Introduction to DRM, DRM Systems – from IP Television Magazine.

DRM Series

DRM Systems
by: Lawrence Harte

DRM systems are a combination of processes, programs and hardware that facilitate the assignment, management and enforcement of the rights associated with digital media. DRM systems can usually identify and describe media, assign and find rights associated with that media, ensure that requests for media come from authorized users and manage the distribution and enforcement of rights.

Media communication systems are usually composed of unknown (untrusted) and known (trusted) devices. Untrusted devices are hardware components or software applications that are unknown or not validated with a provider of data or information. An untrusted device may require authentication based on some type of user interaction before access is granted. A trusted device is a product or service that is previously known or suspected to only communicate information that will not alter or damage equipment of stored data. Trusted devices usually allow privilege levels that could allow data manipulation and or deletion.

DRM systems are typically setup as client server systems where the system receives requests and provides services to clients. A DRM

This article is Part 6 of a 9 Part Series
DRM Series List	Month

Digital Rights	Aug 06
Rights Management	Sep 06
Digital Assets	Oct 06
Media Identification	Nov 06
Security Processes	Dec 06
*DRM Systems*	*Jan 07*
Media Distribution	Feb 07
Rights Threats	Mar 07
Protocols and Standards	Apr 07

system server may include the content server (the content source), content descriptions (metadata), DRM packager (media formatter), license server (rights management) and a DRM controller (DRM message coordinator). A DRM client typically includes a DRM controller, security interface (key manager) and a media decoder.

Figure 1.20 shows a sample network architecture that could be used for a DRM system. This diagram shows a client that is requesting

Figure 1.20., DRM Architecture

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content and that a server processes these requests. When the user requests access to content, the DRM server first validates the identity (authenticates) of the user by using shared secret information that the client should possess. The DRM system then reviews the authorization of the user for this content and assigns rights for this use of content. A key server assigns and transfers keys that are used to encode and decode media and control messages. The license server may initiate an encryption code that is used to process the media. The DRM packager uses the encryption code to process the content and its associated descriptive (metadata) content. When the encrypted file is received in the client, the security interface may be used to gather the necessary keys and parameters necessary to decode the encrypted information.

Content Server

A content server is a computer system that provides content or media to devices that are connected to a communication system (such as through a television system). The content servers' many function is to receive and process requests for media content, setup a connection to the requesting device and to manage media transfer during the communication session. Content servers are typically protected from direct connection to access devices by firewalls or media packing devices.

Metadata

Metadata is information (data) that describes the attributes of other data. Metadata or meta-tags are commonly associated in media files or programs to describe the attributes of the media content. These attributes typically include the title of the media, media format details (media length and encoding formats) and may include additional descriptive information such as media category, actors or related programs.

DRM Packager

A DRM packager is a program or system that is used to combine content (digital audio and/or video), product information (e.g. Metadata) and security codes to a media format or file that is sent from a content provider to a user or viewer of the content.

License Server

A license server is a computer system that maintains a list of license holders and their associated permissions to access licensed content. The main function of a license server is to confirm or provide the necessary codes or information elements to users or systems with the ability to provide access to licensed content. The license server may download a key or other information to client devices that enables a license holder to access the information they have requested.

License servers use licensing rules to determine of users or devices have authorization to access data or media. Licensing rules are the processes and/or restrictions that are to be followed as part of a licensing agreement. Licensing rules may be entered into a digital rights management (DRM) system to allow for the automatic provisioning (enabling) of services and transfers of content.

Key Server

A key server is a computer that can create, manage and assign key values for an encryption system. A key is a word, algorithm or program that used to encrypt and decrypt a message that is created in a way that does not allow a person or system to discover the process used to create the keys.

DRM systems may have the capability to transfer and update keys (key renewability). Key renewability is the ability of an encryption system to issue new keys that can be used in the encoding or decoding of information.

DRM Controller

A DRM controller is the coordinator of software and/or hardware that allows users to access content through a digital rights management system. DRM controllers receive requests to access digital content, obtain the necessary information elements (e.g. user ID and key codes), performs authentication (if requested) and retrieves the necessary encryption keys that allows for the decoding of digital media (if the media is encoded).

DRM Client

A digital rights management client is an assembly, hardware device or software program that is configured to request DRM services from a network. An example of a DRM client is a software program (module) that is installed (loaded) into a converter box (e.g. set top box) that can

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request and validate information between the system and the device in which the software is installed.

DRM clients may communicate with a module (such as a smart card) or external device to manage keys and decryption programs.

Media Transfer

Media transfer is the process of moving media from the content owner or content distributor to the end user or through other distribution systems. Media transfer may be in the form of file downloading, media streaming or through the use of stored media.

File Downloading

File downloading is the transfer of a program or of data from a computer storage device (such as a web Internet server) server to another data storage or processing device (such as a personal computer). File download commonly refers to retrieving files from a remote server to another device or computer. File downloading is primarily used for non-real time applications such as when a program or application is completely downloaded before it is played or used.

Figure 1.21 shows how file downloading can be used to download movies through the Internet before they are viewed. This diagram shows how the media server transfers the entire media file to the media player before viewing begins. Because the media file has been completely downloaded before playing, this allows uninterrupted viewing and navigation (e.g. play, stop, rewind or fast forward).

Media Streaming

Media streaming is a real-time system for delivering digital media through a data network (such as an IP data network). Upon requesting a program, a server system will deliver a stream of media (such as audio and or video) to the requesting client device (such as a personal computer). The client will receive the data stream and (after a short buffering delay) decode the audio and play it to a user.

Media streaming uses protocols to control the flow of information and the devices that provide (stream) the media. Examples of media streaming protocols include real time protocol (timing information), real time control protocol (QoS information) and real time streaming protocol (media server flow control)

Streaming media can add DRM by dividing encrypting the entire stream or by dividing the media segments and periodically changing the encryption keys.

Figure 1.22 shows how MPEG enables the use of conditional access and digital rights management systems. This example shows that the MPEG system may use a combination of user keys and service keys to scramble the MPEG signal. This example shows that the conditional access table (CAT) provides the PID for the EMM and the program map table (PMT) provides the PID for the EMC. The receiver uses these messages along with other information (such as the smart card) to descramble the MPEG signal.

Figure 1..21., Movie Downloading Operation