Paper 2018/005

Simple and Efficient Two-Server ORAM

S. Dov Gordon, Jonathan Katz, and Xiao Wang

Abstract

We show a protocol for two-server oblivious RAM (ORAM) that is simpler and more efficient than the best prior work. Our construction combines any tree-based ORAM with an extension of a two-server private information retrieval scheme by Boyle et al., and is able to avoid recursion and thus use only one round of interaction. In addition, our scheme has a very cheap initialization phase, making it well suited for RAM-based secure computation. Although our scheme requires the servers to perform a linear scan over the entire data, the cryptographic computation involved consists only of block-cipher evaluations. A practical instantiation of our protocol has excellent concrete parameters: for storing an $$-element array of arbitrary size data blocks with statistical security parameter $$, the servers each store $$ encrypted blocks, the client stores $$ blocks, and the total communication per logical access is roughly $$ encrypted blocks.