I'm no expert on DCP or encryption. But from what I've read DCP uses AES 128, they probably didn't crack that. But also each projector gets its own unique key to decode the movie. Which I assume is somehow combined with the key in the projector to create the real decryption key.
So my first guess is that they had the ability to snoop on multiple key exchange messages and some how used that knowledge to find a shortcut to solve AES based on the gleaned knowledge from all the gathered keys, or they broke into a projector and took its internal key.
So my first guess is that they had the ability to snoop on multiple key exchange messages and some how used that knowledge to find a shortcut to solve AES based on the gleaned knowledge from all the gathered keys, or they broke into a projector and took its internal key.