A multi-recipient signcryption scheme of strong security

This paper defines a strong security model for multi-recipient signcryption scheme in the random oracle model,which is semantically secure against adaptive chosen-ciphertext insider attack,existentially forgeable chosen-message attack and anonymous chosen-ciphertext insider attack.By analyzing,we point out that Li-Hu-Liu Multi-Recipient Signcryption Scheme is insecure against the adaptive and anonymous chosen-ciphertext insider attacks.Later,we present an improved scheme,which is proven to be secure in our newly defined strong security model.