If you can see it, you can copy it. When it comes to anti-piracy methods in cinema, this is an inescapable fact. Digital cinema takes great care to ensure that the light emanating from the lens is the only opportunity for stealing the movie. This report provides an overview of the methods employed in cinema to limit content theft.
Most readers are aware that a Key Delivery Message (KDM) is needed to decrypt a movie on a particular media block. The DCP consists of many files, each file representing one type of essence, such as picture, sound, or subtitles. Further, the essence files are temporal in nature, meaning that each file typically contains only a time-slice of the movie. To provide some organization to the collection of files, the same time-slice is applied to each essence type. We call each time-slice a “reel,” as in a reel of film, the analog of the time-slice concept.
The content owner has the option to encrypt the files of its choice. Typically, all of the files will be encrypted. Each file is encrypted using a unique symmetrical key. Symmetrical means that the key that encrypts the content is also the same key that can be used to decrypt it. The collection of symmetrical keys are then encrypted using an asymmetrical key called a “public” key. With asymmetrical encryption, two keys are employed to encrypt and decrypt, typically called “private” and “public” keys. In the digital cinema case, the public key of the media block’s digital cinema certificate is used to encrypt the symmetrical content keys. Only the private key of the media block can then be used to unlock the symmetrical keys. Once unlocked, the exposed symmetrical keys can be used to decrypt the content for playout. The unlocking of keys in the KDM and the unlocking of the movie itself are performed in the secure processing block within the media block. The secure processing block is tamperproof. An attempt to break into its perimeter will cause erasure of the digital cinema certificate private key and any exposed symmetrical content keys. As one can see, this is a very tight security system. Anyone interested in stealing the movie will expend a lot less effort using a camcorder to steal the light that comes out of the projection lens and onto the screen.
One may be able to steal light from the lens, but not without risking detection. The image and sound captured by a camcorder will be forensically marked with the time of day and the identity of the media block used to play the stolen content. Content owners, upon discovery of pirated copies of their movies, decode the forensic mark and turn over the information to investigators. The investigators then apply other forensic science techniques as they carry out the criminal investigation.
First release motion pictures are highly valued, and the security of this content in digital cinema is taken very seriously. Strong encryption and security management techniques are applied to ensure that digital files cannot be copied. The only way left to steal a movie is the camcorder, but forensic marks will not allow one to do so imperceptibly.