Abstract
The popularity of sharing data through cloud services has increased these days. As a result, the security of data sharing has become an important issue. The security mechanism has to ensure that the shared data would not be intercepted or altered by illegal members during transmission. A data sharing scheme for cloud services is proposed in this paper to achieve the following four security requirements: 1) forward secrecy and backward secrecy, 2) source authentication, 3) data integrity, and 4) confidentiality. In addition, message recovery is applied to improve the efficiency of encryption and signature computation. The computation cost is reduced by computing a common key for all data. Thus, the data owner only needs to encrypt the shared data once before sending it in this proposed scheme.