Insider-secure Signcryption KEM/Tag-KEM Schemes without Random Oracles

In this paper, we propose a signcryption key encapsulation (KEM) scheme and show that the proposed scheme is insider-secure against adaptive chosen ciphertext attack without random oracles and against strongly existential forgery without random oracles. In addition, by simple transformation of the proposed signcryption KEM scheme, we construct an insider-secure signcryption Tag- KEM scheme without random oracles, which responds to the calling from Yoshida and Fujiwara in 2007 on the construction of signcryption Tag-KEM scheme.