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: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.
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