I completely agree with tachyon's and Abigail-II's responses. So, if you haven't already, first implement your protection via htaccess or whichever security measure your webserver provides. However, if afterwards you want to learn a little about security...try using cookies (they're fun).
I have seen a great cookie module written by eresei that implements blowfish encryption to provide security to several protected web utilities. BTW, there are several accepted ciphers to the Crypt module, not just blowfish. So again, after you get htaccess (or similar) protection set up...you may want to study up on some encryption schemes and try using cookies. You'll probably better understand security and security related issues/concerns, and you'll learn a new subset of Perl.
Chris

Update: Sory for the misspell erasei