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.. hazmat::
Interfaces
==========
``cryptography`` uses `Abstract Base Classes`_ as interfaces to describe the
properties and methods of most primitive constructs. Backends may also use
this information to influence their operation. Interfaces should also be used
to document argument and return types.
.. _`Abstract Base Classes`: http://docs.python.org/3.2/library/abc.html
Symmetric Ciphers
~~~~~~~~~~~~~~~~~
.. currentmodule:: cryptography.hazmat.primitives.interfaces
.. class:: CipherAlgorithm
A named symmetric encryption algorithm.
.. attribute:: name
:type: str
The standard name for the mode, for example, "AES", "Camellia", or
"Blowfish".
.. attribute:: key_size
:type: int
The number of bits in the key being used.
.. class:: BlockCipherAlgorithm
A block cipher algorithm.
.. attribute:: block_size
:type: int
The number of bits in a block.
Cipher Modes
------------
Interfaces used by the symmetric cipher modes described in
:ref:`Symmetric Encryption Modes <symmetric-encryption-modes>`.
.. class:: Mode
A named cipher mode.
.. attribute:: name
:type: str
This should be the standard shorthand name for the mode, for example
Cipher-Block Chaining mode is "CBC".
The name may be used by a backend to influence the operation of a
cipher in conjunction with the algorithm's name.
.. method:: validate_for_algorithm(algorithm)
:param CipherAlgorithm algorithm:
Checks that the combination of this mode with the provided algorithm
meets any necessary invariants. This should raise an exception if they
are not met.
For example, the :class:`~cryptography.hazmat.primitives.modes.CBC`
mode uses this method to check that the provided initialization
vector's length matches the block size of the algorithm.
.. class:: ModeWithInitializationVector
A cipher mode with an initialization vector.
.. attribute:: initialization_vector
:type: bytes
Exact requirements of the initialization are described by the
documentation of individual modes.
.. class:: ModeWithNonce
A cipher mode with a nonce.
.. attribute:: nonce
:type: bytes
Exact requirements of the nonce are described by the documentation of
individual modes.
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