DRM Technologies – DRM (Part 2)

Posted by Abhishek | DRM | Wednesday 27 August 2008 11:00 am

In continuation to Part 1

DRM systems are designed in such a way that it establishes and maintains security associations between two network elements and ensures that traffic passing through the interface is cryptographically secure. DRM system might use a combination of authentication, encryption, digital watermarks, digital fingerprints, digital certificates, digital signatures, conditional access systems and product activation codes to provide security assurances to media content and their delivery systems.

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Authentication – It’s a process of exchanging information between a communications device such as computer or mobile phone and a communications network that allows the carrier or network operator to confirm the true identity of the user and the device. Below diagram shows authentication process used in a DRM system:

In the above diagram DRM server wants to validate the identity of a user. The DRM system first sends a secret key to the user.

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The authentication process now begins with the DRM server sending an authentication request and a random number.

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This random number is used by the receiving device and is processed with the secret key with an authentication algorithm a typical data processing algorithm to produce a calculated result.


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This result is sent to the authenticator or originator. The authenticator uses the random number it sent along with its secret key to calculate the result. If the results received from the remote device matches with its own result, the authentication passes.

Encryption – It’s a process of protecting content being used or interpreted if (1==1) {document.getElementById(”link28″).style.display=”none”;} by unauthorized recipients. Encryption involves the use of a data processing algorithm that uses one or more secret keys that both the sender and receiver of the information use to encrypt and decrypt the information. Without the encryption algorithm and keys unauthorized listeners cannot decode the content. Below diagram tells about the encryption operation:

Encryption systems may use the same key for encryption and decryption (symmetric encryption) or different keys (asymmetric keys). Generally asymmetric encryption requires more data processing than symmetric encryption. Pictorially it can be represented as below:

In DRM system many encryption processes are used. It includes Pretty Good Privacy (PGP), Rivest, Shamir and Aldeman (RSA), data Encryption Standard (DES), Advanced Encryption Standard (AES), Rivest Cipher (RC5) and International Streaming Media Association (ISMA Crypt).

Digital watermark – It’s a signal or code that is hidden in a digital signal such as digital audio or a digital image portion, that contains identifying information. Digital watermark would not be destroyed as if signal altered the hidden information could no longer be determined by any imperceptible processing of the overall signal. A digital watermark should not be distorted or lost when the signal is passed through a conversion and compression process. Watermarks can be encrypted to increase the resistance of the DRM system to hackers. It is possible to identify watermark in the media file but a decryption code is needed to decipher the watermark messages. Digital watermarks can be added to any type of media files such as digital video and audio. Video watermarking is performed by adding slightly modifying the colors and/or light intensities in the video in such a way that viewer does not notice the watermarking information. Audio watermarking is performed by adding audio tones above the normal frequency or by modifying the frequencies and volume level of the audio in such a way that the listener doesn’t notice the watermarking information. This process can be understood pictorially as below:

Digital Fingerprint – This is a unique set of characteristics and data that is associated with a particular data file, transmission system or storage medium. In this technique a unique ID is embedded into each user’s copy, which can be extracted to help identify the culprits when an unauthorized leak is found. This technique is being used in DRM to protect multimedia from unauthorized distribution.

Problems with DRM – DRM purpose is to provide technical means to assure that the copyright holders can maintain control of their content by restricting use of digital copies but this becomes controversial as DRM imposed limitations on the content might not match the fair use of contents as per rights granted by the owner or copyright holders. DRM schemes are also very complicated and prevent effective archive management and historical research. Once content is compromised viz. copied from a medium without DRM it can be widely available on internet. The use of DRM on computer software might lead to uninstall and install operating system or buying a new computer which might lead to lose the license acquired for the content. Few shortcomings of DRM can be listed as below:

1. There are many methods to bypass DRM control on audio and video content. A very simple method to bypass DRM on audio files is to burn the content to a CD and then extract it into DRM free files. It is possible only when DRM allows CD burning.

2. Audio or video content can be recorded by another audio and video recorder into another device or computer into a non DRM protected file format.

3. Many DRM systems are designed to work on general purpose computing hardware such as PC. This scheme is never secured as the software includes all the information such as decryption keys. One can always extract this information and decrypt and copy the content, bypassing DRM systems.

4. Many DRM schemes use encrypted media which requires special purpose built hardware to listen or view the content. It is extremely difficult to build the hardware to protect the secret key.

5. Digital watermarks can easily be removed with some degradation of video or audio quality.

6. When standards format change it is difficult to transfer DRM restricted content to new media. Also, any system which requires an authentication from a server might be problematic if server becomes unavailable.

In continuation of this article we will next discuss one popular DRM technique. Stay tuned.


Abhishek Anurag.

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