Security and its subcategory authentication are among the important subjects of cloud computing. In this system, user authentication mechanisms are carried out before providing access to resources. It is noteworthy that this input gate is actually the pathway of many attacks. Therefore, designing a secure user authentication mechanism significantly contributes to the overall security of the system. This process blocks attacks where the objective is to authenticate a user and when the user requests for cloud computing services. As a result, this article aimed to introduce a new security solution for cloud computing environments through employing the EAP-TTLS protocol, replacing the common Data Encryption Algorithm (DEA) with a new one, and adding a digital signature to the authentication process. After implementation of the proposed method in matlab, its performance was evaluated with RSA and ECDSA algorithms. The results of simulation showed the improvement of performance in terms of memory usage, authentication time, and verification delay. The proposed method [digital signature], along with username and password, is used to improve security in user authentication process.