
``hmac`` --- Keyed-Hashing for Message Authentication
*****************************************************

This module implements the HMAC algorithm as described by **RFC
2104**.

hmac.new(key, msg=None, digestmod=None)

   Return a new hmac object.  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
   ``hashlib.md5()`` constructor.

   Note: The md5 hash has known weaknesses but remains the default for
     backwards compatibility. Choose a better one for your
     application.

An HMAC object has the following methods:

hmac.update(msg)

   Update the hmac object with the string *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)``.

hmac.digest()

   Return the digest of the strings passed to the ``update()`` method
   so far. This string will be the same length as the *digest_size* of
   the digest given to the constructor.  It may contain non-ASCII
   characters, including NUL bytes.

hmac.hexdigest()

   Like ``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.

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.

See also:

   Module ``hashlib``
      The python module providing secure hash functions.
