Querying Encrypted XML Documents

This paper proposes techniques to query encrypted XML documents. Such a problem predominantly occurs in "database as a service" (DAS) architectures, where a client may outsource data to a service provider that provides data management services. Security is of paramount concern, as the service provider itself may be untrusted. Encryption offers a natural solution to preserve the confidentiality of the client's data. The challenge now is to execute queries over the encrypted data, without decrypting them at the server side. In this paper we develop: 1) primitives using which a client can specify the sensitive parts of the XML documents; 2) mechanisms to map the XML documents to encrypted representation that hides sensitive portions of the documents; and 3) techniques to run SPJ (selection-projection-join) queries over encrypted XML documents. A strategy, where indices/ancillary information is maintained along with the encrypted XML documents is exploited, which helps in pruning the search space during query processing