Keywords: Identity Based Encryption, Identity Based Signature, Identity Based Signcryption
In this paper, we show how to construct an Identity Based Signcryption Scheme (IBSC) using anIdentity Based Encryption (IBE) and an Identity Based Signature (IBS) schemes. This we obtain byfirst extending the An-Dodis-Rabin construction to the Identity Based setting and then instantiating.We then further modify the construction to obtain an efficient construction. We show that the securityof the IBSC scheme–indistinguishability as well as unforgeablity–is derived from the security of theunderlying IBE and IBS schemes. Moreover, we show that under mild (reasonable) assumptions, thescheme is both space and time efficient compared to the Sign-then-Encrypt approach.