An Improvement of an Identity-Based Key-insulated Signcryption

As one of the fundamental cryptographic primitives, signcryption can achieve unforgeability and confidentiality simultaneously at the cost significantly lower than the signature-then-encryption approach in terms of computational costs and communication overheads. In view of the damage caused by the secret key leakage, Chen et al. proposed an efficient identity-based key-insulated signcryption (ID-KI-SC) scheme secure in the standard model recently. However, in this paper, we show that their scheme does not achieve the indistinguishability against adaptively chosen ciphertext attacks (IND-CCA2) and existential unforgeability against adaptively chosen message attacks (EUF-CMA). Furthermore, we propose an improved scheme that remedies the weakness of Chen et al.’s scheme.

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