基于密文策略属性加密的云存储访问控制方案

针对现有方案存在的访问策略公开、密文存储开销较大的问题，提出一种支持策略隐藏且固定长度密文的云存储访问控制方案，并在安全模型下证明方案可抵抗选择明文攻击。方案中用户私钥由多个授权机构共同生成，中央授权机构不参与生成任何主密钥与属性私钥；访问结构隐藏在密文之中，恶意用户无法通过访问结构获取敏感信息。此外，方案实现了固定密文长度，并且加密时的指数运算和解密时的双线性对运算次数均是固定值。最后，理论分析和实验结果表明该方案在密文长度和加解密时间上都明显优于对比方案。

A ciphertext-policy attribute-based encryption access control scheme for cloud storage

In order to solve the problems of exposed access policy and large storage overhead in existing schemes, this paper proposed an access control scheme with hidden policy and constant length ciphertext for cloud storage, and it has proved that the scheme can resist the chosen-plaintext attack under the security model. In this scheme, multiple authorities generated private keys for users, and the central authority did not participate in the generation of any master key or attribute private key. The access structure was hidden within the ciphertext, so that malicious users can not obtain sensitive information through the access structure. In addition, this scheme realized constant length ciphertext. The number of exponentiation operation for encryption and bilinear pairing operation for decryption were fixed. Finally, the theoretical analysis and experimental results show that our scheme is superior to the contrast schemes in ciphertext length and the time of encryption and decryption.