我们提出了两个有效的抗选择密文攻击的基于身份门限解密方案。在标准的决定性双线性Diffie-Hellman假设下，它们被证明可以抗选择密文攻击。第一个方案基于Boneh 和Boyen 提出的一个Selective IBE方案，另外一个方案基于Waters提出的Full IBE方案。与所基于的方案相同，前者的挑战身份要在公共参数选取之前确定，而后者的挑战身份可以由攻击者适应性地选取。据我们所知，以前的相关方案的安全性只能在随机预言机模型中得以证明。

We propose two efficient Identity-Based threshold decryption schemes They are proved secure against chosen ciphertext attacks under the standard decisional bilinear Diffie-Hellman assumption. The first one is constructed from (one of ) the Selective ID-Based Encryption (Selective-IBE) scheme proposed by Boneh and Boyen recently, yet the second one is transformed from the Full ID-Based Encryption (Full-IBE) scheme obtained by Waters. As the based IBE schemes, the attacker in the first proposal has to choose the challenge identity before the common parameter is generated, while the attacker in the second one could choose the identity adaptively. To the best of our knowledge, previous related schemes could only be proved secure in the random oracle model.