diff options
Diffstat (limited to 'docs/hazmat')
| -rw-r--r-- | docs/hazmat/backends/interfaces.rst | 2 | ||||
| -rw-r--r-- | docs/hazmat/primitives/index.rst | 3 | ||||
| -rw-r--r-- | docs/hazmat/primitives/mac/cmac.rst | 100 | ||||
| -rw-r--r-- | docs/hazmat/primitives/mac/hmac.rst (renamed from docs/hazmat/primitives/hmac.rst) | 0 | ||||
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 4 |
5 files changed, 105 insertions, 4 deletions
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst index 71cd4564..3ed4cfb6 100644 --- a/docs/hazmat/backends/interfaces.rst +++ b/docs/hazmat/backends/interfaces.rst @@ -9,7 +9,7 @@ Backend 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`. +:doc:`/hazmat/primitives/mac/hmac`. A specific ``backend`` may provide one or more of these interfaces. diff --git a/docs/hazmat/primitives/index.rst b/docs/hazmat/primitives/index.rst index 90deec8b..2b92c43e 100644 --- a/docs/hazmat/primitives/index.rst +++ b/docs/hazmat/primitives/index.rst @@ -7,7 +7,8 @@ Primitives :maxdepth: 1 cryptographic-hashes - hmac + mac/hmac + mac/cmac symmetric-encryption padding key-derivation-functions diff --git a/docs/hazmat/primitives/mac/cmac.rst b/docs/hazmat/primitives/mac/cmac.rst new file mode 100644 index 00000000..90d94ed8 --- /dev/null +++ b/docs/hazmat/primitives/mac/cmac.rst @@ -0,0 +1,100 @@ +.. hazmat:: + +Cipher-based message authentication code +======================================== + +.. currentmodule:: cryptography.hazmat.primitives.cmac + +.. testsetup:: + + import binascii + key = binascii.unhexlify(b"0" * 32) + +Cipher-based message authentication codes (or CMACs) are a tool for calculating +message authentication codes using a block cipher coupled with a +secret key. You can use an CMAC to verify both the integrity and authenticity +of a message. + +.. class:: CMAC(algorithm, backend) + + CMAC objects take a + :class:`~cryptography.hazmat.primitives.interfaces.BlockCipherAlgorithm` provider. + + .. doctest:: + + >>> from cryptography.hazmat.backends import default_backend + >>> from cryptography.hazmat.primitives import cmac + >>> from cryptography.hazmat.primitives.ciphers import algorithms + >>> c = cmac.CMAC(algorithms.AES(key), backend=default_backend()) + >>> c.update(b"message to authenticate") + >>> c.finalize() + 'CT\x1d\xc8\x0e\x15\xbe4e\xdb\xb6\x84\xca\xd9Xk' + + If the backend doesn't support the requested ``algorithm`` an + :class:`~cryptography.exceptions.UnsupportedAlgorithm` exception will be + raised. + + If the `algorithm`` isn't a + :class:`~cryptography.primitives.interfaces.BlockCipherAlgorithm` provider, + ``TypeError`` will be raised. + + To check that a given signature is correct use the :meth:`verify` method. + You will receive an exception if the signature is wrong: + + .. code-block:: pycon + + >>> c.verify(b"an incorrect signature") + Traceback (most recent call last): + ... + cryptography.exceptions.InvalidSignature: Signature did not match digest. + + :param algorithm: An + :class:`~cryptography.hazmat.primitives.interfaces.BlockCipherAlgorithm` + provider. + :param backend: An + :class:`~cryptography.hazmat.backends.interfaces.CMACBackend` + provider. + :raises TypeError: This is raised if the provided ``algorithm`` is not an instance of + :class:`~cryptography.hazmat.primitives.interfaces.BlockCipherAlgorithm` + :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised if the + provided ``backend`` does not implement + :class:`~cryptography.hazmat.backends.interfaces.CMACBackend` + + .. method:: update(data) + + :param bytes data: The bytes to hash and authenticate. + :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize` + + .. method:: copy() + + Copy this :class:`CMAC` instance, usually so that we may call + :meth:`finalize` to get an intermediate value while we continue + to call :meth:`update` on the original instance. + + :return: A new instance of :class:`CMAC` that can be updated + and finalized independently of the original instance. + :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize` + + .. method:: verify(signature) + + Finalize the current context and securely compare the MAC to + ``signature``. + + :param bytes signature: The bytes to compare the current CMAC + against. + :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize` + :raises cryptography.exceptions.InvalidSignature: If signature does not + match digest + + .. method:: finalize() + + Finalize the current context and return the message authentication code + as bytes. + + After ``finalize`` has been called this object can no longer be used + and :meth:`update`, :meth:`copy`, :meth:`verify` and :meth:`finalize` + will raise an :class:`~cryptography.exceptions.AlreadyFinalized` + exception. + + :return bytes: The message authentication code as bytes. + :raises cryptography.exceptions.AlreadyFinalized: diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/mac/hmac.rst index 11b10735..11b10735 100644 --- a/docs/hazmat/primitives/hmac.rst +++ b/docs/hazmat/primitives/mac/hmac.rst diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index 1a4df222..c2692ae2 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -21,7 +21,7 @@ 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 </hazmat/primitives/hmac>`, in +message authentication code, such as :doc:`HMAC </hazmat/primitives/mac/hmac>`, in an "encrypt-then-MAC" formulation as `described by Colin Percival`_. .. class:: Cipher(algorithm, mode, backend) @@ -289,7 +289,7 @@ Modes block cipher mode that simultaneously encrypts the message as well as authenticating it. Additional unencrypted data may also be authenticated. Additional means of verifying integrity such as - :doc:`HMAC </hazmat/primitives/hmac>` are not necessary. + :doc:`HMAC </hazmat/primitives/mac/hmac>` are not necessary. **This mode does not require padding.** |