Research on DRM interoperability

This section reviews how previous researchers have addressed DRM interoperability.

Koenen et al. (2004) proposed three different approaches to achieve DRM interoperability: full format interoperability, connected interoperability, and configuration-driven interoperability.

Full format interoperability expects agreements between all participants to use the same data representation, encoding, protection scheme, trust management, key management, etc. In other words, a full industrial standard of DRM and the common practice of its compliance are expected, e.g. CD and DVD (Koenen et al. 2004).

Connected interoperability expects online service providers to solve the interoperability problems caused by different DRM systems. As a service-centric solution, DRM systems need to negotiate with the online service and then the online service instructs the terminal devices how to perform accordingly. Thus, the connection between the online service and the terminal device is required. UltraViolet from Digital Entertainment Consortium Ecosystem (DECE) is a good example of the approach (Kalker et al. 2012).

Configuration-driven interoperability expects tools or components for specific DRM systems to be installed/configured on the terminal device or software application. As a device centric solution, DRM systems need to provide compatible components or tools to the consumer devices. A good example of the approach is MPEG-21 IPMP (Rump 2004).

Figure 16. The architectural view of different approaches for DRM interoperability

As illustrated in Figure 16, the three approaches represent three distinct architecture options. The full format interoperability leverages with a universal standard to replace distinct DRM systems. Both the connected interoperability and the configuration-driven interoperability embrace the differences among DRM systems and provide interoperability framework to bridge the differences among DRM systems. The connected interoperability integrates DRM systems as plugins on the service side while configuration driven interoperability integrates DRM systems on the device side. The interoperability frameworks from both the connected approach and the configuration-driven approach could optionally expose system-agnostic interfaces to the compatible applications on devices. It is worth noticing that the configuration-driven interoperability can be utilized in the DRM agent switch mode as DRM system plugins for the interoperability framework can be as sophisticated as a fully functional DRM agent on the device. In such a case, based on the content, a DRM agent from a corresponding DRM system can be selected by the interoperability framework to handle the content and its associated rights. The interoperability framework in this case merely provides common interfaces for both applications and DRM agents to integrate with and perform matchmaking when the application is fed with a DRM protected content. However, the DRM agent switch mode is an extreme case for configuration-driven interoperability. As it does not bridge among DRM systems, it does not help with system interoperability.

Moreover, as each DRM system has implemented their fully functional DRM agent on the target device, the device interoperability should have been covered. The interoperability framework in this case merely eases the effort to achieve application interoperability. On the other hand, the configuration-driven interoperability can

accommodate system interoperability as well. This dissertation leaves the DRM agent switch mode out of scope when referring to the configuration-driven interoperability.

Standardization is important for DRM interoperability. Koenen et al. (2004) recommended applying the full format interoperability whenever possible. Despite the efficiency that the full format interoperability would bring to the whole industry, developing the required industry standard can be a long process. Still, a few attempts in DRM standardization have gained a certain level of industrial attention, such as OMA DRM and Marlin (Keoh 2011). If the full format interoperability is the long term recommendation, then any steps towards it are seen as a positive progress.

Meanwhile, Torres et al. (2008) argued that closed DRM systems are not suitable for the interoperability problems and only open DRM provides needed conditions to achieve full interoperability. Thus, even for the connected interoperability or the configuration-driven interoperability, it is encouraged to standardize the solution.

MPEG-21 IPMP (Rump 2004) is a good example of standardization for the configuration-driven interoperability.

The configuration-driven interoperability hosts an interoperability framework totally on the target device. This feature not only enables the offline mode for DRM interoperability but also exposes a potential security risk as it is difficult to push a fix for a breach in the interoperability framework to an offline device. The connected interoperability, on the other hand, places the interoperability framework on both device and service side. Even on the device side, due to its connected nature, upgrades to the framework can be easily achieved. Moreover, as each DRM system includes both client and server components, the connected interoperability is one step closer towards the full format interoperability compared with the configuration-driven interoperability.

Schmidt et al. (2004) proposed an intermediated DRM solution which adopts the approach of connected interoperability. They concluded four generic tasks the intermediaries need to perform:

Content and rights reformatting transforms the content format into a one the target device can consume and transforms the rights expression into a one the DRM system on the target device can govern.

Safavi-Naini et al. (2004) noticed that Schmidt et al. (2004) did not discuss how tasks above shall be implemented. They extended the discussion on the concept of import and export in DRM. Safavi-Naini et al. (2004) claimed that their approach is close to the connected interoperability. However, they did not rely on on-line third-party for condition evaluations. They indicated that the import and export tasks could be shared between the connected interoperability and the configuration-driven interoperability. Safavi-Naini et al. (2004) put an effort on handling the rights translation when discussing the import and export in DRM. Rights exporting seems to require more research compared with content exporting.

This dissertation focuses on the task of rights exporting initialized by Safavi-Naini et al. (2004). The task is a concrete implementation of the generic tasks Schmidt et al. (2004) proposed for the intermediated DRM solution. Rights exporting can be applied to both the connected interoperability and the configuration-driven interoperability categorized by Koenen et al. (2004).