Lights, Camera, Controls!

The possibility of one DVD spawning countless perfect digital copies is, for the movie industry, the scenario for the ultimate horror show

6 min read
Illustration: Marc Rosenthal
Illustration: Marc Rosenthal

Of all the forms of recorded entertainment, by far the most expensive to produce is the feature film. With costs sometimes exceeding US $100 million, movie studios play a high-stakes game and can't afford to lose revenue to large-scale piracy or even casual copying of movies among friends. The biggest fear is that consumers will not only copy DVDs, but also share them on the Internet.

For most of the history of the motion picture industry, piracy wasn't an issue; few had the means to view films outside a movie theater. That all changed with the 1976 introduction of home video recording. After a long legal battle between content owners and Sony Corp. (Tokyo), which had introduced its Betamax videocassette recorder (VCR), consumers had the right as well as the means to record copyrighted material on magnetic tape and use it in any way they saw fit—as long as that use wasn’t itself a copyright infringement, like making copies for sale or passing them around to friends [see “Extreme Lawsuits”].

But the VCR is an analog medium, recording signals by means of an electrical undulating, or analog, signal, that corresponds to the original, incoming signal. This fact imposed inherent limits on copying: copies were never as good as the originals, and quality degraded through multiple copy generations.

Still, the movie industry perceived any copying as a threat and looked for a way to protect the video signal emanating from the VCR. The means was at hand: video signals contain lots of unseen information required for display, such as sync, blanking, and color reference signals. These unseen components can be manipulated to prevent copying with little disturbance to normal TV playback.

An effective method of analog video signal protection that is used on nearly all video home system (VHS) movie releases to this day was developed by Macrovision Corp. (Santa Clara, Calif.). Various small companies released low-cost “Macrovision stoppers,” but they never caught on with the general public. The U.S. Digital Millennium Copyright Act of 1998 makes such devices illegal, but they can still be easily obtained.

Then came DVD

The DVD was introduced to the U.S. market in 1997, some 20 years after the Betamax. In two years, it became the most quickly accepted consumer electronics product in history. Storing movies in digital form, DVDs offer vastly superior picture quality compared to tape, and theater-quality sound. Like CDs, they potentially allow unlimited copying with no degradation from one generation to the next.

Movie studios feared DVDs could destroy their business and resisted releasing movies in the new format, stalling the introduction for over a year while the technology was altered to protect the content. The encryption system adopted to prevent copying was the content scramble system (CSS). With CSS in place, home copying of DVDs was curtailed, but in October 1999 the DVD world changed dramatically. A 16-year-old Norwegian programmer, Jon Johanssen, created a software utility he called DeCSS, which broke the CSS scrambling and allowed the reading of encrypted DVDs.

When Johanssen posted the DeCSS code on the Internet, the movie industry reeled. CSS, the linchpin behind DVD security, could now be unlocked by

virtually anyone. The legal battle that followed hinged on the controversial stipulation in the Digital Millennium Copyright Act that any method created to circumvent a publisher’s copyright control technology was illegal. The case was decided in the studios’ favor. With that decision, all links to the DeCSS code were forced off the Internet, and the CSS system continues to curtail casual home copying.

Nonetheless, DeCSS is still around, and though it requires some technical expertise to apply, the studios are not happy about it. Adding to their concerns is the proliferation of DVD-recordable drives in desktop and even laptop computers, and the new stand-alone (non-computer) DVD recorders already on the market and likely to become quite popular in the next year or two.

Watermarking fingerprints

So several approaches beyond CSS for preventing the copying of $30 DVDs to $1 blank discs are being considered. Some of these mechanisms block copies from being made in the first place, others stop the playback of copies after the fact.

As with copying from a VCR, the DVD’s signal can be transferred to a blank DVD, VHS tape, or computer hard drive via the analog outputs going from the DVD player to the television set, but with much less degradation than that seen with analog videotape. Macrovision’s technology will stop such copying, but is not hard to circumvent.

The most viable proposal for thwarting analog copying is watermarking, in which an invisible “fingerprint” of digital data is encoded into each of the movie frames. The watermark remains machine-detectable after analog copying. When a recording device designed to support this form of copy protection detects the watermark, it may refuse to record the content. And, if such watermarked content is recorded onto a blank disc by a rogue recorder, future players, which will look for watermarks, could still recognize that the disc is a recordable type rather than a pressed DVD, and refuse to play it.

As an added benefit, home movies transferred from a camcorder would be unaffected. But films captured by a camcorder in movie theaters would be stopped cold, thanks to the watermarks in the images picked up by the camcorder. (Though producing inferior images, such copying is a major source of pirated movies.)

Behind the Scenes:

The Copy Protection Group

  1. When DVD technology was developed in the mid-1990s by a consortium of 10 companies, the initial plan to protect digital discs was simple: to employ the same system being used to protect the analog output of VHS tapes, the one produced by Macrovision Corp. (Santa Clara, Calif.). While the movie industry favored the plan, the information technology industry opposed it because of how long it took to make a PC check for Macrovision pulses on every video frame.

    No other protection scheme existed, however, and time was crucial because the bits on the disc itself could easily be copied from the DVD drive of a PC and used to make an unlimited number of perfect copies, a possibility that terrified content owners.

    In early 1996, accordingly, the Copy Protection Technical Working Group was formed to explore techniques for protecting DVD content. The group was composed of members of the Motion Picture Association of America (MPAA), the Information Technology Industry Council (ITIC), the Consumer Electronics Association (CEA), and the Recording Industry Association of America (RIAA), as well as law firms and technology watchdog organizations.

    That year in June, a technology intended to prevent direct digital copying, called the content scramble system (CSS), was proposed by Toshiba Corp. (Tokyo) and Matsushita Electric Industrial Co. (Osaka, Japan). CSS was quickly adopted and is on all DVDs and DVD players sold today.

    But in 1999, a Norwegian teenager struck a devastating blow when he posted a CSS-cracking program called DeCSS on the Web. The software, which decrypted DVD movies into raw, copyable data, was widely distributed.

    Recognizing that analog signals also must be protected, the working group has for the last six years been exploring watermarking technology. But watermarking has proven to be a complex issue, and, despite many tests, the group has not yet decided on a single technique. Two proposals are being evaluated by the watermark group, composed of Digimarc, Hitachi, Macrovision, NEC, Philips, Pioneer, Sony, and Toshiba.

    These propose longer encryption keys for protecting both recordable and pre-recorded media. (At the time of its development, because of restrictions under import-export controls, the key length was limited to at most 40 bits.) One strategy increases the key length to 56 bits, making the key harder to break.

    New technology introduced by the group includes the media key block. This makes it possible to revoke compromised keys separately and without damage to the total encryption system. Another technique is actually an off-disc scheme, a transmission line protection system called digital transmission content protection.

    In finalizing the copy protection technology, group members must compare the cost of implementation with its effectiveness in blocking copying. Still, it is difficult to reach a consensus.

    —Hisashi Yamada

Watermarking, which can prevent both analog and digital copying, involves tradeoffs affecting the visibility of the watermark, its ability to withstand attack, and cost of implementation. But it works, and the copy protection technical working group has, after six years, narrowed the list of viable systems to two [see “Behind the Scenes”]. Such content already exists (the BBC has watermarked some of its shows and movies for quite a while), but current recorders, players, and computer DVD drives do not look for watermarks. Once a standard is implemented, new DVD players will be able to control the playback of watermarked content.

But what’s to stop a true pirate from pressing thousands of nonrecordable DVDs, making bit-by-bit copies? To block a pressed bit-copy from playing, the player must tell the difference between authorized and unauthorized discs. So authorized DVDs must include some feature nearly impossible for pirates to duplicate.

In the groove

Royal Philips Electronics NV (Amsterdam, the Netherlands) is promoting “disc wobble” (also called wobble groove) technology as a solution. This technique encodes hidden protection data onto the lead-in groove along the inner edge of a DVD in a difficult-to-duplicate manner. Normally, a DVD’s grooves form a smooth spiral, with the data encoded as reflective and absorptive spots along the path. Disc wobble reshapes the groove by wiggling the path back and forth ever so slightly in a pattern that conveys the ons and offs of digital data.

The wobble is too fast for the laser pickup head to physically follow, but the error signals that keep the head’s lens on track move in step with the wobble. This allows the protection data to be read by an appropriately equipped player, entirely separate from the normal movie data recorded in the track. If a decryption or authentication key is encoded in the wobble, devices that use this technology will play only wobbled discs. Used in conjunction with watermarking, disc wobble could ensure that watermarked content would be played only from wobbled—that is, authentic—DVDs. And because of the sophisticated tools needed to manufacture such discs, pirating wobbled discs would be next to impossible, at least for now.

Will such technologies stop DVD copying so that movies cannot be as easily traded as digital music files? Protection measures can, and probably will, be quite effective once today’s DVD players are replaced with a new generation of machines that respects these proposed forms of copy protection. Today’s DVD players will become obsolete if and when these new measures are encoded on all DVDs.

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