Hiding tree structured data and queries from untrusted data stores

With the increasing use of Web services, many new challenges concerning data security are becoming critical. Especially in mobile services, where clients are generally thin in terms of computation power and storage space, a remote server can be outsourced for the computation or can act as a data store. Unfortunately, such a data store may not always be trustworthy, and clients with sensitive data and queries may want protection from malicious attacks. This article presents a technique to hide tree-structured data from potentially malicious data stores, while allowing clients to traverse the data to locate an object of interest without leaking information to the data store. The two motivating applications for this approach are hiding (1) tree-like XML data as well as XML queries that are in the form of tree-paths, and (2) tree-structured indexes and queries executed on such data structures. We show that this task is achievable through a one-server protocol that introduces only a limited and adjustable communication overhead. This is especially essential in low-bandwidth (such as wireless) distributed environments. The proposed protocol has desirable communication and concurrency performance, as demonstrated by the experiments we have conducted.