It has to be encrypted and decrypted by both Perl and Javascript.
What I'm doing is just implementing some minor encryption for transmitting form data back and forth from the browser. My only idea so far is to use xor (don't yell at me yet). I know that there's really no good way to do this, and I intend on telling the people who will be using this to only run it over a secure connection, but I'm realistic, so I'd like to put just a little extra security in there.