User Authentication Scheme using Session Passwords based on Color and Numerical Matrix

User authentication is one of the principal topics in information security. Traditional strong password schemes could provide with certain degree of security; however, strong passwords being difficult to memorize often leads their owners to write them down on papers or even save them in a computer file. As a result, security becomes greatly weakened. Textual passwords are the most common method used for authentication. But textual passwords are vulnerable to eves dropping, dictionary attacks, social engineering and shoulder surfing. Graphical passwords are introduced as an alternative technique to textual passwords. Most of the graphical schemes are vulnerable to shoulder surfing. To address this problem, text can be combined with images or colors to generate session passwords for authentication. Multiple colors or images are used to confuse the peepers, while not burdening the legitimate users. Meanwhile, the scheme is resistant to shoulder surfing and intersection attack to a certain extent. Session passwords can be used only once and every time a new password is generated. In this paper, two techniques are proposed to generate session passwords using text and colors which are resistant to shoulder surfing. These methods are suitable for Personal Digital Assistants.