Identity based signcryption scheme without random oracles

Many identity based signcryption schemes have been proposed so far. However, all the schemes were proven secure in the random oracle model which has received a lot of criticism that the proofs in the random oracle model are not proofs. In this paper, motivated by Waters' identity based encryption scheme, we propose the first identity based signcryption scheme without random oracles. We prove that the proposed scheme is secure in the standard model. Specifically, we prove its semantic security under the hardness of Decisional Bilinear Diffie–Hellman problem and its unforgeability under the Computational Diffie–Hellman assumption.