to go from deck_{a1,b1} to deck_{a2,b1} you need to remove the encryption. In order to remove E(k_{a1}, ?), you need to know which one was used, but can't, beca

to go from deck_{a1,b1} to deck_{a2,b1} you need to remove the encryption. In order to remove E(k_{a1}, ?), you need to know which one was used, but can't, because it was shuffled. If you were able to know which one was used, you would know which card it was.