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Fernet
======
.. currentmodule:: cryptography.fernet
`Fernet`_ is an implementation of symmetric (also known as "secret key")
authenticated cryptography. Fernet provides guarantees that a message encrypted
using it cannot be manipulated or read without the key.
.. class:: Fernet(key)
This class provides both encryption and decryption facilities.
.. doctest::
>>> from cryptography.fernet import Fernet
>>> key = Fernet.generate_key()
>>> f = Fernet(key)
>>> ciphertext = f.encrypt(b"my deep dark secret")
>>> ciphertext
'...'
>>> f.decrypt(ciphertext)
'my deep dark secret'
:param bytes key: A URL-safe base64-encoded 32-byte key. This **must** be
kept secret. Anyone with this key is able to create and
read messages.
.. classmethod:: generate_key()
Generates a fresh fernet key. Keep this some place safe! If you lose it
you'll no longer be able to decrypt messages; if anyone else gains
access to it, they'll be able to decrypt all of your messages.
.. method:: encrypt(plaintext)
:param bytes plaintext: The message you would like to encrypt.
:returns bytes: A secure message which cannot be read or altered
without the key. It is URL-safe base64-encoded.
.. method:: decrypt(ciphertext, ttl=None)
:param bytes ciphertext: An encrypted message.
:param int ttl: Optionally, the number of seconds old a message may be
for it to be valid. If the message is older than
``ttl`` seconds (from the time it was originally
created) an exception will be raised. If ``ttl`` is not
provided (or is ``None``), the age of the message is
not considered.
:returns bytes: The original plaintext.
:raises InvalidToken: If the ``ciphertext`` is in any way invalid, this
exception is raised. A ciphertext may be invalid
for a number of reasons: it is older than the
``ttl``, it is malformed, or it does not have a
valid signature.
.. class:: InvalidToken
See :meth:`Fernet.decrypt` for more information.
.. _`Fernet`: https://github.com/fernet/spec/
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