With the rapid development of the cloud computing, the concepts of cloud computing technology have been applied gradually in many high-tech industries. There are many applications of cloud computing, and among them, cloud storage service is one of the best known because of its extensive utilization in people's daily lives. The use of cloud storage services eliminates the need for people to purchase heavy, expensive devices to provide the large storage space required for their data. Instead, they only need a networked device, which allows them to store their data in the cloud storage server and access the data anywhere. Therefore, more and more people are using the cloud storage server, and this is accompanied by an increasing number of security issues. In this paper, we proposed a secure protocol for the cloud storage service system. Analyses showed that our proposed protocol can withstand potential attacks and that it possesses essential functionalities, such as user anonymity, data dynamics, and data integrity. Therefore, our proposed protocol is suitable for practical implementation. Copyright © 2014 John Wiley & Sons, Ltd.