well; then you just have to change print $result; with $_ = $result; I suppose... But i don't know how the $_ variable is handled with packages (yeah it's my first one) so, if you could tell me if it's the right way to re use the encrypted string...
Er... no. return $result; Then, caller could do (after importing the functions) $ciphertext = acrypt($plaintext, $key); (or similarly for adecrypt). See perlvar, perlmod, perlsub.