chkpasswd

chkpasswd.c

#include <stdlib.h>
#include <unistd.h>
#include <crypt.h>
#include <stdio.h>
#include <shadow.h>

int main (int argc, char *argv[]) {
  char *plain_passwd;
  char *crypt_passwd;
  char *username;
  struct spwd *shadow;

  if (argc != 2) {
    exit(-1);
  }

  username = argv[1];
  plain_passwd = getpass("password:");

  if ((shadow = getspnam(username)) == NULL) {
    exit(-1);
  }

  crypt_passwd = shadow->sp_pwdp;

  exit(strcmp(crypt(plain_passwd, crypt_passwd), crypt_passwd));
}

Makefile

all: chkpasswd.c
        gcc -o chkpasswd -l crypt chkpasswd.c
install: all
        install -s -m 4755 chkpasswd /usr/local/bin