Fully Secure Identity Based Key-Insulated Signcryption in the Standard Model

To achieve unforgeability and confidentiality simultaneously, signcryption has been introduced with better efficiency than the signature-then-encryption approach in terms of computational costs and communication overheads. Taking the key leakage into account, it is desirable to design identity-based key-insulated signcryption (ID-KI-SC) scheme to reduce the damage caused by the secret key leakage. In this paper, we have shown that all of the existing ID-KI-SC scheme can not offer either the unforgeability property or the indistinguishability property. Furthermore, an improved scheme along with the formal security proof in the standard model has been suggested in this paper. In view of computational cost and communication overhead, our scheme is amongst the most efficient IB-SC schemes secure in the standard model.