Create crypt(3) passwords with Python >= 3.13

crypt.py

#!/usr/bin/env python
#
# Copyright 2026 Christian Franke <nobody@nowhere.ws>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# This small script was created as Python 3.13 dropped the crypt module and
# Python is my ad-hoc way to call the crypt(3) function of the OS.
#
# The script can either be imported as module, then it exposes the crypt
# and crypt_gensalt methods of the underlying OS.
#
# It can also be executed directly, in this case, it will either take a password
# passed as argument or one provided interactively and hash it.
#


import cffi
import getpass
import os
import sys


_ffi = cffi.FFI()
_ffi.cdef("char *crypt(const char *phrase, const char *setting);")
_ffi.cdef("char *crypt_gensalt(const char *prefix, unsigned long count, const char *rbytes, int nrbytes);")

_crypt = _ffi.dlopen("crypt")


def crypt(phrase, setting=None):
    if hasattr(phrase, "encode"):
        phrase = phrase.encode('utf8')
    if hasattr(setting, "encode"):
        setting = setting.encode('ascii')
    rv = _crypt.crypt(phrase, setting)
    if rv == _ffi.NULL:
        raise OSError(_ffi.errno, os.strerror(_ffi.errno))
    return _ffi.string(rv).decode('ascii')


def crypt_gensalt(prefix, count):
    if hasattr(prefix, "encode"):
        prefix = prefix.encode('ascii')
    if prefix is None:
        prefix = _ffi.NULL
    rv = _crypt.crypt_gensalt(prefix, count, _ffi.NULL, 0)
    if rv == _ffi.NULL:
        raise OSError(_ffi.errno, os.strerror(_ffi.errno))
    return _ffi.string(rv).decode('ascii')


if __name__ == '__main__':
    if len(sys.argv) == 2:
        password = sys.argv[1]
    else:
        password = getpass.getpass()

    print(crypt(password, crypt_gensalt("$6$", 65536)))