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.

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.

DRM Technologies – CPRM

Posted by Abhishek | DRM | Monday 12 May 2008 9:38 am

Maintaining the DRM thread here is my primer on CPRM;

In this era of computers, Digital Media (data, audio, video and other digital contents) storage and safety had never been so important be it for the users of personal computer or for other digital consumer devices such as Pen drives, USB disc, Personal Media devices.

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As for the Personal Media Devices (PMD) such as Personal Media Players (PMP) the requirement is the ability to store and move the legitimate content across systems.

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And with more popular techniques this move-ability is linked to the media and the content. From the users perspective he needs this unlimited and unrestricted access to his digital media content. However, many a times implementing a perfect scheme which will provide a seamless play-anywhere and play-unlimited capability is infeasible. Besides, while there is an expected legitimate use of this content there are various new ways devised everyday to break these content protection schemes to enable free use of protected content.

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The economics behind digital content protection/playback is huge and easily falls in the figure of multi-billion dollars every year.

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The copyright holders and publishers own the large portion of this multi-billion dollar pie and look up to the Crypto/Security enthusiast community to help them countering the problems of piracy. Various standardized and proprietary content protection (Digital Rights Management – DRM) schemes have been proposed on this topic which have been successful a large extent. One of them is “CPRM – Content Protection for Recordable Media”.

CPRM is simply a hardware based technology which controls copying, moving and deletion of digital media on computers and digital players. CPRM imposes restrictions through built in mechanisms in storage media. CPRM was developed by The 4C Entity consisting of IBM, Intel, Matsushita and Toshiba. The 4C Entity, LLC, Licensor of Content Protection for Recordable Media has defined the CPRM specifications. These specifications contain all kamagra gel cryptographic methods to protect digital media or entertainment content when recorded on physical media. The current cryptographic methods presently used are Cryptomeria cipher (C2) algorithm for symmetric encryption. CPRM specification is based on key management for interchangeable media, content encryption and how digital media is being renewed. C2 is a block cipher. The 4C Entity has defined it and has the license. C2 is successor to CSS (Content Scramble System) and mainly designed for CPRM for DRM restricted digital media and devices. The C2 symmetric key algorithm is a 10-round Feistel cipher. It has a key size of 56 bits and a block size of 64 bits.

The 4C Entity provides development or facsimile keys for the product which uses CPRM technology. CPRM is mainly implemented in Secure Digital Card and used to incorporate digital tags into storage media viz. recordable CDs (CD-R, CD-RW) and flash memory cards for MP3 players, etc. CPRM specifications have been mainly defined for DVD drives, portable ATA storage and Secure Digital (SD) memory cards. CPRM requires a table of secret device keys which should be embedded into every licensed device and media key block (MKB) which should be stored on every recordable media. CPRM complaint devices can also generate a media key by performing operations on MKB. In the case of a DVD/CD the MKB is permanently burnt into the control data area hidden within the disc’s lead-in area. Lead-in area is normally near the center of the disc and usually not accessible by users. This will prevent users from deleting or modifying MKB. Generally, disc manufacturers embed a media identifier or media ID into each piece of recordable media, which can not be deleted. Media ID specifies the type of media and it’s manufacturer and also includes a 40-bit serial number that uniquely identifies the disc. This helps to uniquely identify the disc which helps CPRM to bind the data to the media on which it is recorded. Each volume of content is also identified by a secret 64-bit title key that is stored on the disc in encrypted form. This key can only be decrypted by a 56-bit disc specific media unique key that in turn is calculated from the media key and the media ID. The title key which is needed in order to read or write content is thus bound to both content and media. Media ID doesn’t need to be kept secret as it can not be physically altered.

In nutshell, CPRM mainly binds copyrighted materials to the physical media. It allows discs to be recorded and played back on different devices but doesn’t let protected content to be copied to another piece of media. As for how successful CPRM has been could make a good debate, however, it still widely adopted by hardware manufacturers. For now I shall leave you with this much.

- Abhishek Anurag

Article series on DRM Technologies

Posted by Amit | DRM | Thursday 8 May 2008 8:57 am

DRM is like someone instructing me what I do with my own money!

The DRM debate resumed again at the Embedded System conference and it appears that the arguments this time were quite heated. Imagine Hollywood studio representatives taking on attorneys. For more on that refer to this link.

One of the interesting analogies came from Dean Garfield, executive VP and chief strategy officer for the Motion Picture Association of America. Garfield related the DRM techniques adopted by Hollywood to security barriers faced by bank customers using ATMs. These customers gladly accept the necessity of password to get their own money which is similar to the DVD buyers accepting constraints such as water marks and copy restrictions placed on the media they purchase. He referred to them as business rules and not actually the technology. So it’s the business rules that irritate and anger both consumers and IP attorneys. In response to this comment Fred von Lohmann, senior IP attorney for the Electronic Frontier Association responded “Of course they don’t mind the password at the ATM. What I would mind is a set of restrictions on what I can do with my money after I’ve received it from the bank”. He said that such constraints are the essence of DRM.

Jim Barton, CTO and senior VP of R&D for TiVo talked about closing the gap between what the consumers want and the business rules required by the content creators.

Picking up from this thread, we would like to start an article series on DRM & related technologies. We will start with a primer on CPRM and Abhishek happily has taken up the challenge to do that for us.

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