Introduction
In November 2005 the Digital Video Broadcasting Project published a Blue Book, A094, containing the first three elements of its specification for a Content Protection & Copy Management (DVB-CPCM) system for use in consumer digital products and home networks.

The first three elements of the DVB-CPCM specification are: the CPCM Reference Model, which provides a technical and architectural framework for the CPCM System; the CPCM Usage State Information, which is content metadata that signals the authorised usage for a particular Content Item; and CPCM Abbreviations, Definitions and Terms.

Although the full system specification for CPCM is not complete the Blue Book is published for informational purposes and liaison with other interested standards forums. When completed the DVB-CPCM specification will be submitted to ETSI for standardisation.

This article will not go into a detailed description of the full functionality offered by DVB CPCM as the reader can obtain the Blue Book by download from the DVB web site (DVB 2005). Rather the following is intended to give background to the DVB, why it embarked upon the work, and the major concepts embodied within the specification.

About the DVB
Today, the Digital Video Broadcasting Project (DVB) is an industry-led consortium of approximately 300 broadcasters, manufacturers, network operators, software developers, regulatory bodies and others committed to designing open standards for the delivery of digital television and data services. Although based in Europe DVB has members in over 35 countries.

The genesis of DVB was the debacle following the market failure in the early 1990’s of the D-Mac satellite system which was mandated by the EC administration but not supported industry wide in Europe.

Persisting in the belief that pan-European standards for digital broadcasting will bring major benefits to consumers and manufacturers, the European Community administration turned to the industry and encouraged the setting up of a cross industry group to produce open specifications for standardisation based on industry consensus. This led to the formation of the DVB Project in 1993.

Initially the DVB concentrated on producing specifications for digital transmission systems for satellite, cable and terrestrial delivery and an interoperable Conditional Access system. These specifications have been adopted on a world wide basis resulting in the DVB becoming accepted as one of the leading specifications bodies. In recent times DVB has moved into the area of middleware and software producing the Multimedia Home Platform specification for interactive content and the Portable Content Format to provide common authoring to non-interoperable interactive platforms. Recently completed specifications also include DVB-H for broadcast delivery to hand held devices, DVB S-2 an updated and more efficient system for satellite delivery than its first specification which is now ten years old. Work is ongoing within DVB on advanced encoding technologies and IPTV.

Since its inception the DVB Project has proven the value and viability of pre-competitive cooperation in the development of open digital television standards. DVB open standards guarantee fair, reasonable and non-discriminatory terms and conditions with regard to Intellectual Property Rights, allowing them to be freely adopted and utilised worldwide. Open standards guarantee that compliant systems will be able to work together, independent of which manufacturer provides the equipment enabling considerable economies of scale to the benefit of the industry and also the consuming public.

The DVB is market lead. Its technical specifications are written to strict commercial requirements established by consensus by its members which represent all the industry constituencies of interest and the consumer through CE and IT vendors and broadcasters who have an interest in only producing products which are compelling and affordable.

Why DVB CPCM?
In the late 1990’s visionaries in the DVB predicted that the future growth of digital distribution of video and audio content; the advent of affordable consumer digital recording and processing equipment and software; and the potential for easy content movement by peer-to-peer transfer via broadband connectivity, would turn the existing consumer content usage paradigm on its head. Whilst convenient for consumers, the ease of unrestricted re-distribution of commercial content and associated loss of revenue to the content creation industry would reduce the income needed for investment in new content. The inevitable reaction of the content industry would be the push for DRM and content protection technologies in consumer products. On the other hand, a degree of content usage control, where applicable, would encourage content providers and distributors to introduce compelling new consumer propositions enhancing digital home networking and storage.

It was therefore logical that DVB should embark upon an attempt to produce a specification for digital content protection and copy management to complement its other work in emerging new platforms. Interested DVB members determined to attempt to provide an open standard CPCM system specification for use in consumer products which, if adopted, will avoid a plethora of non-interoperable proprietary systems resulting in higher costs and consumer confusion so slowing digital take up and hindering moves towards analogue switch-over.

In September 1999 the DVB established a new commercial sub-group within its Commercial Module with a mandate to prepare Commercial Requirements for a CPCM system to provide a common framework for the protection and management of commercial content in consumer digital equipment and home networks whilst taking into account consumer interests such as; no requirement for system registration or a return path; simple to use with clearly displayed information about usage rights.

The group spent three years deriving the Commercial Requirements for CPCM which indicates the degree of difficulty in reaching consensus across the industry in the emotive area of content protection.

Inevitably viewpoints were initially somewhat polarised across the industry sectors. For example, there was clearly a need to balance the concerns of the rights owners to protect their revenues with the concerns of the consumer electronics industry to protect the investment made by their customers in purchasing equipment. Public Service broadcasters were concerned that signalling over restrictive use of their broadcast content would conflict with their public service charters. Pay TV broadcasters were looking for a means to integrate CPCM with existing Conditional Access systems to support new commercial offers such as VoD (video on demand). However, despite these differences, consensus was finally achieved by participants recognising and accommodating each other’s business models.

In 2001 the Commercial Requirements for CPCM were approved by the Steering Board of the DVB and a sub group of the Technical Module was set to work to produce the specification.

The CPCM system
Although the functionality targeted for DVB-CPCM is much less ambitious than that of a full digital rights management (DRM) system, the scope envisaged is for end-to-end protection of commercial digital Content in all processes from the point of acquisition by the consumer through to the point of consumption. Possible sources of commercial digital Content include broadcast (e.g., cable, satellite, and terrestrial), Internet-based services, packaged media, and mobile services, among others.

It is also intended that DVB-CPCM shall be applicable to the widest range of equipment encompassing in-home digital networks, personal digital recorders; in the home and portable, and facilitate remote connectivity to other locations such as a second home or a vehicle.

CPCM is intended to be used to manage all types of commercial Content audio, video and associated applications and data delivered to consumer devices from acquisition until final consumption, or export from the CPCM system. Allowed usage is signalled by Usage State Information (USI) in the form of metadata which is securely bound to the content.

USI has been designed to accommodate a variety of business models and regulatory regimes. The existence of any particular field of USI in the specification does not imply that it will be asserted in a particular instance, or that it will be allowed to be asserted. Details regarding how and by whom a USI field can be asserted or changed will be reflected in the relevant CPCM compliance regime, which is outside the scope of the specification. For instance, European Public service broadcasters are indicating that they are considering setting a profile of CPCM USI signalling such that content scrambling should not be applied and that the only restriction required is to inhibit the re-transfer of the Content by means of the Internet.

CPCM is intended to interface with DVB Conditional Access (CA) systems and, where required, free-to-view broadcast delivery networks. It was recognised that DRM and copy protection systems already exist in the marketplace and will continue to be used and developed. Hence to the extent possible, without compromising its integrity and security, DVB-CPCM must co-exist with and interoperate with other DRM and copy protection systems.

The Authorised Domain
The DVB recognised that to conform with the traditional user experience of home recording, the portability of pre-recorded content, and expectations based on emerging digital connectivity, it was necessary to identify a mechanism to replicate the reasonable boundaries of content movement consumers have come to expect whilst not limiting the advantages of new digital technology. Based on the above, the concept of a user "Authorised Domain" was developed.

The Authorised Domain is defined as a distinguishable set of DVB CPCM compliant devices, which are owned, rented or otherwise controlled by members of a single household. A household is considered to be the social unit consisting of all individuals who live together, as occupants of the same domicile. This makes no assumptions about the physical locations of the devices owned, rented or otherwise controlled by the members of the household and no mechanisms to identify and/or authenticate the user shall be required.

A CPCM device may only be a member of one Authorised Domain at any time. When signalled by USI, Content is constrained to the Authorised Domain by which it is acquired and will not play on a devices belonging to a different Authorised Domain. However, to allow flexibility of connection a device can be re-assigned to another Authorised Domain for the purpose of consumption of Content assigned to that Domain during which time it cannot access Content which was bound to its original Authorised Domain. There is no limit to the number of times a device may move between Domains as long as the Content-to-Authorised Domain binding is maintained.

The specification provides mechanisms to determine the size and scope of the Authorised Domain; such size and scope to be decided by the implementer and possible local regulation.

DVB-CPCM can also be used to constrain Content to the local environment into which it is delivered by broadcast, if so signalled by the USI, to support local rights assigned to the broadcaster. The local restriction can be lifted after a defined period of time or the end of the transmission.

It should be emphasised again that provision of this mechanism does not mandate content distribution restriction in all cases. The USI will convey the restriction of movement within the Authorised Domain when it applies. If the restriction is not signalled by USI then the user will be allowed to send the content “outside” the Authorised Domain. It is envisaged that there will be many cases where the content owner or distributor will wish this to happen.

End-to-end protection & interoperability
A guiding principle in the development of CPCM is that implementation should not be dependant on a single technology. Rather, CPCM should provide a framework for interoperability between competing technologies. This enables a range of competing technology providers to collaborate to achieve a specification for a system which, whilst providing interoperable transfer of content between devices from a choice of providers, ensures that consumers can purchase equipment from different manufacturers in a competitive market and be assured that the equipment will inter-operate.

DVB-CPCM is intended for deployment in individual devices and in home networks. A content scrambling algorithm and secure exchange mechanism will be specified to preserve the security of the CPCM system. CPCM Content will only transfer between devices which are fully DVB-CPCM compliant, can establish mutual trust, and obey the USI. Intermediate devices, or entities such as network architecture items and storage on hard drives or removable recordable media, should be transparent because the Content and USI is secure. This approach increases security and ease of implementation by avoiding the necessity of multiple decrypt and re-encrypt processing as would be the case if each entity, device or linkage, comprising a home network was to use incompatible security mechanisms. It also reduces the need for multiple cross-licensing.

Next steps
The DVB Technical Module sub group is working to produce the specification for the security elements, to fully technically define the characteristics of the Authorised Domain, and the means to securely bind content within its boundaries. It is hoped that these final elements of the CPCM system specification will be published by mid-2006, along with Implementation Guidelines which will give examples of the use of CPCM in a number of markets and business models. Guidance will also be provided on the scope of technical testing required to ensure interoperability and compliance.

Cross industry support
Although CPCM is probably the most contentious work item the DVB has attempted the process has received input and support from, typically 25 to 30 member companies from across the industry constituencies of interest with representation from major technology providers.

Inevitably there is likely to be criticism, even from some DVB members, of the development of any form of content protection in consumer products and accusations that DVB CPCM will limit the availability of content to consumers. But the majority of DVB members believe there is a growing market need for content protection and copy management and that the DVB history of an inclusive, open consensus building approach provides the best option for development of a specification which will provide tools with wide ranging options.

Some critics have accused the DVB of conducting this work “behind closed doors”. Whilst it is true that the DVB is a member organisation, it is open to any organisation or company which wishes to participate and is willing to contribute its intellect or technology to the benefit of the industry at large. Membership requires the signing of the DVB Memorandum of Understanding which requires this commitment.

Sources
  • DVB (2005): Digital Video Broadcasting (DVB) Content Protection and Copy Management (CPCM) System. CPCM Reference Model. DVB Document A094, November 2005; http://www.dvb.org/index.php?id=294

Acknowledgement: This significant work which started five years ago has been supported by a broad representation of DVB members from all the constituencies of interest; content providers, broadcasters, distribution platform operators, consumer product manufacturers, and technology providers. As can be imagined content protection in consumer products and some free-to-air broadcast markets is a potentially contentious issue. It has therefore taken some time to embrace the concerns of all the players in the market and for all the parties to reach a level of understanding of each other’s present and future business models.

The author therefore acknowledges the work of all colleagues in the DVB commercial and technical sub-groups.

About the author: Chris Hibbert is Vice President Media Technologies & Standards with Walt Disney Television International. He was formerly Director of Engineering with ITV Digital in the UK during which time he became chairman of the DVB CPT group. Previously as Director of Engineering for the ITV Network he was responsible for technical strategy for DTT and was a member of the DVB group which wrote the requirements for the DVB-T specification. Hibbert is a member of the DVB Steering Board, has played an active role in the TV-Anytime Forum and is a fellow of the Royal Television Society. Contact: chris.hibbert@disney.com

Status: first posted 13/12/05; licensed under Creative Commons
URL: http://www.indicare.org/tiki-read_article.php?articleId=159