Paper 2026/1153

Search-Efficient Public-Key Authenticated Encryption with Keyword Search Made Easy

Keita Emura, Kanazawa University, National Institute of Advanced Industrial Science and Technology

Abstract

Public-key authenticated encryption with keyword search (PAEKS), introduced by Huang and Li (Information Sciences 2017), was proposed to provide trapdoor privacy, whereby keyword information is protected from being revealed through trapdoors. To prevent the keyword guessing attack, however, a trapdoor needs to be generated separately for each sender, and the search complexity linearly grows with the number of senders even when searching for a single keyword. To address this inefficiency, we propose a generic construction of search-efficient PAEKS. We revisit the group-oriented approach of Wang et al. (IEEE Transactions on Information Forensics and Security 2024), in which senders are organized into sender groups. Our construction is simple yet effective where all senders belonging to the same group share a single public-secret key pair, and the search complexity depends only on the number of sender groups rather than the number of individual senders. We further introduce ciphertext indistinguishability against insiders, which ensures that no keyword information is revealed from ciphertexts, even if they are generated by other members of the same sender group. We also take into account an impossibility result by Yoshida and Emura (IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2026), which shows that trapdoor privacy against sender-group members cannot be achieved in the scheme of Wang et al. To address this limitation, we introduce trapdoor indistinguishability against outsiders, which guarantees that no keyword information is revealed from trapdoors generated for non-group members. Our generic construction yields search-efficient group-oriented PAEKS schemes from pairings and lattices.