在随机预言模型下定义了一个多接收者签密方案的强安全性模型，该模型满足适应性选择密文内部攻击安全性、选择消息抗存在性伪造和密文匿名安全性；通过分析指出, Li、Hu和Liu等人提出的多接收者签密方案, 不具有适应性选择密文内部攻击安全性和密文匿名性，并给出所定义强安全性模型中的攻击方法；随后提出改进方案，该方案在强安全模型中证明是安全的。

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.