DRM Technologies – DRM (Part 1)

Posted by Abhishek | DRM | Tuesday 12 August 2008 5:47 pm

In continuation of our series of articles about Digital Rights Management Technologies.

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This is the second technology we shall cover. The first technology article can be found here CPRM.

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Digital Rights Management (DRM)

DRM – Is one of the access control technologies created for copyright holders and publishers to limit usages of digital media.

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It came into picture as copyright holders wanted to prevent unauthorized duplication for their work to generate revenue continuously.


All major content provider companies are using some form of this technology e.g. Sony, Apple, Microsoft, BBC, etc. to name a few.

DRM operates on three levels: for the piece of content establish a copyright, for this content manage the distribution and then finally control what the consumer can do with this distributed-copyrighted-content. To establish this level of control following entities are involved: user, content, usage rights and the relationship between them.

List of actions covered by DRM is huge but at high level they can be categorized into following:

  1. When is the content available for consumption
  2. On how many devices can the content be consumed and if it can be passed between devices or not
  3. How many times the content is consumed or expiration date
  4. How long will the content be available for consumption
  5. Can the user backup and restore the license of the content

DRM systems work basically on content being secured by public key encryption processing where the encryption key has two parts (Public Key, Private Key) that are bound by a special mathematical property. This property allows encryption of the data with one part of the key and decryption with the other part. A high level representation of typical DRM system is shown below:

Anurag wants to buy a piece of media content (music track or video clip) from an online store. As first step Anurag sends his Public Key to the Content server. The content server in turn sends this public key and appropriate media to the DRM gateway. Abhishek pays the appropriate amount of money to the DRM gateway depending on the type of usage rights he wishes to acquire. The DRM gateway then creates an encrypted package of media file and the usages rights. This package is encrypted using the Public Key sent by Anurag. This package is then sent to Anurag who can decrypt the package using his private key. The usages rights acquired by Anurag dictate how the content gets played. Now suppose Anurag forwards the content to his friend Amit. Amit cannot decipher the package unless the package is encrypted with Amit’s public key upon which he can decipher the package and consume the content. For this Amit will have to use the same procedure as followed by Anurag and pay to the DRM gateway to get the desired encrypted package. As can be seen in this example the media rights are limited to the legitimate users.

Coming back to the whole DRM process, the commonly deployed scheme has following components:

  1. Content Packaging – Digital media files are encrypted and locked with a key and packaged by DRM. The key is kept with encrypted license and distributed separately. All needed informations are also added in media file viz. how to acquire the license, from which location to acquire this, etc. The packaged media file is saved into a suitable format which can be played by the user on supported devices.
  2. Content Distribution – Packaged contents are placed on content server on the web for download. Packaged contents can be downloaded, streamed, distributed on a CD, etc. DRM also ensures super distribution too.
  3. Establishing a License Server – Content provider works with DRM Gateway or license server to store license having all the rules and specific rights with that content. DRM Gateway implements all license services and authenticate user’s request for a license. Digital media files and license are stored and distributed separately so that entire DRM system can be managed easily.
  4. Acquiring License – Once user gets packaged media file he must have to acquire the license key to unlock the content and play. License acquiring process can start either when user gets the protected content or plays the media file for the first time. He might have the predelivered license too. DRM ensures that license is getting acquired and content provider is getting paid.
  5. Playing Media file – Media file will only be played on a media player as per the rules and regulation of the license acquired for the content and the player must support DRM. License usually have different right viz. start times, dates, duration, number of times the content will be played, to play the file on a specific device and copy that to another portable device, how many times content can be copied to another device, etc. Licenses can’t be transferred that’s why if a packaged file is forwarded to a friend, he must have to acquire his or her own license to play that content. By this way DRM ensures that packaged media file can only be played by the device for which license key was granted.

A typical DRM processes and schematic can be represented as below:

Let’s break here for now and we shall continue this discussion in the next part of this article.

To be concluded…


Abhishek Anurag.

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