Paper 2021/1440

Improved Circuit-based PSI via Equality Preserving Compression

Abstract

Circuit-based private set intersection (circuit-PSI) enables two parties with input set $X$ and $Y$ to compute a function $f$ over the intersection set $X \cap Y$, without revealing any other information. State-of-the-art protocols for circuit-PSI commonly involves a procedure that securely checks whether two input strings are equal and outputs an additive share of the equality result. This procedure is typically performed by generic two party computation protocols, and its cost occupies quite large portion of the total cost of circuit-PSI. In this work, we propose {\textit{equality preserving compression}} (EPC) protocol that compresses the length of equality check targets while preserving equality using homomorphic encryption (HE) scheme, which is secure against the semi-honest adversary. This can be seamlessly applied to state-of-the-art circuit-PSI protocol frameworks. We demonstrate by implementation that our EPC provides $10-40\%$ speed-up for circuit-PSI with set size from $2^{16}$ to $2^{20}$, on LAN network. We believe that EPC protocol itself can be independent interest, which can be applied to other application than PSI.