In cloud computing distributed resources are shared via network in open environment. Hence user can easily access their data from anywhere. At the same time there exist privacy and security issues due to many reasons. First one is dramatic development in network technologies. Another is increased demand for computing resources, which make many organizations to outsource their data storage. So there is a need for secure cloud storage service in public cloud environment where the provider is not a trusted one. This paper addresses different data security and privacy protection issues in a cloud computing environment and proposes a method for providing different security services like authentication, authorization and confidentiality along with monitoring in delay. 128 bit Advanced Encryption Standard (AES) is used for increase data security and confidentiality. In this proposed approach data is encrypted using AES and then uploaded on a cloud. The proposed model uses Short Message Service (SMS) alert mechanism for avoiding unauthorized access to user data.