Oblivious Parallel RAM: Improved Efficiency and Generic Constructions

Oblivious RAM (ORAM) garbles read/write operations by a client (to access a remote storage server or a random-access memory) so that an adversary observing the garbled access sequence cannot infer any information about the original operations, other than their overall number. This paper considers the natural setting of Oblivious Parallel RAM (OPRAM) recently introduced by Boyle, Chung, and Pass (TCC 2016A), where m clients simultaneously access in parallel the storage server. The clients are additionally connected via point-to-point links to coordinate their accesses. However, this additional inter-client communication must also remain oblivious. The main contribution of this paper is twofold: We construct the first OPRAM scheme that (nearly) matches the storage and server-client communication complexities of the most efficient single-client ORAM schemes. Our scheme is based on an extension of Path-ORAM by Stefanov et al (CCS 2013). Moreover, we present a generic transformation turning any (single-client) ORAM scheme into an OPRAM scheme.