It is close to your first thought. I sort of did a design mistake having (rot13): n yrsg, zvqqyr, naq evtug frpgvba gb gur wryylsvfu ebbz jura gung'f abg npghnyyl eryrinag gb gur chmmyr. Gur eryrinag cneg vf gur zvffvat yvzof bs gur wryylsvfu gung ner ba gbc bs rnpu ahzore, abg jurer rnpu ahzore vf ybpngrq.