Iranian Society of Cryptology The ISC International Journal of Information Security 2008-2045 Articles in Press 2025 12 26 Efficient Pairing-Free Adaptable k-out-of-n Oblivious Transfer Protocols 14 28 237327 10.22042/isecure.2025.237327 EN Keykhosro Khosravani Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran Taraneh Eghlidos Electronics Research Institute, Sharif University of Technology, Tehran, Iran 0000-0002-3182-0277 Mohammad Reza Aref Information Systems and Security Lab (ISSL), Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran Journal Article Oblivious Transfer (OT) is one of the fundamental building blocks in cryptography that enables various privacy-preserving applications. Constructing efficient OT schemes has been an active research area. This paper presents three efficient two-round pairing-free k-out-of-n oblivious transfer protocols with standard security. Our constructions follow the minimal communication pattern: the receiver sends k messages to the sender, who responds with n+k messages, achieving the lowest data transmission among pairing-free k-out-of-n OT schemes. Furthermore, our protocols support adaptivity and enable the sender to encrypt the n messages offline, independent of the receiver’s variables, offering significant performance advantages in one-sender-multiple-receiver scenarios. We provide security proofs under the Computational Diffie-Hellman (CDH) and RSA assumptions, without relying on the Random Oracle Model. Our protocols combine minimal communication rounds, adaptivity, offline encryption capability, and provable security, making them well-suited for privacy-preserving applications requiring efficient oblivious transfer.  https://www.isecure-journal.com/article_237327_9344cf7d20225736bca7607bd9f0a4c3.pdf