Designing and implementing secure and usable graphical password methods

Authentication with a username and password is very common in applications which require secure access. Security precautions on data transmission and on infrastructure are meaningless if users select weak passwords. This means that there is a great demand for both usable and secure authentication methods.In this thesis we investigate graphical password schemes which were proposed as alternatives to text based authentication systems. The fact that people recall images better than verbal or textual knowledge suggests that graphical password systems could be successful. On the other hand, it is very difficult to provide security and usability simultaneously for systems that involve human interaction. The literature on graphical password schemes presents new and improved designs. However, changing habits of people is a challenging process. In this thesis we put forward a new idea to bring graphical passwords into practical usage. We developed an open-source browser extension which facilitates the use of graphical passwords on all web applications without a need to change the traditional text based password scheme implemented on servers. We have chosen one of the successful schemes i.e., PassPoints and investigated appropriateness of its usage in our development environment by conducting experiments. Then we proposed new schemes GPI and GPIS and conducted usability and security experiments. One of the main purposes of our studies is to find a usable and secure graphical password scheme so that users can use in practice and can generate passwords which are easy to remember but hard to guess.Keywords: graphical password, security, usable security, authentication