International Association
for Cryptologic Research

Oblivious RAM (ORAM) is a security-provable approach for protecting clients' access patterns to remote cloud storage. Recently, numerous ORAM constructions have been proposed to improve the communication efficiency of the ORAM model, but little attention has been paid to the storage efficiency. The state-of-the-art ORAM constructions have the storage overhead of $O(N)$ or $O(N\log N)$ blocks at the server, when $N$ data blocks are hosted. To fill the blank, this paper proposes a storage-efficient ORAM (SE-ORAM) construction with configurable security parameter $\lambda$ and zero storage overhead at the server. Extensive analysis has also been conducted and the results show that, SE-ORAM achieves the configured level of security, introduces zero storage overhead to the storage server (i.e., the storage server only storages $N$ data blocks), and incurs $O(\log N)$ blocks storage overhead at the client, as long as $\lambda\geq 2$ and each node on the storage tree stores $4\log N$ or more data blocks.