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lY> Tm qAm\jbѿ 0 : lae Ju@plJbѿ d_a=J Je8q. bѿ ? .. hazmat:: /fernet Symmetric encryption ==================== .. module:: cryptography.hazmat.primitives.ciphers Symmetric encryption is a way to `encrypt`_ or hide the contents of material where the sender and receiver both use the same secret key. Note that symmetric encryption is **not** sufficient for most applications because it only provides secrecy but not authenticity. That means an attacker can't see the message but an attacker can create bogus messages and force the application to decrypt them. For this reason it is **strongly** recommended to combine encryption with a message authentication code, such as :doc:`HMAC `, in an "encrypt-then-MAC" formulation as `described by Colin Percival`_. .. class:: Cipher(algorithm, mode, backend) Cipher objects combine an algorithm such as :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES` with a mode like :class:`~cryptography.hazmat.primitives.ciphers.modes.CBC` or :class:`~cryptography.hazmat.primitives.ciphers.modes.CTR`. A simple example of encrypting and then decrypting content with AES is: .. doctest:: >>> import os >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes >>> from cryptography.hazmat.backends import default_backend >>> backend = default_backend() >>> key = os.urandom(32) >>> iv = os.urandom(16) >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend) >>> encryptor = cipher.encryptor() >>> ct = encryptor.update(b"a secret message") + encryptor.finalize() >>> decryptor = cipher.decryptor() >>> decryptor.update(ct) + decryptor.finalize() 'a secret message' :param algorithms: A :class:`~cryptography.hazmat.primitives.ciphers.CipherAlgorithm` instance such as those described :ref:`below