Radix Path: A Reduced Bucket Size ORAM for Secure Cloud Storage

This paper proposes a novel version of path oblivious random access memory called radix path ORAM (R-Path ORAM) with a large root (radix) bucket size but a small fixed size for all the other buckets in the tree. A detailed analysis of the root bucket occupancy is conducted to provide a closed-form solution of the required root bucket size that maintains a negligible failure probability. The performance of the R-Path ORAM is evaluated and compared against the traditional Path ORAM using a unified platform. The conducted experiments clearly show that R-Path ORAM provides much lower server storage and average response time than the seminal Path ORAM. Furthermore, we propose a background eviction technique to eventually reduce the root bucket size and avoid system failure. The conducted experiments on the unified platform showed the usefulness and efficiency of the proposed two-way eviction technique in successfully reducing the root bucket size while incurring a very small overhead.