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.. 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())
... )
|
