Linux Security Cookbook [Electronic resources]

Recipe 9.2 Testing Login Passwords (CrackLib)

9.2.1 Problem

You want assurance that your login passwords are secure.

9.2.2 Solution

Write a little program that calls the FascistCheck function from CrackLib:

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <crack.h>
#define DICTIONARY "/usr/lib/cracklib_dict"
int main(int argc, char *argv[]) {
char *password;
char *problem;
int status = 0;
printf("\nEnter an empty password or Ctrl-D to quit.\n");
while ((password = getpass("\nPassword: ")) != NULL && *password ) {
if ((problem = FascistCheck(password, DICTIONARY)) != NULL) {
printf("Bad password: %s.\n", problem);
status = 1;
} else {
printf("Good password!\n");
}
}
exit(status);
}

Compile and link it thusly:

$ gcc cracktest.c -lcrack -o cracktest

Run it (the passwords you type will not appear on the screen):

$ ./cracktest
Enter an empty password or Ctrl-D to quit.
Password: xyz
Bad password: it's WAY too short.
Password: elephant
Bad password: it is based on a dictionary word.
Password: kLu%ziF7
Good password!

9.2.3 Discussion

CrackLib is an offshoot of Alec Muffet's password cracker, Crack. It is designed to be embedded in other programs, and hence is provided only as a library (and dictionary). The FascistCheck function subjects a password to a variety of tests, to ensure that it is not vulnerable to guessing.

9.2.4 See Also

Learn more about CrackLib at http://www.crypticide.org/users/alecm.

Perl for System Administration (O'Reilly), section 10.5, shows how to make a Recipe 4.2]