Sharing information to others is common nowadays, but the question is with whom to share. To address this problem, we propose the notion of secret transfer with access structure (STAS). STAS is a twoparty computation protocol that enables the server to transfer a secret to a client who satisfies the prescribed access structure. In this paper, we focus on threshold secret transfer (TST), which is STAS for threshold policy and can be made more expressive by using linear secret sharing. TST enables a number of applications including a simple construction of oblivious transfer (OT) with threshold access control, and (a variant of) threshold private set intersection (t-PSI), which are the first of their kinds in the literature to the best of our knowledge. The underlying primitive of STAS is a variant of OT, which we call OT for a sparse array. We provide two constructions which are inspired by state-of-the-art PSI techniques including oblivious polynomial evaluation (OPE) and garbled Bloom filter (GBF). The OPEbased construction is secure in the malicious model, while the GBF-based one is more efficient. We implemented the latter one and showed its performance in applications such as privacy-preserving matchmaking.
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