A High-Performance Oblivious RAM Controller on the Convey HC-2ex Heterogeneous Computing Platform

In recent work published at ACM CCS 2013 [5], we introduced Phantom, a new secure processor that obfuscates its memory access trace. To an adversary who can observe the processor’s output pins, all memory access traces are computationally indistinguishable (a property known as obliviousness). We achieve obliviousness through a cryptographic construct known as Oblivious RAM or ORAM. Existing ORAM algorithms introduce a fundamental overhead by having to access significantly more data per memory access (i.e. cache miss): this overhead is 100-200× or more, making ORAM inefficient for real-world workloads. In Phantom, we exploit the Convey HC-2ex heterogeneous computing platform – a system consisting of an off-the-shelf x86 CPU paired with 4 high-end FPGAs and a highly parallel memory system – to reduce ORAM access latency. We present a novel ORAM controller that aggressively exploits the HC-2ex’s high DRAM bank parallelism to reduce ORAM access latency and scales well to a large number of memory channels. Phantom is efficient in both area and performance: accessing 4KB of data from a 1GB ORAM takes 26.2us (13.5us until the data is available), a 32× slowdown over accessing 4KB from regular memory, while SQLite queries on a population database see 1.2-6× slowdown.