What are the requirements for this - The Filter module

The paramount requirement for the above mentioned procedure is that the application (i.e. the multimedia or hypertext system) is capable of handing down information on media structure, structural elements or document types to the security platform. An application document therefore must be split into its multimedia or structural components which in turn must be passed on in Plasma-specific formats to the security platform. This task is performed by the Filter .

The Filter is a module that is required by the security platform yet logically resides within the application since only the application has the knowledge required on format structures which vary from application to application and may even diverge strongly from prior versions of the same application. Therefore each application must provide its own Plasma Filter . The data structures within Plasma for multimedia documents are constant and can be addressed by each application in a similar fashion; it is the application formats which cannot be addressed adequately in a general form by Plasma.

A Filter dissects a multimedia document of the application into its media specific components by noting the locations of subcomponents (e.g. the locations of textual and image parts) into a Script ; the media specific parts of an application document are thus transformed into their corresponding media specific data objects within Plasma.

If after reverting the cryptographic operations these media specific data objects of Plasma are to be transformed back into the plaintext document, the Filter requires this Script . The Script provides the required information for the Filter to assemble the plaintext document into its original form; the Plasma specific text objects are written into positions originally containing text portions; similar procedures are followed for image data and other media specific objects within Plasma. Figure illustrates the concept of a Filter .

  

Figure: The functionality of a Filter

Plasma thus obtains media specific data objects from the Filter which are then to be processed using various cryptographic mechanisms.