Abstract: The popularity and widespread use of cloud have brought great convenience for data sharing and collection. Not only can individuals acquire useful data more easily, sharing data with others can provide a number of benefits to our society. Due to its openness, data sharing is always deployed in a hostile environment and vulnerable to a number of security threats. Taking energy usage data sharing, there are several security goals a practical system must meet. By providing security of data in a cloud we can convert data into unknown format and stored into cloud. In this paper we are proposed mainly three concepts for performing authentication of data consumers, generation of group key and provide security of sharing data in cloud. By performing authentication of data consumers we can implement the concepts for identity based digital signature. By using this concept we can verify users are authenticated or not. After completion of authentication process the cloud will generate group key and send to all group members. By using that secret key each data consumer will retrieve data from the cloud and get original plain format. Before getting original plain format data each users will perform the decryption process. In this paper we are using blowfish encryption and decryption algorithm for converting data into unknown format and get original data by using decryption process. So that by implementing those concepts we can provide more security of data and also provide efficient user authentication.

Keywords: Cloud Computing, Security, Encryption, Decryption, Authentication.