Why use pack at all? Try this:

use Crypt::CBC;
use Storable qw(freeze thaw);
use MIME::Base64 qw(encode_base64 decode_base64);

my $priv_key = "fdslgjlsdgjl flds";
my $encrypt_method = "Crypt::Blowfish";

my $cipher = new Crypt::CBC($priv_key,$encrypt_method);

sub save {
  my $data = shift; #data struct you want to save
  return encode_base64($cipher->encrypt(freeze($data)),"");
}

sub reload {
 my $string = shift; #string you got back from form
  return thaw($cipher->decrypt(decode_base64($string)));
}
[download]

I use this to preserve the state in a cookie typically, but you could also pass it along in a form. If you want to pass it in the uri you need to translate some chars (I don't remember which ones though).