A security assessment of tiles: a new portfolio-based graphical authentication system.

In this paper we propose Tiles, a graphical authentication system in which users are assigned a target image and subsequently asked to select segments of that image. We assess the extent to which this system provides protection against two security threats: observation attacks and sharing of authentication credentials in two laboratory-based studies. We note some of the vulnerabilities of the new system but provide evidence that automated manipulation of the similarity of the decoy images can help mitigate the threat from verbal sharing and observation attacks.