Edit File: sha.txt
: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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