Graphical Password Schemes

As mentioned earlier, our evaluation is based on two graphical schemes. In the Face scheme, the password is a collection of $k$ faces, each selected from a distinct set of $n > 1$ faces. Each of the $n$ faces are chosen uniformly at random from a set of faces classified as belonging to either a ``typical'' Asian, black or white male or female, or an Asian, black or white male or female model. This categorization is further discussed in Section 3.1. For our evaluation we choose $k = 4$ and $n = 9$. So, while choosing her password, the user is shown four successive $3 \times 3$ grids containing randomly chosen images (see Figure 1, for example), and for each, she selects one image from that grid as an element of her password. Images are unique and do not appear more than once for a given user. During the authentication phase, the same sets of images are shown to the user, but with the images randomly permuted.

Figure 1: In the Face scheme, a user's password is a sequence of $k$ faces, each chosen from a distinct set of $n > 1$ faces like the one above. Here, $n = 9$, and images are placed randomly in a $3 \times 3$ grid.

In the Story scheme, a password is a sequence of $k$ unique images selected by the user to make a ``story'', from a single set of $n > k$ images, each derived from a distinct category of image types. The images are drawn from categories that depict everyday objects, food, automobiles, animals, children, sports, scenic locations, and male and female models. A sample set of images for the story scheme is shown in Figure 2.

Figure 2: In the Story scheme, a user's password is sequence of $k$ unique images selected from one set of $n$ images, shown above, to depict a ``story''. Here, $n = 9$, and images are placed randomly in a $3 \times 3$ grid.