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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]
