/*
 * modified by: G. D. LaBossiere, Xview Solutions Inc.
 * last modified: 2015-07-15
 * license: GNU GPL v3 <http://www.gnu.org/licenses/gpl-3.0.txt> 
 * comments: requires 2 parameters on the command line:
 * <password> (cannot be empty) <salt> (2 to 16 characters); returns a
 * sha512 encrypted hash in /etc/shadow format, i.e. $6$salt$password_hash
 * compile for your machine's arch:
 * /usr/bin/gcc -lcrypt -o passwd-sha512 passwd-sha512.c
 * to use an openssl-generated random salt:
 * passwd-sha512 "password_to_hash" "$(openssl rand -base64 16 | tr -d '+=' | head -c 16)"
 * adapted from http://serverfault.com/questions/330069/
*/

#define XOPEN_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  if ( argc < 3 || (int) strlen(argv[1]) < 1 || (int) strlen(argv[2]) < 2 || \
    (int) strlen(argv[2]) > 16 ) {
    printf("Usage:\t%s <password> <salt>\n", argv[0]);
    printf("\tPassword cannot be empty.");
    printf(" Salt must be from 2 to 16 characters.\n");
    return;
  }

  char salt[21];
  sprintf(salt, "$6$%s$", argv[2]);

  printf("%s\n", crypt((char*) argv[1], (char*) salt));
  return;
}