Bullet versus armour
In the age of content you can forget the concept of protected content. The bullet wins always the race with armour. And so the cracker wins always against a protection scheme: Decryption Keys For HD-DVD Found, Confirmed. When you give up the control about the deciphering key, it´s almost sure, that someone finds a way to gather the or a key and thus breaks your encryption scheme. You can make it harder, but not impossible. And a single key is a homerun against all existing titles on the market.