/Doc/library/hmac.rst

 1
 2:mod:`hmac` --- Keyed-Hashing for Message Authentication
 3========================================================
 4
 5.. module:: hmac
 6   :synopsis: Keyed-Hashing for Message Authentication (HMAC) implementation for Python.
 7.. moduleauthor:: Gerhard H채ring <ghaering@users.sourceforge.net>
 8.. sectionauthor:: Gerhard H채ring <ghaering@users.sourceforge.net>
 9
10
11.. versionadded:: 2.2
12
13This module implements the HMAC algorithm as described by :rfc:`2104`.
14
15
16.. function:: new(key[, msg[, digestmod]])
17
18   Return a new hmac object.  If *msg* is present, the method call ``update(msg)``
19   is made. *digestmod* is the digest constructor or module for the HMAC object to
20   use. It defaults to  the :func:`hashlib.md5` constructor.
21
22   .. note::
23
24      The md5 hash has known weaknesses but remains the default for backwards
25      compatibility. Choose a better one for your application.
26
27An HMAC object has the following methods:
28
29
30.. method:: hmac.update(msg)
31
32   Update the hmac object with the string *msg*.  Repeated calls are equivalent to
33   a single call with the concatenation of all the arguments: ``m.update(a);
34   m.update(b)`` is equivalent to ``m.update(a + b)``.
35
36
37.. method:: hmac.digest()
38
39   Return the digest of the strings passed to the :meth:`update` method so far.
40   This string will be the same length as the *digest_size* of the digest given to
41   the constructor.  It may contain non-ASCII characters, including NUL bytes.
42
43
44.. method:: hmac.hexdigest()
45
46   Like :meth:`digest` except the digest is returned as a string twice the length
47   containing only hexadecimal digits.  This may be used to exchange the value
48   safely in email or other non-binary environments.
49
50
51.. method:: hmac.copy()
52
53   Return a copy ("clone") of the hmac object.  This can be used to efficiently
54   compute the digests of strings that share a common initial substring.
55
56
57.. seealso::
58
59   Module :mod:`hashlib`
60      The python module providing secure hash functions.
61