An improved semantically-secure identity-based signcryption scheme in the standard model

Recently, Yu et al. proposed the first identity-based signcryption scheme without random oracles and proved it was semantically secure in the standard model. However, in this paper we find that their scheme actually does not reach the semantic security as they claimed. To make up for this defect, we propose a rescue scheme and show our improvement is really secure in the standard model based on the intractability of the Decisional Bilinear Diffie–Hellman assumption.