无双线性对的门限条件匿名代理重加密方案

条件代理重加密(CPRE)可以根据条件对密文进行细粒度的授权，现有的CPRE方案只检查原密文的条件，忽略了重加密密钥的条件符合性，也不对条件信息进行保护，容易造成隐私泄露。该文构造了基于门限的无双线性对条件匿名代理重加密方案(TB-CAPRE)，对密文和重加密密钥的条件同时进行验证，并将敏感的条件信息进行匿名化处理，利用门限将重加密分布到多个代理节点完成，能够抵御合谋攻击。理论分析证明了该方案在随机预言模型下满足适应性选择密文攻击下的不可区分安全性(IND-CCA)。效率和计算量分析表明TB-CAPRE在增加安全性和相关功能后并没有引入过大的开销，可以应用到分布式环境中。

Threshold- Based Pairing-free Conditional Anonymous Proxy Re-Encryption Scheme

Conditional Proxy Re-Encryption (CPRE) can grant fine-grained authorization to the original ciphertext according to the conditions. The existing CPRE schemes only check the conditions of the original ciphertext, but ignore the conditions of the re-encryption key. No effective measures are taken to protect the conditions in these CPRE schemes, which may lead to privacy disclosure of conditions. A Threshold-Based Conditional Anonymous Proxy Re-Encryption scheme (TB-CAPRE) is constructed, which can not only verify the conditions of ciphertext and re-encryption key at the same time, but also make sensitive conditional information anonymous. The re-encryption processes are completed by multiple agent nodes, so TB-CAPRE can resist the collusion attacks. The theoretical analysis proves that the new scheme is INDistinguishable against adaptive Chosen-Ciphertext Attack(simply donoted by IND-CCA) in the random oracle. The analysis of performance and computation shows that TB-CAPRE does not introduce excessive overhead while increasing security and related functions. It is possible that TB-CAPRE is applied to distributed environment.