H2ORAM: Low Response Latency Optimized ORAM for Hybrid Memory Systems

Emerging Non-Volatile Memory (NVM) techniques suffer from many attacks on endurance and data confidentiality. Oblivious RAM (ORAM) can prevent both types of attacks by address obfuscation and encryption. However, ORAM also introduces a lot of redundant memory operations, worsening the NVM endurance and system performance. Furthermore, the slower NVM increases the response latency of target blocks compared to DRAM. As the read requests are on the critical path of program execution, the increased latency further reduces system performance. To alleviate endurance and performance problems, we propose H ₂ ORAM, a low response latency optimized ORAM scheme for NVM. Hybrid DRAM/NVM system is introduced to eliminate 57% read/write traffic to NVM, which improves the lifetime of NVM devices. To reduce response latency of read requests, we securely manipulate data distributions in hybrid memory to speed up hot data access. The manipulation leverages a frequency-based eviction scheme and a data duplication scheme to keep more hot data accessible from DRAM earlier and faster. Moreover, we utilize the empty slots in DRAM region to further improve performance. The experimental results show that 44% response latency reduction and 18% performance improvement are achieved over the basic Ring ORAM with hybrid memory architecture integrated.