Insider-secure Hybrid Signcryption SchemeWithout Random Oracles

Confidentiality and authenticity are two important security requirements in most secure systems. To efficiently provide data privacy (confidentiality) and (data/user) authenticity simultaneously, the notion of signcryption scheme was first introduced by Zheng in 1997. The security model for signcryption scheme was proposed by Baek et al. and An et al. in 2002 independently. Since then, many signcryption schemes were proposed; they are either a public-key signcryption or a hybrid signcryption. But, only few proposed signcryption schemes were supposed to be in the insider security, for example, Libert-Quisquater´s signcryption schemes at PKC´2004 and SCN´2004 respectively and Yang-Wong-Deng´s signcryption scheme at ISC´2005. Although all the above mentioned signcryption schemes were proved insider-secure against adaptive chosen ciphertext attack in the random oracle models, Tan showed that all the above mentioned signcryption schemes were not insider-secure against adaptive chosen ciphertext attack in 2005 and 2006 respectively. Up to our knowledge, it seems that none of insider-secure hybrid signcryption scheme is constructed without random oracles. In this paper, we proposed a hybrid signcryption scheme and showed that the proposed scheme is insider-secure without random oracles