Reflex: Faster Secure Collaborative Analytics via Controlled Intermediate Result Size Disclosure

Abstract

Secure Multi-Party Computation (MPC) enables collaborative analytics without exposing private data. However, OLAP queries under MPC remain prohibitively slow due to oblivious execution and padding of intermediate results with filler tuples. We present Reflex, the first framework that enables configurable trimming of intermediate results across different query operators -- joins, selections, and aggregations -- within full query plans. At its core is the Resizer operator, which can be inserted between any oblivious operators to selectively remove filler tuples under MPC using user-defined probabilistic strategies. To make privacy trade-offs interpretable, we introduce a new metric that quantifies the number of observations an attacker would need to infer the true intermediate result sizes. Reflex thus makes the performance-privacy space of secure analytics navigable, allowing users to balance efficiency and protection. Experiments show substantial runtime reductions while maintaining quantifiable privacy guarantees.