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Content protection in the digital century

Today subscription pay TV is common practice. It is well understood in the broadcasting world to lease consumers access to a protected pipe delivering content.

The digital television landscape has evolved considerably in the 10 years since services have been available to customers around the world. Where digital television is available, with some exceptions for digital terrestrial free to air services, it exists mainly on a subscription model, which favours the use of conditional access.

The cable and satellite platforms include so-called triple play (and the “quadruple play” — wireless enhanced) digital cable environments, local and distributed storage delivery models, personal video recorders, and the in-home or in-pocket store of detached content these create.

In the future, the most significant area where content protection is critical to business survival is the emerging market for Internet-based video services. There is pressure on DVD publishers to adopt certain technologies in order to release the rights, while at the same time concerted support for supporting various industry standards.

Major Hollywood content creators and providers, as well as international authors' societies, need to track and reconcile uses of their content. As a result, they have established many initiatives, from movie industry-led to those led by manufacturers such as Intel and other major IT and CE companies.

Content protection = copy protection + access control

Superficially, content protection appears to be an evolution of conditional access, the content security technology of pay television, typically found on a smart card or embedded in a set-top box. In fact, content protection is an entirely new application landscape, using similar technological elements, but quite different in the issues it raises.

The term content protection includes both copy protection and access control, two application areas fundamentally different in nature. Content may not be scrambled on air, but still carry copy protection signalling.

It is perfectly conceivable and a robust form of content security to use traditional conditional access where possible, and also to use copy and access control technology, which enhances functionality and usability in the authorised domain and prevents abuse of the rights appertaining to that content.

The DVB/EBU definition of copy protection states that: “A copy protection system is designed to signal the extent of allowed copying and serial copying, if any, that is defined by the associated ‘usage information’ with respect to any instance of delivered content, and to implement and enforce the signalled behaviour in consumer equipment.”

Copy protection defines usage states for content delivered across an open pipe, cloud or passed from one peer to another. Instead of the binary programme “entitlement” signalling of a conditional-access system for broadcast, one has a fluid set of different copy control rules. Copy once, copy never, etc.

The default copy protection state with which everyone, except users, is always comfortable with is “view once” (copy never), as in the days of live TV before even the VHS and Beta video recorders, and in the early days of HDTV, when it was still immature technology. Once, there simply was no way to copy something. Now there are many ways.

Content will be transported around by the authorised user in his authorised domain, for example, over an in-home digital network, or between his different devices. A user might wish and be entitled to make copies of content for personal use. For example, in a personal video recorder, such as a Tivo or a state-of-the-art set-top box with an embedded hard drive, content is coded onto the hard disk for later or repeated access.

The accepted terminology for these zones of copy control is domains. The DVB Project Copy Protection and Content Management (CPCM) has defined an interoperable broadcast system reference model and a domain model. This working group has been tracking copy protection and digital rights management technologies for six years.

Content protection includes effectively and indelibly tagging media files or streams, flagging or inserting metadata, and tracking it across its uses. Each time media is accessed in its lifecycle, its content protection metadata will be consulted by devices or applications.

By its nature, rights management requires access to commercially sensitive information (in opposition to copy information and usage signalling).

Copy protection and an access control method intrinsic to the content itself is a sine qua non without which digital rights management systems will not function. Copy protection is not only about preventing access but also about content management, enabling certain “authorised” patterns of access.

Figure 1. The DVB CPCM architectural model. Click here to see an enlarged diagram.

DVB has defined an architecture where standards-based and proprietary DRM technologies, incorporating copy control and access control technologies, can interoperate. (See Figure 1.)

Digital rights management

Digital rights management (DRM) covers the processing of rights information for the electronic administration of rights, including content tracking and financial recovery. By its nature, rights management requires access to commercially sensitive information (unlike copy control and usage signalling).

An important technology for rights management is the MPEG rights expression language. XrML XrML is an XML-based usage grammar for specifying rights and conditions to control the access to digital content and services. XrML began with Xerox. It was submitted by Xerox-affiliated Content-Guard and adopted by MPEG as part of MPEG-21.

DRM systems are still evolving, but there are considerable technological challenges, leaving some important gaps in coverage and protection in state of the art systems.

Thus, commercially used DRM has not yet reached a market-wide critical mass. Nevertheless, the IT world has made extensive use of DRM in protecting its computer programs and video games, and it is being used in several online music services, such as Apple's iTunes.

Several small IPTV projects are starting to use available DRM platforms, such as the pilot public IPTV service launched in Switzerland by Microsoft and Swisscom. This last service uses the proprietary Microsoft “Janus” DRM system in conjunction with a proprietary “streaming” video format, Windows Media Video (WMV).

Perhaps the reason why purists insist on distinguishing between copy control and access control is because there is no 100-percent perfect access control technology. Notwithstanding the security claims by proprietary DRM system vendors, there is always a level of risk. The goal is to keep it calculated and minimal. There are major gaps in technological protection of audiovisual content for broadcasting — anything that can be viewed by the human eye at acceptable quality levels can be simply copied.

Martin Jacklin is a technology writer and principal consultant at Broadcast projects (