cpython/Doc/library/hashlib.rst
Benjamin Peterson 058e31ef2a Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

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  r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines

  Fix issue 4884, preventing a crash in the socket code when python is compiled
  with llvm-gcc and run with a glibc <2.10.
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  r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line

  Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library.
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  r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line

  Corrected an incorrect self-reference.
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  r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line

  rewrite verbose conditionals
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  r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line

  tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901
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  r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line

  Corrected minor typo and added .currentmodule directives to fix missing cross-references.
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  r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line

  make tests fail if they can't be imported
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  r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line

  move seealso to a more appropiate place
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  r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line

  macos 9 isn't supported
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  r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines

  correct email address
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  r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines

  Update the documentation for binascii and zlib crc32/adler32 functions
  to better describe the signed vs unsigned return value behavior on
  different platforms and versions of python.  Mention the workaround to
  make them all return the same thing by using & 0xffffffff.

  Fixes issue4903.

  Also needs to be merged into release26-maint, release30-maint, & py3k.
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  r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line

  add email addresses
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  r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line

  Minor changes/corrections in markup.
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  r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line

  small logic correction
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  r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines

  Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard().

  Needs to be backported to 2.6 and forward ported to 3.0 and 3.1.
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  r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines

  ast.literal_eval can properly evaluate complex numbers now.  This fixes issue4907.
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  r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line

  Note that first coord. is left alone
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  r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line

  Fix refcount leak in error cases.  Bug found by coverity.
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  r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines

  Use assertRaises.
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  r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines

  #1162154: inspect.getmembers() now skips attributes that raise AttributeError,
  e.g. a __slots__ attribute which has not been set.
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  r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line

  Made minor changes/corrections in markup. Added a couple of section headings.
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  r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line

  Minor changes/corrections in markup.
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  r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line

  compare with == not is #4946
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2009-01-16 03:54:08 +00:00

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ReStructuredText

:mod:`hashlib` --- Secure hashes and message digests
====================================================
.. module:: hashlib
:synopsis: Secure hash and message digest algorithms.
.. moduleauthor:: Gregory P. Smith <greg@krypto.org>
.. sectionauthor:: Gregory P. Smith <greg@krypto.org>
.. index::
single: message digest, MD5
single: secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512
This module implements a common interface to many different secure hash and
message digest algorithms. Included are the FIPS secure hash algorithms SHA1,
SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA's MD5
algorithm (defined in Internet :rfc:`1321`). The terms "secure hash" and
"message digest" are interchangeable. Older algorithms were called message
digests. The modern term is secure hash.
.. note::
If you want the adler32 or crc32 hash functions they are available in
the :mod:`zlib` module.
.. warning::
Some algorithms have known hash collision weaknesses, see the FAQ at the end.
There is one constructor method named for each type of :dfn:`hash`. All return
a hash object with the same simple interface. For example: use :func:`sha1` to
create a SHA1 hash object. You can now feed this object with objects conforming
to the buffer interface (normally :class:`bytes` objects) using the
:meth:`update` method. At any point you can ask it for the :dfn:`digest` of the
concatenation of the data fed to it so far using the :meth:`digest` or
:meth:`hexdigest` methods.
.. note::
For better multithreading performance, the Python GIL is released for
strings of more than 2047 bytes at object creation or on update.
.. note::
Feeding string objects is to :meth:`update` is not supported, as hashes work
on bytes, not on characters.
.. index:: single: OpenSSL; (use in module hashlib)
Constructors for hash algorithms that are always present in this module are
:func:`md5`, :func:`sha1`, :func:`sha224`, :func:`sha256`, :func:`sha384`, and
:func:`sha512`. Additional algorithms may also be available depending upon the
OpenSSL library that Python uses on your platform.
For example, to obtain the digest of the byte string ``b'Nobody inspects the
spammish repetition'``::
>>> import hashlib
>>> m = hashlib.md5()
>>> m.update(b"Nobody inspects")
>>> m.update(b" the spammish repetition")
>>> m.digest()
b'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'
>>> m.digest_size
16
>>> m.block_size
64
More condensed:
>>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest()
'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'
A generic :func:`new` constructor that takes the string name of the desired
algorithm as its first parameter also exists to allow access to the above listed
hashes as well as any other algorithms that your OpenSSL library may offer. The
named constructors are much faster than :func:`new` and should be preferred.
Using :func:`new` with an algorithm provided by OpenSSL:
>>> h = hashlib.new('ripemd160')
>>> h.update(b"Nobody inspects the spammish repetition")
>>> h.hexdigest()
'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc'
The following values are provided as constant attributes of the hash objects
returned by the constructors:
.. data:: digest_size
The size of the resulting hash in bytes.
.. data:: block_size
The internal block size of the hash algorithm in bytes.
A hash object has the following methods:
.. method:: hash.update(arg)
Update the hash object with the object *arg*, which must be interpretable as
a buffer of bytes. 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:: hash.digest()
Return the digest of the data passed to the :meth:`update` method so far.
This is a bytes array of size :attr:`digest_size` which may contain bytes in
the whole range from 0 to 255.
.. method:: hash.hexdigest()
Like :meth:`digest` except the digest is returned as a string object of
double length, containing only hexadecimal digits. This may be used to
exchange the value safely in email or other non-binary environments.
.. method:: hash.copy()
Return a copy ("clone") of the hash object. This can be used to efficiently
compute the digests of data sharing a common initial substring.
.. seealso::
Module :mod:`hmac`
A module to generate message authentication codes using hashes.
Module :mod:`base64`
Another way to encode binary hashes for non-binary environments.
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
The FIPS 180-2 publication on Secure Hash Algorithms.
http://www.cryptography.com/cnews/hash.html
Hash Collision FAQ with information on which algorithms have known issues and
what that means regarding their use.