:mod:`sha` --- SHA-1 message digest algorithm

=============================================

.. module:: sha

   :synopsis: NIST's secure hash algorithm, SHA.

   :deprecated:

.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>

.. deprecated:: 2.5

   Use the :mod:`hashlib` module instead.

.. index::

   single: NIST

   single: Secure Hash Algorithm

   single: checksum; SHA

This module implements the interface to NIST's secure hash  algorithm, known as

SHA-1.  SHA-1 is an improved version of the original SHA hash algorithm.  It is

used in the same way as the :mod:`md5` module: use :func:`new` to create an sha

object, then feed this object with arbitrary strings using the :meth:`update`

method, and at any point you can ask it for the :dfn:`digest` of the

concatenation of the strings fed to it so far.  SHA-1 digests are 160 bits

instead of MD5's 128 bits.

.. function:: new([string])

   Return a new sha object.  If *string* is present, the method call

   ``update(string)`` is made.

The following values are provided as constants in the module and as attributes

of the sha objects returned by :func:`new`:

.. data:: blocksize

   Size of the blocks fed into the hash function; this is always ``1``.  This size

   is used to allow an arbitrary string to be hashed.

.. data:: digest_size

   The size of the resulting digest in bytes.  This is always ``20``.

An sha object has the same methods as md5 objects:

.. method:: sha.update(arg)

   Update the sha object with the string *arg*.  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)``.

.. method:: sha.digest()

   Return the digest of the strings passed to the :meth:`update` method so far.

   This is a 20-byte string which may contain non-ASCII characters, including null

   bytes.

.. method:: sha.hexdigest()

   Like :meth:`digest` except the digest is returned as a string of length 40,

   containing only hexadecimal digits.  This may  be used to exchange the value

   safely in email or other non-binary environments.

.. method:: sha.copy()

   Return a copy ("clone") of the sha object.  This can be used to efficiently

   compute the digests of strings that share a common initial substring.

.. seealso::

   `Secure Hash Standard <http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf>`_

      The Secure Hash Algorithm is defined by NIST document FIPS PUB 180-2: `Secure

      Hash Standard

      <http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf>`_,

      published in August 2002.

   `Cryptographic Toolkit (Secure Hashing) <http://csrc.nist.gov/CryptoToolkit/tkhash.html>`_

      Links from NIST to various information on secure hashing.