Good use of unpack and ord, but watch out for things that generate warnings. Some people will disagree with me, but I think that even obfuscated code should avoid warnings:

%perl -w japh.pl
Use of uninitialized value at japh.pl line 3.
Use of uninitialized value at japh.pl line 3.
Just another Perl hacker

BTW: the warning is from the $i in the while loop. If you add some garbage to shift your array (so that you can start from 1 instead of 0) you could preincrement $i just before your loop, or hide your initialization somewhere.Maybe monkey with $[