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