中文摘要：

组合公钥方案是一种用于基于身份密码体制中生成用户加密密钥和私钥的知名方案。针对组合公钥方案存在合谋攻击的问题，通过仅扩展该方案的私钥生成过程，实现了扩展方案的抗合谋攻击性．在此基础上构建标准模型下基于Decisional Bilinear Diffie—Hellman假设可证明安全的一种新的基于身份加密方案．最后，为了说明所构新方案的实用性，分析了扩展组合公钥方案的用户加密密钥抗碰撞性；对比了新方案和同类的3个知名方案在安全性证明的归约程度方面、加解密的时间复杂度方面和密文的长度方面的性能，表明了新方案在以上3点上具有目前最优的指标．因此新方案是相对较实用的．

英文摘要：

The Combined Public-Key scheme is a famous scheme which is commonly used to generate user＇s encryption-key and private-key in the identity-based encryption schemes. For over- coming the conspiracy attack on Combined Public-Key scheme, a new expanded scheme based on it is proposed in which the generation of private-key is an expansion of the corresponding part of combined public-key scheme. Based on the new expanded Combined Public-Key scheme, a new identity-based encryption scheme is proposed, and under the standard model it is provably secure based on Decisional Bilinear Diffie-Hellman Assumption. At last, by analyzing the collision of user＇s encryption-key and comparing the new proposed identity-based encryption scheme with three existed famously analogous schemes at the following three aspects： the tightness of reduc- tion in security proof, the complexity of encryption and decryption and the binary length of ciphertext, it can be found that the new scheme is more efficient than them, so it is comparatively more useful.