manual/examples/genpass.c

   1 /* Encrypting Passwords
   2    Copyright (C) 1991-2023 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU General Public License
   6    as published by the Free Software Foundation; either version 2
   7    of the License, or (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <https://www.gnu.org/licenses/>.
  16 */
  17
  18 #include <stdio.h>
  19 #include <unistd.h>
  20 #include <crypt.h>
  21
  22 int
  23 main(void)
  24 {
  25   unsigned char ubytes[16];
  26   char salt[20];
  27   const char *const saltchars =
  28     "./0123456789ABCDEFGHIJKLMNOPQRST"
  29     "UVWXYZabcdefghijklmnopqrstuvwxyz";
  30   char *hash;
  31   int i;
  32
  33   /* Retrieve 16 unpredictable bytes from the operating system.  */
  34   if (getentropy (ubytes, sizeof ubytes))
  35     {
  36       perror ("getentropy");
  37       return 1;
  38     }
  39
  40   /* Use them to fill in the salt string.  */
  41   salt[0] = '$';
  42   salt[1] = '5'; /* SHA-256 */
  43   salt[2] = '$';
  44   for (i = 0; i < 16; i++)
  45     salt[3+i] = saltchars[ubytes[i] & 0x3f];
  46   salt[3+i] = '\0';
  47
  48   /* Read in the user's passphrase and hash it.  */
  49   hash = crypt (getpass ("Enter new passphrase: "), salt);
  50   if (!hash || hash[0] == '*')
  51     {
  52       perror ("crypt");
  53       return 1;
  54     }
  55
  56   /* Print the results.  */
  57   puts (hash);
  58   return 0;
  59 }