Toward Privacy-Assured Cloud Data Services with Flexible Search Functionalities

User privacy has been a major concern against the widespread adoption of the cloud technology. A full-fledged cloud data service should effectively support data utilization tasks, especially flexible data search functionalities, while simultaneously achieve user privacy assurance and meet practical system-level performance requirements. In this position paper, we identify the importance and challenges of designing privacy-assured, textit{flexible} and textit{practically efficient} search mechanisms for outsourced cloud data services. In particular, we focus on two representative types of flexible search functionalities: ranked keyword search, and search over structured data. Although these functionalities are already prevalent in information retrieval in the plaintext domain, realizing them in the encrypted domain requires non-trivial effort and is relatively new. In light of this, we first describe several existing technical approaches proposed by us and other researchers, and identify their advantages and limitations. We also discuss the open research directions and provide some possible ideas for further investigation. We believe the presented results will inspire more research towards making privacy-assured search in the cloud practical and useful.