Applications of doubly efficient private information retrieval

Abstract

We have entered an era when most data has been outsourced to a potentially untrusted server. In this setting, even with encryption, the physical location accessed, or access patterns, during a query can reveal significant information about the query or database. This motivates the development of techniques to conceal access patterns, such as Private Information Retrieval (PIR) and Oblivious RAM (ORAM). Both allow retrieval of database item without revealing which item is retrieved at a sub-linear (often polylog) communication/computation cost to the client. ORAM requires the client to have a secret key and the server to keep state, but gets sub-linear (even log) server computation and allows both reads and writes. PIR does not require any client secret and the server is stateless, but requires linear server computation. This motivated the development of Doubly Efficient Private Information Retrieval (DEPIR) by Canetti et al. [CHR'17] and Boyle et al. [BIPW'17]. DEPIR allows a client to interact with a single stateless server and achieve overhead (both bandwidth and server computation) that is sub-linear in the database size. In this thesis, we explore three applications of DEPIR in the outsourced data setting, and tradeoffs that lie between ORAM and PIR. We leverage DEPIR's inherent statelessness and sub-linearity to achieve applications that neither PIR nor ORAM could accomplish. First we will explore a variant of ORAM, Rewindable ORAM (RORAM) that leverages DEPIR's statelessness to maintain security even when an adversary resets client and server state. RORAM is required to create the first heuristic construction of Fully Homomorphic Encryption in the RAM model. Our second application considers secure computation in the RAM model, using DEPIR's sub-linear server work to construct a distributed ORAM with constant rounds and sub-linear server work. Finally, we use techniques from DEPIR to achieve a multi-client private and anonymous data access scheme called PANDA.--Author's abstract