Multiparty Private Set Intersection Cardinality and Its Applications

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Presented at Privacy Enhancing Technologies Symposium 2024 by

Jiahui Gao

Ni Trieu

Avishay Yanai

We describe a new paradigm for multi-party private set intersection cardinality (PSI-CA) that allows 𝑛 parties to compute the intersection size of their datasets without revealing any additional information. We explore a variety of instantiations of this paradigm. By operating under the assumption that a particular subset of parties refrains from collusion, our protocols avoid computationally expensive public-key operations and are secure in the presence of a semi-honest adversary. We demonstrate the practicality of our PSI-CA with an implementation. For 𝑛 = 16 parties with data-sets of 2 20 items each, our server-aided variant takes 71 seconds. Interestingly, in the serverless setting, the same task takes only 7 seconds. To the best of our knowledge, this is the first ‘special purpose’ implementation of a multi-party PSI-CA from symmetric-key techniques (i.e. an implementation that does not rely on a generic underlying MPC). We study two interesting applications – heatmap computation and associated rule learning (ARL) – that can be computed securely using a dot-product as a building block. We analyse the performance of securely computing heatmap and A