Practical Searching over Encrypted Data by Private Information Retrieval

Explosive progress in networking and outsourcing storage increases the use of information retrieval technologies, in massive datasets. Nowadays, there are varieties of storage-providers through the internet, such as e-mail accounts and public database, which are convenient to store and exchange electronic files and medias. Typically, the storage-provider offers users the capability to collect, retrieve and search, however, privacy issues are rarely considered at the same time. For example, it is unknown how to prevent some curious storage- provider from learning the private information of the user, such as, searching criterion and access pattern, as well as contents. In CRYPTO´07, Boneh et al. put forward a privacy-preserving solution to this problem, with the help of public key cryptography. In their work, the authors made use of PIR (Private Information Retrieval) and several combinatoric techniques, which are theoretically interesting and likely to be the best approach in the literature. In this paper, however, we show that their proposal seems unlikely to be implementable with the latest technology, due to a large amount of computation cost involved. Then, we provide an improved method to turn the keyword search more practical, which cannot only avoid the expensive computation cost caused by operations of public key encryption, but enable the privacy-preserving information retrieval, as well.