[Suicide Junkie]

As I understand it, they let the player use its personal key to decrypt the movie key.
Then they pick the movie key out of memory and use it to decrypt the movie.

Each player has a key... which all lead to the master movie key, which gives you the movie.
Player keys can be revoked, but if nobody knows which player key was compromised, the only remaining option is to revoke them all, give up, or continue to sue all your customers.