Certificateless Signcryption Scheme Without Random Oracles

Signcryption can realize encryption and signature simultaneously with lower computational costs and communication overhead than those of the traditional sign-then-encrypt approach. Certificateless cryptosystem solves the key escrow problem in the identity-based cryptosystem and simplifies the public key management in the traditional public key cryptosystem. So far there have been some certificateless signcryption schemes proposed in the standard model. However, they are either insecure or inefficient. They need long system public parameters, making it hard to deploy them in the limited storage environments. Based on the Gentry's identity-based encryption scheme, the authors propose a certificateless signcryption scheme in the standard model. Compared with previous schemes, the proposed scheme has not only much higher computational efficiency, but also shorter public parameters. The authors also give rigorous proof of its security.