PSImple: Practical Multiparty Maliciously-Secure Private Set

Private set intersection (PSI) protocols allow a set of mutually distrustful parties, each holding a private set of items, to compute the intersection over all their sets, such that no other information is revealed. PSI has a wide variety of applications including online advertising (e.g., efficacy computation), security (e.g., botnet detection, intrusion detection), proximity testing (e.g., COVID-19 contact tracing), and more. Private set intersection is a rapidly developing area and there exist many highly efficient protocols. However, almost all of these protocols are for the case of two parties or for semi-honest security. In particular, despite the high interest in this problem, prior to our work there has been no concretely efficient, maliciously secure multiparty PSI protocol. We present PSImple, the first concretely efficient maliciously-secure multiparty PSI protocol. Our construction is based on oblivious transfer and garbled Bloom filters, and has a round-optimal online phase. To demonstrate the practicality of PSImple, we implemented it and ran experiments with up to 32 parties and 2 20 inputs. We show that PSImple is competitive even with the state-of-the-art concretely efficient semi-honest multiparty PSI protocols. Additionally, we revisit the garbled Bloom filter parameters used in the 2-party PSI protocol of Rindal and Rosulek (Eurocrypt 2017). Using a more careful analysis, we show that the size of the garbled Bloom filters and the number of oblivious transfers required for malicious security can be significantly reduced, often by more than 20%. These improved parameters also imply a better security guarantee, and can be used both in the 2-party PSI protocol of Rindal and Rosulek and in i>PSImple.