## Cryptology ePrint Archive: Report 2018/005

Simple and Efficient Two-Server ORAM

S. Dov Gordon and 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 $N$-element array of arbitrary size data blocks with statistical security parameter $\lambda$, the servers each store $4N$ encrypted blocks, the client stores $\lambda+2\log N$ blocks, and the total communication per logical access is roughly $10 \log N$ encrypted blocks.

Category / Keywords: cryptographic protocols / ORAM, single-round, multi-party computation, RAM model

Original Publication (in the same form): Asiacrypt 2018

Date: received 1 Jan 2018, last revised 5 Sep 2018

Contact author: wangxiao at cs umd edu

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2018/005

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