Efficient Encrypted Data Search with Expressive Queries and Flexible Update

Outsourcing encrypted data to cloud servers that has been become a prevalent trend among Internet users to date. There is a long-list advantages of data outsourcing, such as the reduction cost of local data management. How to securely operate encrypted data (remotely), however, is the top-rank concern of data owner. Recently, Liang et al. proposed a novel encrypted cloud-based data share and search system without loss of privacy. The system allows users to flexibly search and share encrypted data as well as updating keyword field. However, the search complexity of the system is very inefficient, O(n d), where d is the total number of the system files and n is the size of query formula. This paper, for the first time, leverages the “oblivious cross search” technology in public key searchable encryption context to reduce the search complexity to only O(nf(w)), where f(w) is the number of files embedded with the “least frequent keyword” w. The new scheme maintains efficient encrypted data share and keyword field update as well. This paper further revisits the security models for payload security, keyword privacy and search token privacy (i.e. search pattern privacy) and meanwhile, presents security and efficiency analysis for the new scheme.