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A temporal key management scheme for secure broadcasting of XML documents

Secure broadcasting of web documents is becoming a crucial need for many web-based applications. Under the broadcast document dissemination strategy a web document source periodically broad-casts (portions of) its documents to a possibly large community of subjects, without the need of explicit subject requests. By secure broadcasting we mean that the delivery of information to sub-jects must obey the access control policies of the document source. Since different subjects may have the right to access different portions of the same document, enforcing secure broadcasting requires to efficiently manage a large number of different physical views of the requested document and sending them to the proper subjects. In this paper we present an approach to secure broadcasting of web documents, based on the use of encryption techniques, and supporting the specification of fine-grained temporal access control policies. The idea is to generate a unique encrypted copy of the document to be released, where different portions of the docu-ment are encrypted with different keys, on the basis of the specified access control policies. Each subject then obtains the secret keys corresponding to document portions he/she is authorized to access. The key aspect of our approach is that the number of keys to be generated does not depend on the number of subjects nor on the document dimension, but only on the number of specified access control policies and the associated temporal constraints.