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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, *, 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 = crypt('', salt)
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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