Efficient identity based signature/signcryption scheme in the standard model

Identity based cryptosystem is a public key cryptosystem where the public key can be represented as an arbitrary string. However an identity based signature scheme that is fully secure in the standard model with a tight reduction has not been proposed until now. In this paper, we propose an identity based signature scheme that is fully secure in the standard model and has several advantages-computational efficiency, short public parameters, and a tight security reduction. In many situations we want to enjoy confidentiality and authenticity simultaneously. A traditional approach to achieve this objective is to "sign-then-encrypt" this message, or we can employ special cryptographic scheme like signcryption. To the best of our knowledge, reference [15] proposes the only identity based signcryption scheme in the standard model. But its security proof is based on a weaker model-" sample-ID" model and the reduction is not tight. Combining an identity based encryption scheme, we also propose the first identity based signcryption scheme that is fully secure in the standard model with a tight reduction. Moreover, our signcryption scheme has public verifiability.