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We have to use what we have available, and we know we can call on getDocumentBase() for help.

What can be done to stop the majority of these thefts? Well, we have to use what we have available, and we know we can call on getDocumentBase() for help. This method comes from the Class Applet, in the package java.applet. The method getDocumentBase() tells you where the HTML page was served from. Using getDocumentBase(), one can determine the page's origin, and if we call these methods from within the applet, we can prevent it from working if it's not coming from the correct server. Here's a simple applet showing how it works:

import java.net.*;
import java.applet.*;

public class stopthief extends Applet {

public void init() {
String stolen;
Stringowner =
getDocumentBase().getHost();
if (owner.equals("www.yourdomain.com")) {
// this is where you would insert 
// your stuff for legit users
} else {
System.exit(1);  
// this is where you'll kill or 
// otherwise alter the applet for 
// thieves
}
}
}

What this does is to cause a security exception at System.exit(1) if the applet is not coming from your site. This is just an example, as you could cause it to do almost anything, but this way, it just won't work for thieves. One negative aspect of this method is that you'll have to change and recompile the applet if you change servers.

And just how secure is this method? Secure enough to thwart most applet thieves, but not enough to stop professionals, or even those with a lot of determination. How can they still make the applets function? Anyone familiar with a hex editor can tell you. There's no magic involved...just a little search and replace. So why implement the method at all then? Because it'll stop about ninety percent of those that would hack your applet, and the other ten percent will find a way to hack it anyway.

If you're not afraid to enter the world of CGI (and why would you be...you're already into programming enough to read this column), then you can create a CGI script that is called by the applet, and if the CGI doesn't pass the correct information to the applet, the applet will not function. Is it simple? Not particularly, but it is effective-more so than our previous example.

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