Well, you could store the number in a database table and associate it with user name or IP. This would eliminate the need to encrypt it and pass it from page to page. Or if the float number is part of a passcode or something and needs to be verified on every page, you could have the user log in, then use Digest::MD5 (a standard module included with Perl now - even MacPerl) to encrypt the user name or IP with a site key and then check that against the same thing generated on every successive page. If there isn't a match, the person didn't log in.

I wouldn't try encrypting something myself, though. Why spend time writing code that someone is bound to be able to break in five minutes?