  Privacy concerns in outsourced cloud databases have become more and more
important recently and many efficient and scalable query processing methods
over encrypted data have been proposed. However, there is very limited work on
how to securely process top-k ranking queries over encrypted databases in the
cloud. In this paper, we focus exactly on this problem: secure and efficient
processing of top-k queries over outsourced databases. In particular, we
propose the first efficient and provable secure top-k query processing
construction that achieves adaptively CQA security. We develop an encrypted
data structure called EHL and describe several secure sub-protocols under our
security model to answer top-k queries. Furthermore, we optimize our query
algorithms for both space and time efficiency. Finally, in the experiments, we
empirically analyze our protocol using real world datasets and demonstrate that
our construction is efficient and practical.
