The context of the TIRAMISU framework
Convergence of digital media distribution channels and content representation formats has the potential to provide significant benefits to content owners and users alike by changing traditional content distribution and consumption patterns. Content that has initially been delivered over digital broadcasts can be further distributed over the Internet or through pervasive peer-to-peer (P2P) networks and consumed on a variety of consumption devices. Content providers are rapidly gaining awareness of the importance of multi-channel delivery of content, by which a potentially larger customer base can be targeted (Lauchlan 2001). At the current stage, content providers address each delivery channel independently of others by preparing content in a way that is specific for that channel. Protection methods that enforce consumption policies are also targeting specific requirements of a distribution channel. Opposed to this approach, multi-channel delivery allows preparing content for some display characteristics and content can be obtained either on, for example an IP network or a removable device. At consumption, if necessary, adaptation of content can be done. While multi-channel delivery has the potential to increase the owner’s revenue streams, content owners are becoming increasingly concerned in view of the innumerable possibilities for illegal consumption and distribution, P2P networks being the most highlighted threat.

Integration of DRM technology with alternative distribution channels such as P2P networks may provide the solution for crossing the fine line between embracing functionalities that users want and at the same time maintaining control over Intellectual Property Rights (IPR). A simplified DRM system (Figure 1) relies on media scrambling for protection. The privilege to consume protected content is granted to the end-user by a license, which specifies usage terms and conditions and includes the key(s) needed for content descrambling. The process of transferring scrambling keys between the content scrambling node and the rendering node is denoted by the term key management.

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Figure 1: Architecture of a generic DRM system.

Integration of media distribution and DRM is key to implementing content super-distribution. Super-distribution is an online retailing scheme that encourages free and widespread distribution of digital objects that can only be consumed under a restricted set of circumstances. Super-distribution is a distribution scheme where consumers are involved in the process of C2C (consumer to consumer) distribution of content initially acquired through B2C (business to consumer) distribution channels. For IPR protection reasons, content must be super-distributed in scrambled form. This implies the need for a DRM system that provides the means to acquire consumption rights and descrambling keys on one hand and enforcement of those rights on the other.

MPEG-21, which is the last in the series (MPEG-1,-2,-4,-7) of MPEG standards (cf. Burnett et al. 2003; Bormans and Hill 2002; Bormans et al. 2003) defines a normative open framework for interoperable multimedia delivery and consumption that is based on two essential concepts: the definition of a fundamental unit of distribution and transaction (the Digital Item - DI), and the concept of users interacting with DIs. A DI is a structured digital object with resources, unique identification and metadata, where the structure of the DI implies relationships among parts of the DI, i.e. the resources and metadata.

The TIRAMISU approach
The framework proposed by TIRAMISU is based on the MPEG-21 standard for multimedia content delivery and consumption and at the same time it complements it in several aspects, most notably by fully specifying a Digital Rights Management (DRM) scheme. Central to the described framework is a novel Key Management System (KMS), relying on smartcards, which addresses many issues that previously blocked wider adoption of DRM: obtrusiveness of the DRM technology perceived by the end user, flexibility in license formulation and adequate level of trust as requested by content owners. The TIRAMISU framework intrinsically supports the concept of super-distribution.

The central objective of the TIRAMISU project is to create an environment, in which content providers can deliver content to users over multiple distribution mechanisms to a variety of consumption devices, with confidence that imposed usage policies will be respected. At the same time TIRAMISU balances between insuring proper compensation to Intellectual Property (IP) owners and reasonable user expectations. TIRAMISU approaches this by motivating content distribution policies that do not imply restrictions on further content proliferation (P2P networks, for example), but stipulate compensation for content consumption only. TIRAMISU is consequently a super-distribution framework. Such philosophy is based on the conviction that doing so within the context of interoperable DRM systems, content will reach a larger number of potential customers to the benefit of providers and consumers. In this respect the TIRAMISU approach clearly contrasts the philosophy of established content protection policies that rely on copy-protection and forward-lock mechanisms to prevent C2C distribution.

A major requirement to be addressed when dealing with multi-channel delivery is interoperability both in terms of content representation and DRM. Within TIRAMISU this is addressed by relying on open standards (MPEG-4, MPEG-21 and ISMA – International Streaming Media Alliance). Content is abstracted as a Digital Item (DI) and in this form traverses diverse delivery channels and is consumable on a variety of devices. Since convergence to a single set of standards is unlikely, TIRAMISU also explores how bridging between delivery channels and DRM systems can be achieved.

Home domain, networked devices
Central to the TIRAMISU framework is the concept of home domains, in which content may circulate between different devices, e.g. from the living room hi-fi system to the car stereo, to the MP3 player. Content usage policy enforcement at the end-user side is left to hardware in form of smartcards. Smartcards also provide the link between the user and the home domain concept. The TIRAMISU user may own several smartcards that are registered to a particular home domain and can be used on any compliant device.

Conceptually the set of devices belonging to a user or a group, for example a family, forms a personal space where content may circulate. This concept implies that content rights purchased for a piece of content are persistent over all devices of the home domain. Eventually, from the content consumption perspective there is no difference whether the user owns one or several devices (Figure 2).

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Figure 2: The concept of home domain.

Technically the concept of home domain opens several issues due to the fact that rights pertaining to a DI are not bound to a single device or to a single smartcard. Consequently a mechanism for guaranteeing that the same set of rights is persistent on all devices of the home domain is necessary. Additionally, content must be adapted to fit the diverse rendering capabilities of each consumption device.

While smartcards can guarantee that a descrambling key is provided only when a right exists, the device that is using this key is also an important part of the system. Some rules are necessary in order to make this device compliant with TIRAMISU. Depending on its capabilities, these rules can be more or less restrictive. The extreme case is for a device allowing to trans-code content, as in this case it manipulates clear content. The framework could be extended to include some revocation rules for devices.

TIRAMISU architecture extends beyond other initiatives and their definition of the home domain concept by providing wider support for redistribution of content through super-distribution independent of the distribution channel, where the actual C2C distribution is conceptually distribution of content from one home domain to another.

TIRAMISU framework architecture
Figure 3 provides a block diagram of the TIRAMISU framework architecture with the basic content flows through the system. The TIRAMISU architecture is based on the principles that content in the framework is represented as an MPEG-21 DI. The architecture in Figure 3 identifies the five main entities in the system each with a specific role: the content author, the content owner, the content distributor, the license distributor and the end-user or content consumer. The content author is the entity that authors the media resources and transfers its IPR over to the content owner. The content owner is responsible for specifying the consumption terms and conditions and selects target distribution mechanisms over which the DI will be distributed. With a particular license termed sharing license, the content owner delegates the process of license distribution to a selected license distributor, which is responsible for issuing domain licenses to end-users. Eventually, the content distributor delivers DI comprising the resource suitable for a target usage environment to the end-user.

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Figure 3: TIRAMISU architecture.

TIRAMISU features and properties
Smartcards and home domain management
A home domain is a group of devices that feature the same set of rights in terms of content consumption. In TIRAMISU the process of license enforcement is delegated to smartcards. All smartcards belonging to a particular home domain share a cryptographic secret that is essential to enforce consumption licenses. Before a smartcard becomes usable in the context of a home domain it must be registered with the home domain manager. All smartcards registered to the same domain and consequently sharing the same cryptographic secret are able to enforce licenses issued to their domain. In other words if a license was bought using one smartcard, the associated DI can be consumed on all other devices with a smartcard belonging to the same home domain.

Super-distribution between home domains
Once the end-user has obtained the domain license, he has the right to consume the associated DI on all devices belonging to his home domain as the smartcards of the home domain can access the descrambling key from the domain license. Additionally, the DI can freely be super-distributed to other home domains, as the descrambling key embedded in the domain license that is issued for a particular home domain can not be read by a smartcard which does not belong to that domain.

The importance of smartcards
Smartcards represent a secure element in an insecure environment. Smartcards in home domains provide a secure repository for home domain secrets and are the elements that enforce the domain license by validating it before providing the content descrambling key to the rendering device. Compared to software-based solutions, the smartcard being a hardware device is more difficult to compromise and it thus offers an increased level of security.

User anonymity
The TIRAMISU KMS may under certain circumstances guarantee complete end-user anonymity and privacy. Domain licenses are issued to home domains not end-users. The end-user only needs to expose his identity to enable billing related to license acquisition. However, in cases when smartcards also serve as a mechanism for payment (pre-paid smartcards), the end-user anonymity and privacy can be guaranteed.

Is TIRAMISU the next hot technology?
DRM frameworks, such as Windows Media and iTunes, already exist, with a certain degree of success. They have not swept the media world because they are based on proprietary technology that targets closed systems. The success of the TIRAMISU concept depends on its acceptance as a worldwide open international standard. There are several key factors that might accelerate or block such acceptance, namely:

Acceptance by content providers. This is probably the biggest hurdle. The movie industry does not have a good record of adapting to new technology. Back in the 1980s, the movie industry faced a new technology that supposedly threatened its bottom line – the VCR. The threat looked so alarming, that Jack Valenti, the long time head of the Motion Picture Association of America (MPAA), compared the VCR to no less than the Boston Strangler, and the MPAA took the battle against Betamax to the US Supreme Court.

Fortunately for everybody involved, the MPAA lost the battle. The Supreme Court accepted the right of fair-use coping, and ruled against the movie industry. We all know what happened to the VCR: not long after that defeat, the studios discovered that tape rentals were even more of a cash cow than movie tickets. We are probably in the same situation now. The movie industry is already resorting to legal actions against the new technology. Hopefully legal systems will learn the lesson quicker than the industry and will refuse to cooperate with its strategy, leaving it no choice but to embrace technology instead of fighting it.

Acceptance by consumers. Assuming the pervasiveness and ease of illegal file sharing, it initially seems difficult to expect that the consumers, being used to cost-free media consumption, will be motivated to revert to a paying system. However a deeper analysis of the situation reveals that cost is not a major factor. If the cost is right, and the protection measures are unobtrusive, an atmosphere of legal business will be created and most consumers will be happy to be part of it. Just like people are happy to tip for a service or voluntarily deposit the cost of the evening newspaper in the open box.

Acceptance by media distribution industry. The move from B2C to C2C means less business for the Businesses, which are expected to battle such a move. Eventually they will need to accept market reality and adapt their business accordingly. The businesses which display the flexibility to adopt new technologies for inventing new business models based on service aggregation will prevail, just like the emergence of tape rental shops didn’t obliterate the movie theatres.

Emergence of a single standard. This is a key factor in accelerating the acceptance of the three market segments referred to above. TIRAMISU tries to show the way by picking from existing standards, but the same concept can be realised with a different set or variations of standards. This will not be regarded as a failure since the importance of the framework is in its concept rather than the implementation details.

Worldwide embrace of smartcard technology. This actually has already happened. Smartcards are already embedded in cellular phones, which are rapidly evolving into integrated media players. Many PCs already shipped equipped with smartcard readers. The ease and cost of incorporating smartcards in every media consumer device is minimal.

Tamperproof technology. One may claim that in order for a DRM system to succeed it has to prove to be tamperproof, and since such a proof has to persist over time, the adoption of the technology must be delayed. However the state of the market demonstrates that immunity of systems to bypassing is not a major issue. Consumption is not a zero-sum game. As with the VCR, legal and profitable business continues to thrive despite fraudulence. In many cases the fraudulence helps the promotion of the profitable business. There is little doubt that unobtrusive DRM can sweep the market.

Bottom line
The end-to-end framework for content creation, delivery and protection as conceived within the IST-TIRAMISU project is independent of the distribution channel. It is based on open standards such as MPEG-21 and ISMA and provides full support for super-distribution. The increased security of the framework is a consequence of the application of smartcards for the manipulation of sensitive data. From the consumer's point of view, the TIRAMISU framework provides several features rendering the DRM system unobtrusive.

Sources
  • Lauchlan, S. (2001): Content is king. Internet World, November 2001
  • Burnett, I, van de Walle, R.; Hill, K.; Bormans, J.; Pereira, F. (2003): MPEG-21: Goals and achievements. IEEE Multimedia, vol. 10, no. 4, pp. 60-70, October/December 2003
  • Bormans, J. and Hill, K.: MPEG-21 overview v.5. ISO/IEC JTC1/SC29/WG11, Shanghai, October 2002
  • Bormans, J.; Gelissen, J.; Perkins, A.: MPEG-21: The 21st century multimedia framework. IEEE Signal Processing Magazine, pp. 53-62, March 2003
  • TIRAMISU web site http:// www.tiramisu-project.org.
  • Marušič, Boštjan; Dobravec, Štefan; de Cuetos, Philippe; Concolato Cyril; Piron, Laurent, Tasič, Jurij F.: TIRAMISU: A novel approach to content representation and key management for seamless super-distribution of protected media; to be published in “Signal Processing: Image Communication, Special Issue on European projects on visual representation systems and services”, Fall 2005.

About the authors
Dr. Boštjan Marušič is a full-time researcher at the Laboratory for digital signal processing of the University of Ljubljana. His research interests include wavelet image and video coding, telecommunication systems and networks, Internet. Contact: bostjan.marusic@fe.uni-lj.si

Philippe de Cuetos is a research scientist who is designing and implementing innovative services for multimedia content management. He holds a PhD from ENST and has recently joined Expway. Contact: philippe.de-cuetos@expway.com

Laurent Piron works at Nagravision. His main focus is on mobile television. He has 10 years experience in video compression and conditional access on TV systems. Contact: Laurent.Piron@nagra.com

Zvi Lifshitz is a senior software architect in Optibase. He is a major contributor and the representor of Israel at the ISO's MPEG committee, where he has led the IM1 Software Platform group and now participant in MPEG-21 and MPEG-A workgroups. Contact: zvil@zvil.com

Status: first posted 27/07/05; included in INDICARE Monitor Vol. 2, No. 5, 29 July 2005; licensed under Creative Commons
URL: http://www.indicare.org/tiki-read_article.php?articleId=125