Remote Oblivious Storage: Making Oblivious RAM Practical

Remote storage of data has become an increasingly attractive and advantageous option, especially due to cloud systems. While encryption protects the data, it does not hide the access pattern to the data. A natural solution is to access remote storage using an Oblivious RAM (ORAM) which provably hides all access patterns. While ORAM is asymptotically efficient, the best existing scheme (Pinkas and Reinman, Crypto’10) still has considerable overhead for a practical implementation: for M stored items, it stores 4 times and sometimes 6 times more items remotely, requires O(log M) round trips to storage server per request, and periodically blocks all data requests to shuffle all storage (which is a lengthy process). In this paper, we first define a related notion to ORAM, oblivious storage (OS), which captures more accurately and naturally the security setting of remote storage. Then, we propose a new ORAM/OS construction that solves the practicality issues just outlined: it has a storage constant of ≈ 1, achieves O(1) round trips to the storage server per request, and allows requests to happen concurrently with shuffle without jeopardizing security. Our construction consists of a new organization of server memory into a flat main part and a hierarchical shelter, a client-side index for rapidly locating identifiers at the server, a new shelter serving requests concurrent with the shuffle, and a data structure for locating items efficiently in a partially shuffled storage.