Updatable Private Set Intersection with Low Communication Overhead

Private set intersection (PSI) is a fundamental cryptographic task that allows two mutually distrusting parties, each holding a private set of elements, to jointly compute the intersection of their sets. It ensures a symmetric information structure where neither party gains any knowledge about the other’s elements beyond those in the shared intersection. Traditional PSI protocols are primarily designed for static settings, which limits their applicability and efficiency in dynamic scenarios where input sets continuously evolve. To address this challenge, the notion of updatable PSI (UPSI) was introduced, enabling repeated PSI computations over changing inputs while preserving the symmetric privacy guarantees between participants. Despite the numerous recent advancements in UPSI research, it still suffers from significant communication overhead. In this paper, we address this challenge by introducing LcUPSI (low-communication UPSI), a new updatable PSI protocol that achieves remarkably low communication overhead. We formally prove that LcUPSI is secure in the semi-honest model. Furthermore, we compare the LcUPSI protocol with the state-of-the-art UPSI protocol BMSTZ24 (ASIACRYPT). The results demonstrate that LcUPSI significantly reduces communication overhead, highlighting its advantages in low-bandwidth conditions.