A new anti-spam protocol using CAPTCHA

Today sending spams has turned to be a major problem in the Internet. It is so serious that more than 80% of the transferred emails are spams. As a result, various methods have been proposed for preventing spams. One of these methods in this field is CAPTCHA (Completely Automatic Public Turing Test to tell Computer and Humans Apart) method. They have been developed to prevent automatically made accounts in sites which offer free email accounts. In this paper a new protocol is presented for authentication of users which enable us to confirm that a user is a human using CAPTCHA method. By using this protocol for authentication of users, we can design secure mail servers in order to prevent zombie computers sending spams by our server. This protocol has been designed according to CRAM-MD5 protocol and has been implemented under the SASL (Simple Authentication and Security Layer). This protocol can be implemented easily and enjoys high flexibility and versatility.