On Hiding Access Timings in ORAM

Oblivious RAM (ORAM) is a cryptographic primitive for hiding access patterns in cloud environments. Though the ordinary security definition of ORAM guarantees indistinguishability between access sequences of the same length, it cannot be guaranteed for access sequences of different lengths. Hence, ORAM cannot hide access timings or frequency. In this paper, we propose an ORAM scheme that can hide access timings. First, we extend the ordinary security definition. We formulate the hiding property of access timings by defining indistinguishability between access sequences of different lengths. Furthermore, we introduce a new ORAM scheme by adapting the dummy access technique. We prove that our scheme is secure in the proposed definition.