Crust: Verifiable And Efficient Private Information Retrieval with Sublinear Online Time

Private Information Retrieval (PIR) is a cryptographic primitive that enables a user to retrieve information from a database without revealing the particular information they are seeking, thus preserving their privacy. PIR schemes suffer from high computation overhead. By running an offline preprocessing phase, PIR schemes can achieve sublinear online server computation. On the other hand, although protocols for honest-but-curious servers have been well-studied in both single-server and multi-server scenarios, little work has been done for the case where the server is malicious. In this paper, we propose a simple but efficient sublinear PIR scheme named Crust. The scheme is tailored for verifiability and provides privacy and data integrity against malicious servers. Our scheme can work with two servers or a single server. Aside from verifiability, our scheme is very efficient. Compared to state-of-the-art two-server and single-server sublinear PIR schemes, our scheme is 22x more efficient in online computation. To the best of our knowledge, this is the first PIR scheme that achieves verifiability, as well as amortized $O(\sqrt{n})$ server computation