    :meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey.verify`
    as well as DSA
    :meth:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKey.sign`
    and
    :meth:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey.verify`
    methods.

For elliptic curves it can be passed as the ``algorithm`` in
    :class:`~cryptography.hazmat.primitives.asymmetric.ec.ECDSA` and then used
    with
    :meth:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey.sign`
    and
    :meth:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey.verify`
    .

:param algorithm: An instance of
        :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`.

.. doctest::

>>> import hashlib
        >>> from cryptography.hazmat.backends import default_backend
        >>> from cryptography.hazmat.primitives import hashes
        >>> from cryptography.hazmat.primitives.asymmetric import (
        ...    padding, rsa, utils
        ... )
        >>> private_key = rsa.generate_private_key(
        ...     public_exponent=65537,
        ...     key_size=2048,
        ...     backend=default_backend()
        ... )
        >>> prehashed_msg = hashlib.sha256(b"A message I want to sign").digest()
        >>> signature = private_key.sign(
        ...     prehashed_msg,
        ...     padding.PSS(
        ...         mgf=padding.MGF1(hashes.SHA256()),
        ...         salt_length=padding.PSS.MAX_LENGTH
        ...     ),
        ...     utils.Prehashed(hashes.SHA256())
        ... )
        >>> public_key = private_key.public_key()
        >>> public_key.verify(
        ...     signature,
        ...     prehashed_msg,
        ...     padding.PSS(
        ...         mgf=padding.MGF1(hashes.SHA256()),
        ...         salt_length=padding.PSS.MAX_LENGTH
        ...     ),
        ...     utils.Prehashed(hashes.SHA256())
        ... )

Name	Size	Permission
dh.rst	8367 bytes	0644
dsa.rst	14134 bytes	0644
ec.rst	19274 bytes	0644
index.rst	1358 bytes	0644
interfaces.rst	648 bytes	0644
rsa.rst	24055 bytes	0644
serialization.rst	17156 bytes	0644
utils.rst	2968 bytes	0644