Efficient Sharing of Secure Cloud Storage Services

Suppose Bob, the boss in Company A, pays a secure cloud storage service and authorizes all the employees in that company to share such a service. There exists a user hierarchy: Bob is the user at the upper level and all the employees in the company are the users at the lower level. In this paper, we design and construct a scheme, which enables the user at the upper level to efficiently share the secure cloud storage services with all the users at the lower level. A sender can specify several users at the lower level as the recipients for a file by taking the number and public keys of the recipients as inputs of a hierarchical identity-based encryption algorithm, which enables only the user at the upper level, as well as the intended recipients, to decrypt the file using their own private keys. Using our scheme, the sender needs to encrypt a file only once, and store only one copy of the corresponding ciphertext in a ``cloud´´ communicating with none of the recipients while encrypting a file to multiple recipients. To our best knowledge, this paper is the first to realize the efficient sharing of the secure storage services in cloud computing.