This work concentrates on proposing a framework to implement the PKI which enables security in XML documents, by defining a common framework and processing rules that can be shared across applications using common tools, avoiding the need for extensive customization of applications to add security. The Framework reuses the concepts, algorithms and core technologies of legacy security systems while introducing changes necessary to support extensible integration with XML. This allows interoperability with a wide range of existing infrastructures and across deployments. Currently no strict security models and mechanisms are available that can provide specification and enforcement of security policies for XML documents. Such models are crucial in order to facilitate a secure dissemination of XML documents, containing information of different sensitivity levels, among (possibly large) user communities.