Download PDFOpen PDF in browserSecurity Analysis on a Public-Key Inverted-Index Keyword Search Scheme with Designated Tester9 pages•Published: August 21, 2025AbstractGao et al. (IEEE Internet of Things Journal 2024) proposed public-key inverted-index keyword search with designated tester as an extension of public key encryption with keyword search (PEKS). In their scheme, a server (a tester) has a secret key and uses the key for running the search algorithm due to the designated tester setting. They proved that no information of keyword is revealed from trapdoors under the decisional Diffie-Hellman (DDH) assumption. However, they also employed a symmetric pairing which can be seen as a DDH-solver. Thus, it is expected that information of keyword is revealed from trapdoors since the underlying complexity assumption does not hold. In this paper, we demonstrate an attack against the Gao et al.'s scheme where information of keyword is revealed from a trapdoor. Our attack completes by using only the server's secret key in addition to the challenge trapdoor, without any additional encryption/trapdoor queries, and the attack complexity is just two pairing computations. We remark that an adversary is not allowed to obtain the server's secret key in their security model, and our attack is outside of their security model. Thus, we discuss the roles of the server, and stress that our attack scenario is reasonable.Keyphrases: ddh, designated tester, public key encryption with keyword search, symmetric pairing In: Akira Yamada, Huy Kang Kim, Yujue Wang and Tung-Tso Tsai (editors). Proceedings of the 20th Asia Joint Conference on Information Security, vol 106, pages 31-39.
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