Approximate private information retrieval

Abstract

We present efficient protocols for the 1-out-of-n single-server Computationally-Private Information Retrieval (CPIR) problem for l-bit strings. In particular, our results achieve simultaneously polylogarithmic extra storage, communication, and Client and Server local computational complexities, improving the best current bounds. Most designs for CPIR exploit the communication vs. computation trade-off, whereas ours exploit instead trade-offs between accuracy and the metrics mentioned above. The work is of a theoretical nature. In a nutshell, our polylogarithmic claims show that it is possible to substantially reduce the mentioned complexity measures at the expense of accuracy of the results. The main indirect (practical) implication of this work is to show that CPIR is actually viable for very large databases. We also present some open questions and future directions.