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 Häring <ghaering@users.sourceforge.net>

     8 .. sectionauthor:: Gerhard Häring <ghaering@users.sourceforge.net>

     9 

    10 

    11 .. versionadded:: 2.2

    12 

    13 This 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 

    27 An 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