In this paper, we propose an advanced implementation of Path ORAM to hide the access pattern to outsourced data into the cloud. This implementation takes advantage of eventual data locality and popularity by introducing a small amount of extra storage at the client side. Two replacement strategies are used to manage this extra storage (cache): the Least Recently Used (LRU) and the Least Frequently Used (LFU). Using the same test bed, conducted experiments clearly show the superiority of the advanced implementation compared to the traditional Path ORAM implementation, even for a small cache size and reduced data locality. We then present a mathematical model that provides closed form solutions when data requests follow a Zipf distribution with non-null parameter. This model is showed to have a small and acceptable relative error and is then well validated by the conducted experimental results.

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.

Oblivious Random-Access Memory (ORAM) is becoming a fundamental component for modern outsourced storages as a cryptographic primitive to prevent information leakage from a user access pattern. The major obstacle to its proliferation has been its significant bandwidth overhead. Recently, several works proposed acceptable low-overhead constructions, but unfortunately they are only evaluated using algorithmic complexities which hide valuable constants that severely impact their practicality. Four of the most promising constructions are Path ORAM, Ring ORAM, XOR Ring ORAM, and Onion ORAM. However, they have never been thoroughly compared against each other and tested on the same experimental platform. To address this issue, we provide a thorough study and assessment of these recent ORAM constructions and implement them under the same testbed. We perform extensive experiments to provide insights into their performance characteristics, simplicity, and practicality in terms of processing time, server storage, client storage, and communication cost. Our extensive experiments show that despite the claimed algorithmic efficiency of Ring and Onion ORAMs and their judicious limited bandwidth requirements, Path ORAM stands out to be the simplest and most efficient ORAM construction.

No abstract