D-ORAM: Path-ORAM Delegation for Low Execution Interference on Cloud Servers with Untrusted Memory

Cloud computing has evolved into a promising computing paradigm. However, it remains a challenging task to protect application privacy and, in particular, the memory access patterns, on cloud servers. The Path ORAM protocol achieves high-level privacy protection but requires large memory bandwidth, which introduces severe execution interference. The recently proposed secure memory model greatly reduces the security enhancement overhead but demands the secure integration of cryptographic logic and memory devices, a memory architecture that is yet to prevail in mainstream cloud servers. In this paper, we propose D-ORAM, a novel Path ORAM scheme for achieving high-level privacy protection and low execution interference on cloud servers with untrusted memory. D-ORAM leverages the buffer-on-board (BOB) memory architecture to offload the Path ORAM primitives to a secure engine in the BOB unit, which greatly alleviates the contention for the off-chip memory bus between secure and non-secure applications. D-ORAM upgrades only one secure memory channel and employs Path ORAM tree split to extend the secure application flexibly across multiple channels, in particular, the non-secure channels. D-ORAM optimizes the link utilization to further improve the system performance. Our evaluation shows that D-ORAM effectively protects application privacy on mainstream computing servers with untrusted memory, with an improvement of NS-App performance by 22.5% on average over the Path ORAM baseline.