Based on the characteristics and data security requirements of the cloud environment, we present a scheme for a multi-security-level cloud storage system that is combined with AES symmetric encryption and an improved identity-based proxy re-encryption (PRE) algorithm. Our optimization includes support for fine-grained control and performance optimization. Through a combination of attribute-based encryption methods, we add a fine-grained control factor to our algorithm in which each authorization operation is only valid for a single factor. By reducing the number of bilinear mappings, which are the most time-consuming processes, we achieve our aim of optimizing performance. Last but not least, we implement secure data sharing among heterogeneous cloud systems. As shown in experiment, our proposed multi-security-level cloud storage system implements services such as the direct storage of data, transparent AES encryption, PRE protection that supports fine-grained and ciphertext heterogeneous transformation, and other functions such as authentication and data management. In terms of performance, we achieve time-cost reductions of 29.8% for the entire process, 48.3% for delegation and 47.2% for decryption.

中文翻译：

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基于改进的代理重新加密的多安全级别云存储系统

基于云环境的特征和数据安全性要求，我们提出了一种多安全级别的云存储系统方案，该方案与AES对称加密和改进的基于身份的代理重新加密（PRE）算法相结合。我们的优化包括对细粒度控制和性能优化的支持。通过组合基于属性的加密方法，我们在算法中添加了细粒度的控制因子，其中每个授权操作仅对单个因子有效。通过减少最耗时的双线性映射的数量，我们达到了优化性能的目的。最后但并非最不重要的一点是，我们在异构云系统之间实现了安全的数据共享。如实验所示，我们提议的多安全级别的云存储系统可实现服务，例如数据的直接存储，透明AES加密，支持细粒度和密文异构转换的PRE保护以及其他功能，例如身份验证和数据管理。在性能方面，我们将整个过程的时间成本减少了29.8％，委派减少了48.3％，解密减少了47.2％。