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.. hazmat::
Backend Interfaces
==================
.. currentmodule:: cryptography.hazmat.backends.interfaces
Backend implementations may provide a number of interfaces to support operations
such as :doc:`/hazmat/primitives/symmetric-encryption`,
:doc:`/hazmat/primitives/cryptographic-hashes`, and
:doc:`/hazmat/primitives/hmac`.
A specific ``backend`` may provide one or more of these interfaces.
.. class:: CipherBackend
A backend which provides methods for using ciphers for encryption
and decryption.
.. method:: cipher_supported(cipher, mode)
Check if a ``cipher`` and ``mode`` combination is supported by
this backend.
:param cipher: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
provider.
:param mode: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
:returns: ``True`` if the specified ``cipher`` and ``mode`` combination
is supported by this backend, otherwise ``False``
.. method:: create_symmetric_encryption_ctx(cipher, mode)
Create a
:class:`~cryptogrpahy.hazmat.primitives.interfaces.CipherContext` that
can be used for encrypting data with the symmetric ``cipher`` using
the given ``mode``.
:param cipher: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
provider.
:param mode: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
:returns:
:class:`~cryptography.hazmat.primitives.interfaces.CipherContext`
:raises ValueError: When tag is not None in an AEAD mode
.. method:: create_symmetric_decryption_ctx(cipher, mode)
Create a
:class:`~cryptogrpahy.hazmat.primitives.interfaces.CipherContext` that
can be used for decrypting data with the symmetric ``cipher`` using
the given ``mode``.
:param cipher: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm`
provider.
:param mode: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.Mode` provider.
:returns:
:class:`~cryptography.hazmat.primitives.interfaces.CipherContext`
:raises ValueError: When tag is None in an AEAD mode
.. class:: HashBackend
A backend with methods for using cryptographic hash functions.
.. method:: hash_supported(algorithm)
Check if the specified ``algorithm`` is supported by this backend.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:returns: ``True`` if the specified ``algorithm`` is supported by this
backend, otherwise ``False``.
.. method:: create_hash_ctx(algorithm)
Create a
:class:`~cryptogrpahy.hazmat.primitives.interfaces.HashContext` that
uses the specified ``algorithm`` to calculate a message digest.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:returns:
:class:`~cryptography.hazmat.primitives.interfaces.HashContext`
.. class:: HMACBackend
A backend with methods for using cryptographic hash functions as message
authentication codes.
.. method:: hmac_supported(algorithm)
Check if the specified ``algorithm`` is supported by this backend.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:returns: ``True`` if the specified ``algorithm`` is supported for HMAC
by this backend, otherwise ``False``.
.. method:: create_hmac_ctx(algorithm)
Create a
:class:`~cryptogrpahy.hazmat.primitives.interfaces.HashContext` that
uses the specified ``algorithm`` to calculate a hash-based message
authentication code.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:returns:
:class:`~cryptography.hazmat.primitives.interfaces.HashContext`
.. class:: PBKDF2Backend
A backend with methods for using PBKDF2.
.. method:: pbkdf2_hash_supported(algorithm)
Check if the specified ``algorithm`` is supported by this backend.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider.
:returns: ``True`` if the specified ``algorithm`` is supported for
PBKDF2 by this backend, otherwise ``False``.
.. method:: derive_pbkdf2(self, algorithm, length, salt, iterations,
key_material)
: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.
:param int iterations: The number of iterations to perform of the hash
function.
:param bytes key_material: The key material to use as a basis for
the derived key. This is typically a password.
:return bytes: Derived key.
|
