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Self-manifestation of composite multimedia objects to satisfy security constraints

A composite multimedia object (cmo) is comprised of different media components such as text, video, audio and image, with a variety of constraints that must be adhered to. These constraints include synchronization and spatial relationships between components, as well as the confidentiality and integrity requirements on each component. While spatial and synchronization constraints are to preserve the semantics of the cmo, the security (confidentiality and integrity) constraints are to represent the access control policies and fidelity requirements. A subject (user) requesting access for a cmo may not possess the required credentials to meet the confidentiality constraints, or his computer system the desired capabilities to meet the integrity constraints. This necessitates modification to the original cmo.In this paper, we present a self-manifestation approach in which composite multimedia objects automatically manifest themselves to cater to the subjects' credentials, and the capabilities of their computer systems. We accomplish this in two steps. First, we present a logical model which is an enhanced Petri Net model, called multimedia color-time Petri net (MMCTPN) to represent the components as well as the constraints of the cmo. We then demonstrate how MMCTPN lends itself to automatic manifestation of the cmo when subject's credentials and capabilities activate it. Second, we show how the Petri net behavior can be implemented using the Synchronized Multimedia Integration Language (SMIL): SMIL, which is an extension of XML, supports specification of synchronization of the multimedia components and facilitates automatic rendering. When credentials are specified with digital certificates in some XML format, our system automatically modifies the SMIL document to satisfy the security constraints. We avoid multiple certificate verifications at the component sources by generating a single security token, when multiple credentials are required to view a component.