CAOS: Concurrent-Access Obfuscated Store

This paper proposes Concurrent-Access Obfuscated Store (CAOS), a construction for remote data storage that provides access-pattern obfuscation in a honest-but-curious adversarial model, while allowing for low bandwidth overhead and client storage. Compared to other approaches, the main advantage of CAOS is that it supports concurrent access without a proxy, for multiple read-only clients and a single read-write client. Concurrent access is achieved by letting clients maintain independent maps that describe how the data is stored. Even though the maps might diverge from client to client, the protocol guarantees that clients will always have access to the data. Efficiency and concurrency are achieved at the expense of perfect obfuscation: in CAOS the extent to which access patterns are hidden is determined by the resources allocated to its built-in obfuscation mechanism. To assess this trade-off we provide both a security and a performance analysis of CAOS. We additionally provide a proof-of-concept implementation available at https://github.com/meehien/caos.