为了解决传统公钥密码体制中的证书管理问题和身份基公钥密码体制中的密钥托管问题，Al-Riyami和Paterson 提出了无证书公钥密码体制。最近朱辉等提出了一个不含双线性对运算的无证书签密机制。然而，通过对其进行分析，发现该机制是不安全的（即不能提供保密性和不可伪造性），并给出了具体的攻击方法。为了增强安全性，提出了一个更安全的无证书签密机制，并在随机预言模型下基于离散对数问题和计算性Diffie-Hellman问题给出了安全性证明。此外，新机制具有良好的性能，签密算法只需要4个模幂运算，解密验证算法只需要5个模幂运算。%To solve the certificate management problem in the traditional public key cryptography and the key escrow problem in the identity-based public key cryptography, Al-Riyami and Paterson proposed the concept of the certificateless public key cryptography. Recently, Zhuet al. proposed a certificateless signcryption without bilinear pairings. However, their scheme was completely insecure against with two concrete attacks. A strongly secure certificateless signcryption without bilinear pairings was also proposed, which was provably secure in the random oracle model under the assumption that the discrete logarithm problem and the computational Diffie-Hellman problems were intractable. Furthermore, the efficiency of the proposed scheme is very high since only four modular exponentiations and five modular exponentiations are needed in the signcryption algoriahm and unsigncryption algorithm separately.
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