中文摘要：

云存储中，代理重加密技术可以保障用户数据在存储第三方的安全性和可共享性。该技术的核心思想是：数据拥有者以密文形式将数据存储在第三方；数据拥有者可以委托存储第三方对其存储的密文进行重加密并共享给其他用户。该文提出了一种类型可修改的基于身份代理重加密方案，该方案不仅具有传统代理重加密方案的核心功能，而且密文的拥有者可以随时修改密文的信息类型。在实际应用中，该方案比基于类型和身份的代理重加密方案具有更加广泛的应用场景。

英文摘要：

Cloud storage is drawing tremendous attention in IT field. In it, an open challenge is to keep the privacy of users’ outsourced data and securely share users’ data. To address this challenge, proxy re-encryption （PRE） scheme is one of promising method. A dynamic type and identity-based PRE scheme will be proposed. This scheme not only obtains the traditional functions of PRE, but also allows a user to update the original types of his outsourced ciphertexts. Compared with the previous PRE scheme, the new feature makes the proposed PRE scheme more useful in practical applications.