Digital Personal Property

Paul Sweazey believes he has found the solution that mitigates the problem of DRM. He wanted to emulate a property of physical goods: rivalry (If you want more information about rivalry, please have a look on Bomsel’s works). In a nutshell, rivalry is the fact that when consuming a good you reduce the access for others. For instance, when you play your DVD, someone else cannot play it on another player. This is not true for electronic files. By definition, electronic goods are non-rival. One of the purposes of DRM is to add a pinch of rivalry.

To do so, Sweazey created the concept of Digital Personal property. How does it work? Content has two elements: an encrypted folder containing the essence and a playkey that you preciously keep in a vault. Sounds familiar, isn’t it? In DRM vocabulary, his playkey is called a license. You may freely distribute the encrypted folder but will give your playkey only to trusted people who would not steal your license. The license must be UNIQUE in the sense that there is one unique instance at any time. Thus, if the person you gave your playkey does not return it, you lost its ownsership.

The technical trick will be to be able to create a rival license that should not be linked to a device (else you end up with the typical problem of interoperability).

He just moved the problem of DRM towards the license. He will still have to find a method to generate a license (playkey) that can exist only as one unique instance in the world and that could be played everywhere. This is the Holy Grail of DRM that we have been all looking for years. TCreating rivalry is difficult without introducing physical constraints.

It reminds me one of the concepts we built in an old system called SmartRight. The objective was to control the size of an authorized domain for a familly but without any central online authority. We used an electronic token that was passed to the newly joining device. Of course, you could add a device from your neighbour, but then your neighbour “owned” the electronic token. Would the neighbour leave or not collaborate anymore, you could not anymore add devices to your domain. It was based on the use of secure processors and on the fear of loosing the token.

Will DPP work? If Sweazy finds a robust and user friendly way to create this unicity of instance, it would work. This would also offer a lot more applications. But is it feasible? Bruce Schneier would probably say no. (Wait our next security newsletter with his interview.) And many brains are researching this topic.

For more information, read Goodbye, DRM; hello “stealable” Digital Personal Property at Ars technica.

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