ObliviSync: Practical Oblivious File Backup and Synchronization

TL;DR

ObliviSync is a practical, efficient oblivious cloud storage system that protects user data and access patterns during synchronization and backup, achieving near-optimal performance and security against timing attacks.

Contribution

We introduce ObliviSync, a novel write-only ORAM-based system optimized for personal cloud storage, providing practical efficiency and security features not previously available.

Findings

Achieves approximately 4x overhead compared to non-private storage.

Supports multiple read-only clients and a single read/write client.

Operates effectively under high workloads with minimal latency increase.

Abstract

Oblivious RAM (ORAM) protocols are powerful techniques that hide a client's data as well as access patterns from untrusted service providers. We present an oblivious cloud storage system, ObliviSync, that specifically targets one of the most widely-used personal cloud storage paradigms: synchronization and backup services, popular examples of which are Dropbox, iCloud Drive, and Google Drive. This setting provides a unique opportunity because the above privacy properties can be achieved with a simpler form of ORAM called write-only ORAM, which allows for dramatically increased efficiency compared to related work. Our solution is asymptotically optimal and practically efficient, with a small constant overhead of approximately 4x compared with non-private file storage, depending only on the total data size and parameters chosen according to the usage rate, and not on the number or size of individual files. Our construction also offers protection against timing-channel attacks, which has not been previously considered in ORAM protocols. We built and evaluated a full implementation of ObliviSync that supports multiple simultaneous read-only clients and a single concurrent read/write client whose edits automatically and seamlessly propagate to the readers. We show that our system functions under high work loads, with realistic file size distributions, and with small additional latency (as compared to a baseline encrypted file system) when paired with Dropbox as the synchronization service.