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	11613 bytes	0644
dsa.rst	13810 bytes	0644
ec.rst	22500 bytes	0644
index.rst	1254 bytes	0644
rsa.rst	23897 bytes	0644
serialization.rst	21721 bytes	0644
utils.rst	2968 bytes	0644
x25519.rst	3352 bytes	0644
File Content: utils.rst

File Content: `utils.rst`
