Efficient 3-Party Distributed ORAM.

Distributed Oblivious RAM (DORAM) protocols—in which parties obliviously access a shared location in a shared array—are a fundamental component of secure-computation protocols in the RAM model. We show here an efficient, 3-party DORAM protocol with semi-honest security for a single corrupted party. To the best of our knowledge, ours is the first protocol for this setting that runs in constant rounds, requires sublinear communication and linear work, and makes only black-box use of cryptographic primitives. Our protocol also appears to be concretely more efficient than existing solutions. As a building block of independent interest, we construct a 3-server distributed point function (DPF) with security against two colluding servers that is arguably simpler and has better concrete efficiency than prior work. We also show how to distribute the key-generation protocol of this DPF (in a black-box manner).