Towards a metric for recognition-based graphical password security

Recognition-based graphical password (RBGP) schemes are not easily compared in terms of security. Current research uses many different measures which results in confusion as to whether RBGP schemes are secure against guessing and capture attacks. If it were possible to measure all RBGP schemes in a common way it would provide an easy comparison between them, allowing selection of the most secure design. This paper presents a discussion of potential attacks against recognition-based graphical password (RBGP) authentication schemes. As a result of this examination a preliminary measure of the security of a recognition-based scheme is presented. The security measure is a 4-tuple based on distractor selection, shoulder surfing, intersection and replay attacks. It is aimed to be an initial proposal and is designed in a way which is extensible and adjustable as further research in the area develops. Finally, an example is provided by application to the PassFaces scheme.