mirror of
https://github.com/python/cpython.git
synced 2024-12-05 07:43:50 +08:00
99 lines
3.4 KiB
ReStructuredText
99 lines
3.4 KiB
ReStructuredText
:mod:`hmac` --- Keyed-Hashing for Message Authentication
|
|
========================================================
|
|
|
|
.. module:: hmac
|
|
:synopsis: Keyed-Hashing for Message Authentication (HMAC) implementation
|
|
for Python.
|
|
.. moduleauthor:: Gerhard Häring <ghaering@users.sourceforge.net>
|
|
.. sectionauthor:: Gerhard Häring <ghaering@users.sourceforge.net>
|
|
|
|
**Source code:** :source:`Lib/hmac.py`
|
|
|
|
--------------
|
|
|
|
This module implements the HMAC algorithm as described by :rfc:`2104`.
|
|
|
|
|
|
.. function:: new(key, msg=None, digestmod=None)
|
|
|
|
Return a new hmac object. *key* is a bytes or bytearray object giving the
|
|
secret key. If *msg* is present, the method call ``update(msg)`` is made.
|
|
*digestmod* is the digest constructor or module for the HMAC object to use.
|
|
It defaults to the :data:`hashlib.md5` constructor.
|
|
|
|
.. versionchanged:: 3.4
|
|
Parameter *key* can be a bytes or bytearray object. Parameter *msg* can
|
|
be of any type supported by :mod:`hashlib`.
|
|
|
|
An HMAC object has the following methods:
|
|
|
|
.. method:: HMAC.update(msg)
|
|
|
|
Update the hmac object with *msg*. Repeated calls are equivalent to a
|
|
single call with the concatenation of all the arguments:
|
|
``m.update(a); m.update(b)`` is equivalent to ``m.update(a + b)``.
|
|
|
|
.. versionchanged:: 3.4
|
|
Parameter *msg* can be of any type supported by :mod:`hashlib`.
|
|
|
|
|
|
.. method:: HMAC.digest()
|
|
|
|
Return the digest of the bytes passed to the :meth:`update` method so far.
|
|
This bytes object will be the same length as the *digest_size* of the digest
|
|
given to the constructor. It may contain non-ASCII bytes, including NUL
|
|
bytes.
|
|
|
|
.. warning::
|
|
|
|
When comparing the output of :meth:`digest` to an externally-supplied
|
|
digest during a verification routine, it is recommended to use the
|
|
:func:`compare_digest` function instead of the ``==`` operator
|
|
to reduce the vulnerability to timing attacks.
|
|
|
|
|
|
.. method:: HMAC.hexdigest()
|
|
|
|
Like :meth:`digest` except the digest is returned as a string twice the
|
|
length containing only hexadecimal digits. This may be used to exchange the
|
|
value safely in email or other non-binary environments.
|
|
|
|
.. warning::
|
|
|
|
When comparing the output of :meth:`hexdigest` to an externally-supplied
|
|
digest during a verification routine, it is recommended to use the
|
|
:func:`compare_digest` function instead of the ``==`` operator
|
|
to reduce the vulnerability to timing attacks.
|
|
|
|
|
|
.. method:: HMAC.copy()
|
|
|
|
Return a copy ("clone") of the hmac object. This can be used to efficiently
|
|
compute the digests of strings that share a common initial substring.
|
|
|
|
|
|
This module also provides the following helper function:
|
|
|
|
.. function:: compare_digest(a, b)
|
|
|
|
Return ``a == b``. This function uses an approach designed to prevent
|
|
timing analysis by avoiding content-based short circuiting behaviour,
|
|
making it appropriate for cryptography. *a* and *b* must both be of the
|
|
same type: either :class:`str` (ASCII only, as e.g. returned by
|
|
:meth:`HMAC.hexdigest`), or a :term:`bytes-like object`.
|
|
|
|
.. note::
|
|
|
|
If *a* and *b* are of different lengths, or if an error occurs,
|
|
a timing attack could theoretically reveal information about the
|
|
types and lengths of *a* and *b*--but not their values.
|
|
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
|
|
.. seealso::
|
|
|
|
Module :mod:`hashlib`
|
|
The Python module providing secure hash functions.
|