  Security issues are the most challenging problems in cloud computing
environments as an emerging technology. Regarding to this importance, an
efficient and reliable user authentication and data protection model has been
presented in this paper to increase the rate of reliability cloud-based
environments. Accordingly, two encryption procedures have been established in
an independent middleware (Agent) to perform the process of user
authentication, access control, and data protection in cloud servers. AES has
been used as a symmetric cryptography algorithm in cloud servers and RSA has
been used as an asymmetric cryptography algorithm in Agent servers. The
theoretical evaluation of the proposed model shows that the ability of
resistance in face with possible attacks and unpredictable events has been
enhanced considerably in comparison with similar models because of using dual
encryption and an independent middleware during user authentication and data
protection procedures.
