blob: b8f94fd22e1c77fb3209093f4d8b118a19b886f9 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
.. hazmat::
Hash-based Message Authentication Codes
=======================================
.. currentmodule:: cryptography.hazmat.primitives.hmac
.. testsetup::
import binascii
key = binascii.unhexlify(b"0" * 32)
Hash-based message authentication codes (or HMACs) are a tool for calculating
message authentication codes using a cryptographic hash function coupled with a
secret key. You can use an HMAC to verify integrity as well as authenticate a
message.
.. class:: HMAC(key, algorithm, backend)
HMAC objects take a ``key`` and a provider of
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`.
The ``key`` should be randomly generated bytes and is recommended to be
equal in length to the ``digest_size`` of the hash function chosen.
You must keep the ``key`` secret.
This is an implementation of :rfc:`2104`.
.. doctest::
>>> from cryptography.hazmat.backends import default_backend
>>> from cryptography.hazmat.primitives import hashes, hmac
>>> h = hmac.HMAC(key, hashes.SHA256(), backend=default_backend())
>>> h.update(b"message to hash")
>>> h.finalize()
'#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J'
If the backend doesn't support the requested ``algorithm`` an
:class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised.
:param key: Secret key as ``bytes``.
:param algorithm: A
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
provider such as those described in
:ref:`Cryptographic Hashes <cryptographic-hash-algorithms>`.
:param backend: A
:class:`~cryptography.hazmat.backends.interfaces.HMACBackend`
provider.
.. method:: update(msg)
:param bytes msg: The bytes to hash and authenticate.
:raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
.. method:: copy()
Copy this :class:`HMAC` instance, usually so that we may call
:meth:`finalize` and get an intermediate digest value while we continue
to call :meth:`update` on the original.
:return: A new instance of :class:`HMAC` which can be updated
and finalized independently of the original instance.
:raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
.. method:: finalize()
Finalize the current context and return the message digest as bytes.
Once ``finalize`` is called this object can no longer be used and
:meth:`update`, :meth:`copy`, and :meth:`finalize` will raise
:class:`~cryptography.exceptions.AlreadyFinalized`.
:return bytes: The message digest as bytes.
:raises cryptography.exceptions.AlreadyFinalized:
.. method:: verify(signature)
Finalize the current context and securely compare digest to ``signature``.
:param bytes signature: The bytes of the HMAC signature recieved.
:raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
:raises cryptography.exceptions.InvalidSignature: If signature does not match digest
|
