支持撤销的外包加解密CP-ABE方案

属性基加密（attribute-based encryption，ABE）方案在云存储中得到了越来越广泛的应用，它能够实现细粒度的访问控制，但是现有的大多数ABE方案存在撤销方案效率低、开销大的问题。为了解决这一问题，提出一种更高效、细粒度的支持属性撤销的属性基加密方案。该方案将部分加解密运算外包给代理服务器，从而降低用户的加解密计算量。同时还提出了一种有效的属性撤销方法，该方法只需更新与撤销属性相关联的密文和用户密钥，所以属性撤销的代价很小。并结合了双因子身份认证机制，提高算法的安全性。该方案基于DBDH假设，在标准模型下被证明是安全的。

Outsourcing encryption and decryption CP-ABE scheme with revocation

ABE scheme has been more and more widely used in cloud storage, it can achieve fine-granularity access control. However, most of the existing ABE schemes have the problems of low efficiency and high overhead. In order to solve this problem, this paper proposed a more efficient and fine-grained attribute-based encryption scheme supporting attribute revocation. The transfers the complex computation of the encryption and decryption process to the proxy server, thus reducing the encryption and decryption computation of users. This paper also proposed an efficient attribute revocation method which concentrated on the update of the ciphertexts and users'' secret keys associated with the corresponding revoked attributes, so the cost of attribute revocation is very small. And combined the method of two-factor identity authentication to improve the security of the algorithm. The theoretical analysis show that this scheme is safe under the standard model based on the DBDH hypothesis.