Compass: Encrypted Semantic Search with High Accuracy

We present Compass, a semantic search system for encrypted data that achieves high accuracy, matching state-ofthe-art plaintext search quality, while ensuring the privacy of data, queries, and results, even if the server is compromised. Compass contributes a novel way to traverse a state-of-the-art graph-based semantic search index and a white-box co-design with Oblivious RAM, a cryptographic primitive that hides access patterns, to enable efficient search over encrypted embeddings. With our techniques, Directional Neighbor Filtering, Speculative Neighbor Prefetch, and Graph-Traversal Tailored ORAM, Compass achieves user-perceived latencies within or around a second and is orders of magnitude faster than baselines under various network conditions.