January 1, 2007
Studios’ DVDs Face a Crack in Security
By JOHN MARKOFF
SAN FRANCISCO, Dec. 31 — An anonymous computer programmer may have skewed the competition over standards for high-definition DVD discs by possibly defeating a scheme that both sides use to protect digital content.

The standards, HD-DVD and Blu-ray, are being backed by rival coalitions of Hollywood studios and consumer electronics and computer companies that are eagerly marketing a new generation of digital media players and video game machines tailored for widescreen TVs.

The HD-DVD coalition includes companies like Microsoft, Intel, Toshiba and NEC; the Blu-ray camp has Sony, Philips and Samsung. Among studios, Universal is exclusively backing HD-DVD. Paramount and Warner Brothers also support HD-DVD, but not exclusively. Representatives of Walt Disney, 20th Century Fox and Warner Brothers are on the board of the Blu-ray group.

The two groups have taken different technical approaches in their efforts to prohibit consumers from making copies of movies and other digital material stored on discs. Both groups use an encryption scheme known as Advanced Access Copy System. The Blu-ray system also adds a software-based component that makes it possible to modify the copy protection scheme on new discs if the old one is broken by hackers.

The standards are brand new, but it appears that the two groups’ copy protection schemes are already about to be tested.

The HD-DVD camp may have suffered a setback when the programmer, who identified himself as Muslix64, announced in the Internet discussion forum Doom9 on Dec. 18 that he had successfully copied movies distributed in the HD-DVD format. The note directed readers to a site where demonstration software he had written could be downloaded.

“I was not aware of anyone having done that, so I did,” he wrote.

In an accompanying video demonstration posted on the YouTube Web site, the programmer showed encryption keys for six movies and concluded by stating “A.A.C.S. is unbreakable? I don’t think so. Do you? Stay tuned for source code in January. Merry Christmas.”

For one thing, AACS wasn’t really cracked, as that term is commonly understood. Claims to the contrary are based on limited understanding of how AACS was designed to work.

For another, the compromise of a handful of titles now, while the number of discs and players in the market is still insignificant, provides a low-cost, low-risk opportunity to test how well AACS can respond to being compromised.

ACCORDING TO THE DOOM9 postings, Muslix64 was using the USB-enabled HD DVD add-on for his Xbox 360 to view HD DVD discs on his PC, using Cyberlink’s PowerDVD player software.

Using BackupHDDVD, he/she was apparently able to retrieve the title-specific decryption keys from the player memory during playback and then feed them into his/her own decryption procedure as outlined in the public documents available on the AACS Licensing Authority Web site.

The keys themselves apparently remain encrypted, however.

The basic approach with BackupHDDVD is not all that different from DeCSS, the first widely distributed crack of the CSS-encryption used on standard DVDs.

Like BackupHDDVD, DeCSS works by uncovering the decryption keys and using them to create unencrypted files on a hard drive.

In other important ways, however, there is a world of difference between the two scenarios, related to the designs of the respective encryption systems themselves.

CSS relied on a single set of keys that were used to encrypt every DVD and were provided to every DVD player, both hardware and software.

Once those keys were uncovered the first time, the system was fatally compromised. The same utility can be used to rip any DVD for all time.

AACS, on the other hand, was designed specifically to cope with the challenge presented by BackupHDDVD.

Both the PowerDVD player software and the titles themselves carry unique keys, which, if hacked, can be revoked. In principle, the damage can be limited to only those copies of Full Metal Jacket and the others currently in the market and to the PowerDVD player.

THE CHALLENGING PART will be getting the system to work as designed. And here, BackupHDDVD could be a blessing in disguise, giving the studios and software makers a chance to uncover potential bugs in the system while the numbers—and the potential damage—remain small.

First, additional forensic work will have to be done to determine exactly what BackupHDDVD does, to determine exactly where the compromise occurred.

If the player’s keys were indeed compromised, those keys could be “revoked,” meaning all discs pressed from that point forward would be unplayable in the cracked players.

That would have the effect of revoking the players of many people who had done nothing wrong, however, and would actually shield the guilty party or parties from having their players “updated” with new keys.

A more likely scenario is that the player’s existing keys would be revoked at the disc level. New copies of those titles would be replicated using new keys, so that the new discs would not play in the compromised players.

Updated keys for the PowerDVD player could then be distributed via new discs so that innocent owners of PowerDVD can continue to use their players.

How quickly that can all be made to happen, however, and with what degree of due-process for Cyberlink remain unclear. What procedures exist, exist only on paper and have never been tried in the real world.

But the studios might as well find out now, when the damage affects only a few catalog titles and a handful of players.

If the player’s keys were indeed compromised, those keys could be “revoked,” meaning all discs pressed from that point forward would be unplayable in the cracked players.

That would have the effect of revoking the players of many people who had done nothing wrong, however, and would actually shield the guilty party or parties from having their players “updated” with new keys.

A more likely scenario is that the player’s existing keys would be revoked at the disc level. New copies of those titles would be replicated using new keys, so that the new discs would not play in the compromised players.