The point was that you can either make the binding cost no computational resources for the reader (by publishing and the binding in plaintext), or you can make it cost some mild amount of computational power (say, put it in a list of 20 fake numbers), or you could make it computationally infeasible by encrypting it. Is the second option illegal? At what computational difficulty does it become illegal?

Either way, the fact that the third is legal means that the law depends on compute power.