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crypt.py

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"""Wrapper to the POSIX crypt library call and associated functionality."""

import _crypt

import string as _string

from random import SystemRandom as _SystemRandom

from collections import namedtuple as _namedtuple

_saltchars = _string.ascii_letters + _string.digits + './'

_sr = _SystemRandom()

class _Method(_namedtuple('_Method', 'name ident salt_chars total_size')):

"""Class representing a salt method per the Modular Crypt Format or the

legacy 2-character crypt method."""

def __repr__(self):

return '<crypt.METHOD_{}>'.format(self.name)

def mksalt(method=None):

"""Generate a salt for the specified method.

If not specified, the strongest available method will be used.

"""

if method is None:

method = methods[0]

s = '${}$'.format(method.ident) if method.ident else ''

s += ''.join(_sr.choice(_saltchars) for char in range(method.salt_chars))

return s

def crypt(word, salt=None):

"""Return a string representing the one-way hash of a password, with a salt

prepended.

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 is None or isinstance(salt, _Method):

salt = mksalt(salt)

return _crypt.crypt(word, salt)

# available salting/crypto methods

METHOD_CRYPT = _Method('CRYPT', None, 2, 13)

METHOD_MD5 = _Method('MD5', '1', 8, 34)

METHOD_SHA256 = _Method('SHA256', '5', 16, 63)

METHOD_SHA512 = _Method('SHA512', '6', 16, 106)

methods = []

for _method in (METHOD_SHA512, METHOD_SHA256, METHOD_MD5):

_result = crypt('', _method)

if _result and len(_result) == _method.total_size:

methods.append(_method)

methods.append(METHOD_CRYPT)

del _result, _method