Blu-ray makes unexpected, three-way DRM choice for high-def DVD

Scott M Fulton III

August 10, 2005 - 13:18 EST

Hollywood (CA) - In an announcement last night, the Blu-ray Disc Association, led by Sony, representing one of two competing high-definition DVD formats, stated it will simultaneously embrace digital watermarking, programmable cryptography, and a self-destruct code for Blu-ray disc players.

The BDA statement is unprecedented not only because its solution to the nagging problem of digital rights management is to embrace every option on the table, but also because Blu-ray appears to have developed its own approach--in some cases, proprietary--to each of these three technologies. Knowledge of this impending fact may have been what tipped movie studio 20th Century-Fox last week to throw its support behind Blu-ray, in a move that experts believe balanced the scales in Blu-ray' s ongoing battle with competing format HD DVD--backed by a forum led by Toshiba--to become the next high-def industry standard.


The digital watermarking technique, which will be called ROM Mark, is described in the statement as " a unique and undetectable identifier in pre-recorded BD-ROM media such as movies, music and games." " BD-ROM" is the proposed writable version of the Blu-ray format. Little else is known about ROM Mark at this time, except that the statement describes it as being undetectable to consumers. This is noteworthy in itself, since a previously heralded watermark applied to first-generation DVDs was notoriously defeated by someone writing over it with a permanent marker.

One part of the announcement that had been anticipated by experts was Blu-ray' s embrace of Advanced Access Content System (AACS), one version of which has also been adopted by the HD DVD Forum. This controversial technology would require that disc players maintain permanent connections to content providers via the Internet, making it possible for discs that fail a security check to trigger a notification process, enabling the provider to send the player a sort of " self-destruct code." This code would come in the form of a flash ROM " update" that would actually render the player useless, perhaps unless and until it is taken to a repair shop for reprogramming. The Blu-ray statement noted that certain elements of AACS have yet to be formally approved by the BDA.

The third part of the announcement that is perhaps most surprising, is Blu-ray' s adoption of a third DRM technique that appears to embrace some of the ideals of one of the technologies that had been considered, without actually licensing its methodology or its existing tools. The BDA statement introduces what it calls " BD+," described as " a Blu-ray Disc specific programmable renewability enhancement that gives content providers an additional means to respond to organized attacks on the security system by allowing dynamic updates of compromised code."

BD+ appears to be Blu-ray' s version of a concept previously under consideration called SPDC, which enabled the method for encrypting a disc' s contents to be included on the disc, rather than on the EPROMs of the disc player. One of the perceived failures of first-generation DVD was that its encryption mechanism of choice, called Content Scramble System (CSS), was spectacularly defeated, with the result being that the industry was forced to permanently and irreversibly support a now-worthless encryption scheme. With SPDC, new encryption algorithms could be adopted as old ones are cracked, enabling successive generations of high-def DVD to be stronger than earlier ones.

Two months ago, the HD DVD Forum considered a coupling of AACS with SPDC. But a scientifically accurate though politically imbalanced white paper released by the creators of SPDC technology, Cryptography Research, Inc. (CRI), soundly rebuked alternative DRM technologies, and thus may have unintentionally played a role in SPDC' s falling out of favor with the original supporters of CSS, some of whom were HD DVD Forum members. The Forum rejected " AACS+SPDC" for undisclosed reasons, leading many to speculate that Blu ray would respond by embracing SPDC.

However, as SPDC was originally discussed, there would only have been one encryption standard in use throughout the industry at any one time. According to yesterday evening' s BDA statement, BD+ would follow SPDC' s core principle, but instead allow each content provider to utilize whatever encryption standard it sees fit at the time. " With these enhancements," the statement reads, " content providers have a number of methods to choose from to combat hacks on Blu-ray players. Moreover, BD+ affects only players that have been attacked, as opposed to those that are vulnerable but haven' t been attacked and therefore continue to operate properly."

This last sentence is important, because one key objection that experts raised to the pairing of AACS with SPDC was the possibility that, once the single SPDC encryption scheme was broken, AACS could trigger a signal to all players using that encryption scheme, rendering all discs that use this scheme unplayable, perhaps prior to a system upgrade. The BDA statement appears to distance itself from the CRI approach to SPDC, perhaps to calm consumer fears that entire libraries of perfectly legitimate content could be rendered useless due to someone else' s illicit activities.

The CRI white paper, incidentally, distinguished SPDC by contrasting it with other DRM techniques such as watermarking. " Although some progress is being made at improving robustness and efficiency," the white paper states, " we are not optimistic that a practical and secure public watermarking scheme is possible." Such comparisons may have worked against SPDC' s eventual adoption by Blu-ray in method as well as in principle.

On behalf of the HD DVD Forum this morning, Toshiba' s advisor to the Forum, Mark Knox, released a brief statement: " Today' s announcement by the BD Group should not confuse anyone," states Knox. " HD DVD' s content protection system provides the highest level of advanced copy protection to meet content owner' s needs and the rigors of consumer demand." Knox goes on to say that AACS--which now singularly forms the crux of HD DVD' s DRM--is the most advanced such scheme yet devised, and that HD DVD' s own membership continues to back that approach.

" We will continue to promote further penetration of the format," Knox added, " while simultaneously seeking ways to eventually realize a single format that delivers optimized benefits to all concerned industries and, most important, to consumers."

Tom' s Hardware Guide will present an in-depth analysis of the Blu-ray/HD DVD format combat Thursday morning in its Business Reports section. There, we' ll speak with industry experts, including one prominent media pioneer, in examining how the participants in this struggle may actually have always been planning for its eventual resolution, and what form the fruits of that resolution may take.