Signcryption is a useful cryptographic primitive which simultaneously performs encryption and signature with cost less than the signature-then-encryption approach. Identity-based signcryption (IBSC) eliminates the complicated management of certificates in signcryption schemes in the traditional public-key infrastructure (PKI) setting. Most IBSC schemes are constructed in the random oracle model, while it is unknown how to instantiate a really "random" oracle in the real world. By exploiting Boneh et al.'s strongly unforgeable signature and Paterson et al.'s identity-based signature, this paper proposes a new IBSC scheme in the standard model. It is proven that our IBSC scheme satisfies semantic security and strong unforgeability under the bilinear decision Diffie-Hellman (BDDH) assumption. The proofs do not rely on random oracles. Performance analysis shows that our scheme is also efficient and practical.
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