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

import sys as _sys

try:

import _crypt

except ModuleNotFoundError:

if _sys.platform == 'win32':

raise ImportError("The crypt module is not supported on Windows")

else:

raise ImportError("The required _crypt module was not built as part of CPython")

import errno

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, *, rounds=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]

if rounds is not None and not isinstance(rounds, int):

raise TypeError(f'{rounds.__class__.__name__} object cannot be '

f'interpreted as an integer')

if not method.ident: # traditional

s = ''

else: # modular

s = f'${method.ident}$'

if method.ident and method.ident[0] == '2': # Blowfish variants

if rounds is None:

log_rounds = 12

else:

log_rounds = int.bit_length(rounds-1)

if rounds != 1 << log_rounds:

raise ValueError('rounds must be a power of 2')

if not 4 <= log_rounds <= 31:

raise ValueError('rounds out of the range 2**4 to 2**31')

s += f'{log_rounds:02d}$'

elif method.ident in ('5', '6'): # SHA-2

if rounds is not None:

if not 1000 <= rounds <= 999_999_999:

raise ValueError('rounds out of the range 1000 to 999_999_999')

s += f'rounds={rounds}$'

elif rounds is not None:

raise ValueError(f"{method} doesn't support the rounds argument")

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

methods = []

def _add_method(name, *args, rounds=None):

method = _Method(name, *args)

globals()['METHOD_' + name] = method

salt = mksalt(method, rounds=rounds)

result = None

try:

result = crypt('', salt)

except OSError as e:

# Not all libc libraries support all encryption methods.

if e.errno == errno.EINVAL:

return False

raise

if result and len(result) == method.total_size:

methods.append(method)

return True

return False

_add_method('SHA512', '6', 16, 106)

_add_method('SHA256', '5', 16, 63)

# Choose the strongest supported version of Blowfish hashing.

# Early versions have flaws. Version 'a' fixes flaws of

# the initial implementation, 'b' fixes flaws of 'a'.

# 'y' is the same as 'b', for compatibility

# with openwall crypt_blowfish.

for _v in 'b', 'y', 'a', '':

if _add_method('BLOWFISH', '2' + _v, 22, 59 + len(_v), rounds=1<<4):

break

_add_method('MD5', '1', 8, 34)

_add_method('CRYPT', None, 2, 13)

del _v, _add_method

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