Content +Access Framework Overview

The Content Access Framework (CAF) provides a common interface for applications +to access Digital Rights Management (DRM) protected content. An application +might be a video or sound player or an internet browser and DRM content might +be a media files or a game.

Purpose

CAF provides a single point of access to +all functionality related to DRM-protected content.

Access to DRM-protected +content for content consumers, such as media players or software installers
Management of DRM protected +content
Import DRM protected +information
Notification on DRM +related events, such as rights expiry
Implementation of new +DRM schemes

Key concepts +and terms

Content: Content is logically-coupled data such as a movie, a soundtrack or +a ringtone forming a content file.

Content consumer: Content consumers are applications such as media players or software +installers that access DRM-protected content.

Content access agent: A content access agent is an ECom plug-in which implements the CAF +interface and performs the following functions:

+
Provides access to protected +content such as MPEG and MP3, and allows viewing them as plain text (even +if the content is encrypted).

+
Provides indirect access +to a private server directory.

+
Provides platform security +enforcement. CAF does not provide any capability enforcement so the agent +must police access to the APIs. The agent can choose to deny some operations +in the CAF API based upon both the application's capabilities and the agent's +policy.

+

F32 agent: The F32 agent provides access to unprotected files. CAF treats the +F32 agent as a special case. If no other agent is responsible for a file or +directory, the F32 Agent is used.

The F32 agent runs in the same process +and thread as the calling application, so its file operations are limited +to the capability of the calling application's.

Handling and sharing content in a private directory: Few agents can provide access to files stored in their private directory. +They can share their files existence to applications through implementation +of the ContentAccess::CAgentManager::GetDir() function. +In the file system the private directories have the format:

\private\xxxxxxxx\directory_1\...directory_n\filename.ext

where xxxxxxxx is the UID of the agent.

CAF +will translate that path so applications see the file as:

\private\agent_name\directory_1\...directory_n\filename.ext

where agent_name is the name of the agent.

When +an application opens a file stored in the private directory, CAF selects the +agent which handles that content based upon the name in the path. If the file +is not stored in a private directory, CAF asks each of the agents in turn +whether they support the file. If no agent supports the file, it will be read +as plaintext using the F32Agent.

Architecture

CAF provides interfaces for applications +to read both unprotected and DRM protected content. It behaves as a switch +between different Content Access Agents.

CAF uses a client-server +architecture. The CAF client DLL must be linked with the client process. CAF +agents can be implemented as plug-ins to the CAF client if they do not require +access to keys or rights. An agent requiring access to encryption or decryption +of keys, or rights must be implemented as a server-side plug-in. A server +side plug-in must ensure that only applications with the right capabilities +can access the content.

Each agent is an ECOM plug-in implementing +the content access agent interface UID 0x10204740. The agents can run in separate +processes and need not have the capability to open files in the TCB or private +server directories using just a file name. Files must be opened by the process +that owns them and an open RFile handle passed to CAF to +read it.

In the following diagram the yellow blocks represent the +components provided by Symbian and the blue blocks represent the components +that must be implemented by device creators.

+ CAF Architecture + +

Note: The F32 agent is a client-side implementation as it +is used for accessing unprotected content only.

Key classes

The following table summarizes the +important classes provided by CAF:

Note: The classes below +are defined within the namespace ContentAccess

+ + + +Class +Description + + + + +

CSupplier

Delivers and transforms content into a secure format for storing +it in the device

+ + +

CContent

Provides read access to content (including protected content) stored +in a device.

+ + +

CManager

Manages files and content access agents

+ + +

CRightsManager

Manages DRM rights for a specific CAF agent

+ + +

CData

Allows clients to read data from a content object

+ + +

CAgentFactory

Represents the ECom interface for a CAF Agent. A CAF agent must +implement a concrete factory derived from ContentAccess::CAgentFactory.

+ + + +

The above APIs are grouped as follows:

Supplier API

The +classes ContentAccess::CSupplier and ContentAccess::CImportFile together +represents the supplier API.

The Supplier API handles the delivery +and transformation of content. It is used to transform DRM protected files +when they arrive on a device into a compatible format for storing it securely +on the device. It is also used to intercept content and ensure it is stored +in an agent's private directory.

Consumer API

The +classes ContentAccess::CContent and ContentAccess::CData together +represents the consumer API.

The consumer API allows applications +to view the content as plain text, regardless of how it is actually stored +on the device. (For instance, it might be encrypted). It is used by applications +to render content and multimedia plug-ins. Note: Rendering implies +reading data from a file, transforming it, then playing or displaying it on +the device.

Manager API

The ContentAccess::CManager class, +which manages the files and content access agents forms the manager API.

Rights +Manager API

The ContentAccess::CRightsManager class, +which manages DRM rights within a particular DRM agent forms the rights manager +API.

Agent API

The ContentAccess::CAgentFactory class +forms the agent interface. It allows to integrate new agents at a later date, +dynamically if required. The agent's factory produces products derived from +the following:

ContentAccess::CAgentContent
ContentAccess::CAgentData
ContentAccess::CAgentImportFile
ContentAccess::CAgentManager
ContentAccess::CAgentRightsManager

Typical uses

CAF provides interfaces for implementing +and using CAF agents. CAF agents allows authorised users to access the DRM +protected content for installation and playback. CAF APIs can be used to perform +the following tasks:

Handling delivery and +transformation of DRM protected content. For more information, see Supplier +API Tutorial.
Providing services for +applications that render content and multimedia plug-ins. For more information, +see Consumer API Tutorial.
Managing files and CAF +agents. For more information, see Manager +API Tutorials.
Managing DRM rights +within a particular DRM agent. For more information, see Rights +Manager API Tutorial.