针对已有的密文共享方案存在客户端计算量过大、用户管理密钥过多、不支持个人共享等问题,将公有云引入到密文共享方案的设计之中,提出一种面向公有云的安全文件共享框架.基于该框架设计了一种面向公有云的密文共享方案.该方案将绝大多数计算和存储都外包给公有云,用户只需保存两个空间占用很小的私钥子项且客户端只需进行少量计算即可完成共享文件的解密.安全分析结果表明,该方案不仅能够对抗恶意用户的合谋攻击,而且在一般群模型和随机预言模型下能够对抗选择明文攻击.“,”In view of the existing ciphertext sharing scheme, there is too large calculation of user clients, and each user manages too many secret keys. Moreover, it does not support personal sharing and other issues. Thus the Public Cloud is introduced into the ciphertext sharing scheme, and a security file-sharing framework of the Public Cloud is proposed. And based on this framework, a new ciphertext sharing scheme is designed. In this scheme, the vast majority of computation and storage are outsourced to the Public Cloud. The user simply saves two private key components occupying small space. The client only needs a little computation to complete encryption and decryption of the shared file. The security analysis shows that the scheme can deal with not only the conspiracy attack from malicious users, but also the plaintext-chosen attack in the generic group model and the random oracle model.