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Diffstat (limited to 'docs/hazmat/primitives/symmetric-encryption.rst')
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 35 |
1 files changed, 30 insertions, 5 deletions
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index eef359d6..4ab91408 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -12,6 +12,9 @@ Symmetric Encryption key = binascii.unhexlify(b"0" * 32) iv = binascii.unhexlify(b"0" * 32) + from cryptography.hazmat.bindings import default_backend + backend = default_backend() + Symmetric encryption is a way to encrypt (hide the plaintext value) material where the sender and receiver both use the same key. Note that symmetric @@ -22,7 +25,7 @@ For this reason it is *strongly* recommended to combine encryption with a message authentication code, such as :doc:`HMAC </hazmat/primitives/hmac>`, in an "encrypt-then-MAC" formulation as `described by Colin Percival`_. -.. class:: Cipher(algorithm, mode) +.. class:: Cipher(algorithm, mode, backend) Cipher objects combine an algorithm (such as :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES`) with a @@ -34,15 +37,23 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. .. doctest:: >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes - >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv)) + >>> 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: One of the algorithms described below. - :param mode: One of the modes described below. + :param algorithms: A + :class:`~cryptography.hazmat.primitives.interfaces.CipherAlgorithm` + provider such as those described + :ref:`below <symmetric-encryption-algorithms>`. + :param mode: A :class:`~cryptography.hazmat.primitives.interfaces.Mode` + provider such as those described + :ref:`below <symmetric-encryption-modes>`. + :param backend: A + :class:`~cryptography.hazmat.bindings.interfaces.CipherBackend` + provider. .. method:: encryptor() @@ -75,6 +86,15 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. everything into the context. Once that is done call ``finalize()`` to finish the operation and obtain the remainder of the data. + Block ciphers require that plaintext or ciphertext always be a multiple of + their block size, because of that **padding** is often required to make a + message the correct size. ``CipherContext`` will not automatically apply + any padding; you'll need to add your own. For block ciphers the reccomended + padding is :class:`cryptography.hazmat.primitives.padding.PKCS7`. If you + are using a stream cipher mode (such as + :class:`cryptography.hazmat.primitives.modes.CTR`) you don't have to worry + about this. + .. method:: update(data) :param bytes data: The data you wish to pass into the context. @@ -90,11 +110,16 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. .. method:: finalize() :return bytes: Returns the remainder of the data. + :raises ValueError: This is raised when the data provided isn't + correctly padded to be a multiple of the + algorithm's block size. Once ``finalize`` is called this object can no longer be used and :meth:`update` and :meth:`finalize` will raise :class:`~cryptography.exceptions.AlreadyFinalized`. +.. _symmetric-encryption-algorithms: + Algorithms ~~~~~~~~~~ @@ -176,7 +201,7 @@ Weak Ciphers >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes >>> algorithm = algorithms.ARC4(key) - >>> cipher = Cipher(algorithm, mode=None) + >>> cipher = Cipher(algorithm, mode=None, backend=backend) >>> encryptor = cipher.encryptor() >>> ct = encryptor.update(b"a secret message") >>> decryptor = cipher.decryptor() |