Private information retrieval (PIR) is a cryptographic technique that enables users to fetch records from untrusted and remote database servers without revealing to those servers which particular records are being fetched. This talk will discuss "indexes of queries", a novel mechanism for supporting efficient, expressive, and information-theoretically private single-round queries over multi-server PIR databases. The indexes of queries approach decouples the way that users construct their requests for data from the physical layout of the remote data store, thereby enabling users to fetch data using "contextual" queries that specify /which/ data they seek, as opposed to the more common "positional" queries that specify /where/ those data happen to reside within the database. For example, a Twitter-like microblogging service could employ indexes of queries to let users fetch "the 5 most recent tweets by @CSL_Illinois" or "the 10 top trending tweets for hashtag #UIUC". Our basic approach is compatible with any PIR protocol in the ubiquitous "vector-matrix" model for PIR, though the most sophisticated and useful of our constructions rely on some nice algebraic properties of Goldberg's Shamir-based IT-PIR protocol (Oakland 2007). We have implemented our techniques as an extension to Percy++, an open-source implementation of Goldberg's IT-PIR protocol. Our experiments indicate that the new techniques can greatly improve not only utility for private information retrievers but also efficiency for private information retrievers and servers alike.
Ryan Henry is an assistant professor in the Computer Science Department at Indiana University in Bloomington, Indiana. His research explores the systems challenges of applied cryptography, with an emphasis on using cryptography to build secure systems that preserve the privacy of their users. In addition to designing and analyzing privacy-enhancing systems, Professor Henry is interested in practical matters like implementing and working toward the deployment of such systems, as well as more theoretical matters like devising number-theoretic attacks against non-standard cryptographic assumptions and developing new models and theories to understand just how efficient "heavy-weight" cryptographic primitives can be. He received his MMath (2010) and Ph.D. (2014) from the University of Waterloo, where he held a Vanier Canada Graduate Scholarship (Vanier CGS), the most prestigious graduate scholarship in Canada. He has published several papers on PIR at top research venues (e.g., CCS, NDSS, and PETS), is a contributor to Percy++ (an open-source implementation of PIR protocols in C++), and two of his three active NSF grants heavily involve PIR research.