Issue #10924: Adding salt and Modular Crypt Format to crypt library.

This commit is contained in:
Sean Reifscheider 2011-02-22 10:55:44 +00:00
parent f3042782af
commit e2dfefbe85
7 changed files with 183 additions and 13 deletions

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@ -15,9 +15,9 @@
This module implements an interface to the :manpage:`crypt(3)` routine, which is
a one-way hash function based upon a modified DES algorithm; see the Unix man
page for further details. Possible uses include allowing Python scripts to
accept typed passwords from the user, or attempting to crack Unix passwords with
a dictionary.
page for further details. Possible uses include storing hashed passwords
so you can check passwords without storing the actual password, or attempting
to crack Unix passwords with a dictionary.
.. index:: single: crypt(3)
@ -26,15 +26,67 @@ the :manpage:`crypt(3)` routine in the running system. Therefore, any
extensions available on the current implementation will also be available on
this module.
Hashing Methods
---------------
.. function:: crypt(word, salt)
The :mod:`crypt` module defines the list of hashing methods (not all methods
are available on all platforms):
.. data:: METHOD_SHA512
A Modular Crypt Format method with 16 character salt and 86 character
hash. This is the strongest method.
.. versionadded:: 3.3
.. data:: METHOD_SHA256
Another Modular Crypt Format method with 16 character salt and 43
character hash.
.. versionadded:: 3.3
.. data:: METHOD_MD5
Another Modular Crypt Format method with 8 character salt and 22
character hash.
.. versionadded:: 3.3
.. data:: METHOD_CRYPT
The traditional method with a 2 character salt and 13 characters of
hash. This is the weakest method.
.. versionadded:: 3.3
Module Functions
----------------
The :mod:`crypt` module defines the following functions:
.. function:: crypt(word, salt=None)
*word* will usually be a user's password as typed at a prompt or in a graphical
interface. *salt* is usually a random two-character string which will be used
to perturb the DES algorithm in one of 4096 ways. The characters in *salt* must
be in the set ``[./a-zA-Z0-9]``. Returns the hashed password as a string, which
will be composed of characters from the same alphabet as the salt (the first two
characters represent the salt itself).
interface. The optional *salt* is either a string as returned from
:func:`mksalt`, one of the ``crypt.METHOD_*`` values (though not all
may be available on all platforms), or a full encrypted password
including salt, as returned by this function. If *salt* is not
provided, the strongest method will be used (as returned by
:func:`methods`.
Checking a password is usually done by passing the plain-text password
as *word* and the full results of a previous :func:`crypt` call,
which should be the same as the results of this call.
*salt* (either a random 2 or 16 character string, possibly prefixed with
``$digit$`` to indicate the method) which will be used to perturb the
encryption algorithm. The characters in *salt* must be in the set
``[./a-zA-Z0-9]``, with the exception of Modular Crypt Format which
prefixes a ``$digit$``.
Returns the hashed password as a string, which will be composed of
characters from the same alphabet as the salt.
.. index:: single: crypt(3)
@ -42,6 +94,34 @@ this module.
different sizes in the *salt*, it is recommended to use the full crypted
password as salt when checking for a password.
.. versionchanged:: 3.3
Before version 3.3, *salt* must be specified as a string and cannot
accept ``crypt.METHOD_*`` values (which don't exist anyway).
.. function:: methods()
Return a list of available password hashing algorithms, as
``crypt.METHOD_*`` objects. This list is sorted from strongest to
weakest, and is guaranteed to have at least ``crypt.METHOD_CRYPT``.
.. versionadded:: 3.3
.. function:: mksalt(method=None)
Return a randomly generated salt of the specified method. If no
*method* is given, the strongest method available as returned by
:func:`methods` is used.
The return value is a string either of 2 characters in length for
``crypt.METHOD_CRYPT``, or 19 characters starting with ``$digit$`` and
16 random characters from the set ``[./a-zA-Z0-9]``, suitable for
passing as the *salt* argument to :func:`crypt`.
.. versionadded:: 3.3
Examples
--------
A simple example illustrating typical use::
import crypt, getpass, pwd
@ -57,3 +137,11 @@ A simple example illustrating typical use::
else:
return 1
To generate a hash of a password using the strongest available method and
check it against the original::
import crypt
hashed = crypt.crypt(plaintext)
if hashed != crypt.crypt(plaintext, hashed):
raise "Hashed version doesn't validate against original"

61
Lib/crypt.py Normal file
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@ -0,0 +1,61 @@
'''Wrapper to the POSIX crypt library call and associated functionality.
'''
import _crypt
saltchars = 'abcdefghijklmnopqrstuvwxyz'
saltchars += saltchars.upper()
saltchars += '0123456789./'
class _MethodClass:
'''Class representing a salt method per the Modular Crypt Format or the
legacy 2-character crypt method.'''
def __init__(self, name, ident, salt_chars, total_size):
self.name = name
self.ident = ident
self.salt_chars = salt_chars
self.total_size = total_size
def __repr__(self):
return '<crypt.METHOD_%s>' % self.name
# available salting/crypto methods
METHOD_CRYPT = _MethodClass('CRYPT', None, 2, 13)
METHOD_MD5 = _MethodClass('MD5', '1', 8, 34)
METHOD_SHA256 = _MethodClass('SHA256', '5', 16, 63)
METHOD_SHA512 = _MethodClass('SHA512', '6', 16, 106)
def methods():
'''Return a list of methods that are available in the platform ``crypt()``
library, sorted from strongest to weakest. This is guaranteed to always
return at least ``[METHOD_CRYPT]``'''
method_list = [ METHOD_SHA512, METHOD_SHA256, METHOD_MD5 ]
ret = [ method for method in method_list
if len(crypt('', method)) == method.total_size ]
ret.append(METHOD_CRYPT)
return ret
def mksalt(method = None):
'''Generate a salt for the specified method. If not specified, the
strongest available method will be used.'''
import random
if method == None: method = methods()[0]
s = '$%s$' % method.ident if method.ident else ''
s += ''.join([ random.choice(saltchars) for x in range(method.salt_chars) ])
return(s)
def crypt(word, salt = None):
'''Return a string representing the one-way hash of a password, preturbed
by a salt. If ``salt`` is not specified or is ``None``, the strongest
available method will be selected and a salt generated. Otherwise,
``salt`` may be one of the ``crypt.METHOD_*`` values, or a string as
returned by ``crypt.mksalt()``.'''
if salt == None: salt = mksalt()
elif isinstance(salt, _MethodClass): salt = mksalt(salt)
return(_crypt.crypt(word, salt))

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@ -10,6 +10,23 @@ class CryptTestCase(unittest.TestCase):
if support.verbose:
print('Test encryption: ', c)
def test_salt(self):
self.assertEqual(len(crypt.saltchars), 64)
for method in crypt.methods():
salt = crypt.mksalt(method)
self.assertEqual(len(salt),
method.salt_chars + (3 if method.ident else 0))
def test_saltedcrypt(self):
for method in crypt.methods():
pw = crypt.crypt('assword', method)
self.assertEqual(len(pw), method.total_size)
pw = crypt.crypt('assword', crypt.mksalt(method))
self.assertEqual(len(pw), method.total_size)
def test_methods(self):
self.assertTrue(len(crypt.methods()) > 1)
def test_main():
support.run_unittest(CryptTestCase)

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@ -27,6 +27,10 @@ Core and Builtins
Library
-------
- Issue #10924: Adding salt and Modular Crypt Format to crypt library.
Moved old C wrapper to _crypt, and added a Python wrapper with
enhanced salt generation and simpler API for password generation.
- Issue #11074: Make 'tokenize' so it can be reloaded.
- Issue #11085: Moved collections abstract base classes into a separate

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@ -207,7 +207,7 @@ _symtable symtablemodule.c
#
# First, look at Setup.config; configure may have set this for you.
#crypt cryptmodule.c # -lcrypt # crypt(3); needs -lcrypt on some systems
#_crypt _cryptmodule.c # -lcrypt # crypt(3); needs -lcrypt on some systems
# Some more UNIX dependent modules -- off by default, since these

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@ -45,7 +45,7 @@ static PyMethodDef crypt_methods[] = {
static struct PyModuleDef cryptmodule = {
PyModuleDef_HEAD_INIT,
"crypt",
"_crypt",
NULL,
-1,
crypt_methods,
@ -56,7 +56,7 @@ static struct PyModuleDef cryptmodule = {
};
PyMODINIT_FUNC
PyInit_crypt(void)
PyInit__crypt(void)
{
return PyModule_Create(&cryptmodule);
}

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@ -636,7 +636,7 @@ class PyBuildExt(build_ext):
libs = ['crypt']
else:
libs = []
exts.append( Extension('crypt', ['cryptmodule.c'], libraries=libs) )
exts.append( Extension('_crypt', ['_cryptmodule.c'], libraries=libs) )
# CSV files
exts.append( Extension('_csv', ['_csv.c']) )