Internet Programming w/JAVA

CS Account Verification

Using getpwnam()

The C library provides a function called pwnam(string name) which searches through the /etc/passwd (or its NIS equiv. in the case of CS) for the given username. It returns all information contained in /etc/passwd for that user. In PERL, the same function exists and returns an array containing the following:

login (login name)
passwd (crypted password)
uid (user id)
gid (group id)
age (unused)
comment (unused)
gecos (real name This is what we want!)
dir (home directory)
shell (login shell)

The verify_vote subroutine below demonstrates usage of getpwnam():

#######
## int verify_vote( login_name, last_name )  !! login_name is case sensitive
##                                           !! side effect: sets $reason
#######
sub verify_vote {
    local($id, $lastname) = @_;
    local($name, $passwd, $uid, $age,
          $comment, $gecos, $dir, $shell) = getpwnam($id);

    if(!$name) {
        $reason = "No such account";
        return 0;
    } elsif($gecos =~ /\b$lastname/i) {
        return 1;
    }
    $reason = "Your account status could not be verified. "
            . "Check last name and/or username."
    return 0;
}

Advantages

Fast! (spawns no external processes; no fork/exec overhead)
Small (after assignments it's only two if statements)

Disadvantages

User must have account on CS
Script MUST run on CS
Still not an ABSOLUTE verification

Andrew T. Graham (atgraham@cs.millersv.edu)
URL: http://cs.millersv.edu/~atgraham/vote/getpwnam.html