no slogan's criticism is correct. You should probably error out if the pad is too short to effectively cover the entire raw text. Otherwise you lose the whole benefit of having a one time pad.

Almost, and maybe even more important, is that you have some Perl 4 idioms scattered throughout your script-- especially in the CGI-specific areas. Maybe you've been reading some older editions for examples of good ways to do stuff. You should definitely use the CGI.pm module to accept and parse the form data. It also makes a nice touch to use the CGI.pm to produce your HTML-- especially for making forms, since it excels at that sort of thing.