Chip safeguards 'pay-per-view' DVD discs

San Jose, CA--Before agreeing to release movies on Divx discs, Hollywood movie studios wanted some assurance that they'd be compensated for the content they created. A new chip from VLSI Technology has helped convince such giants as Disney, Paramount, and Universal to get behind the new DVD format.

Introduced at the January 1998 Consumer Electronics Show, the Divx system lets consumers purchase a Divx DVD disc for about $5--a fee that includes an initial, unlimited two-day viewing period that begins when the consumer inserts the disc into a Divx player and pushes the play button. After that, users pay a fee per play for additional viewings that is about equal to renting a videotape. For a larger charge, a user can authorize a disc for unlimited play.

Each time a disc is played, the Divx player stores its ID number in flash memory. An internal modem sends playback information to the Divx billing center twice daily, and users get a monthly bill.

The challenge? Make sure users couldn't watch Divx discs for free. Thus, all Divx discs are encrypted using triple DES encryption--the same system used in many military applications and which has received the strongest commercial ratings available. The discs and players are individually serialized, allowing the system to pass individual keys to Divx players and receive accountings from players on a disc-by-disc basis.

VLSI's security chip processes in real time the Divx player's encrypted digital video signal and playback code--the elements that prevent Divx discs from being played in standard DVD players. It also monitors any tampering with the player and automatically shuts the player down if it detects any tinkering.

"The DES algorithm is computationally intensive--it's doing a lot of complex math operations--and to do that to support a full-motion video data stream is no small undertaking," says Joe Wallace, a senior engineer with VLSI.

Why use hardware encryption instead of software, which is less expensive? "People start moving toward hardware when they need one of two things: speed or higher levels of security," says Wallace. "Divx requires both. The data rates were very high--it would have required practically the full bandwidth of a Pentium processor to run DES in software."

The Divx security chip is a custom design. But applications for VLSI security chips include other consumer applications that require fast decryption, such as cable modems and satellite receivers.

For added security, VLSI's chip uses an advanced protection technology from Dow Corning called ChipSeal(reg), which is designed to prevent breaking open the device to physically examine its circuitry and memory areas. This is the first commercial application of ChipSeal, says Wallace.