Abstract-This paper presents an integrated evaluation of the Persuasive Cued Click-Points graphical password scheme, including usability and security evaluations, and implementation considerations. An important usability goal for knowledge-based authentication systems is to support users in selecting passwords of higher security, in the sense of being from an expanded effective security space. We use persuasion to influence user choice in click-based graphical passwords, encouraging users to select more random, and hence more difficult to guess, click-points.

Design of the user interface for authentication systems influences users and may encourage either secure or insecure behaviour. Using data from four different but closely related click-based graphical password studies, we show that user-selected passwords vary considerably in their predictability. Our post-hoc analysis looks at click-point patterns within passwords and shows that PassPoints passwords follow distinct patterns. Our analysis shows that many patterns appear across a range of images, thus motivating attacks which are independent of specific background images. Conversely, Cued Click-Points (CCP) and Persuasive Cued Click-Points (PCCP) passwords are nearly indistinguishable from those of a randomly-generated simulated dataset. These results provide insight on modeling effective password spaces and on how user interface characteristicsThe results of this paper first appeared in preliminary form as

Anecdotal evidence and scholarly research have shown that Internet users may regret some of their online disclosures. To help individuals avoid such regrets, we designed two modifications to the Facebook web interface that nudge users to consider the content and audience of their online disclosures more carefully. We implemented and evaluated these two nudges in a 6-week field trial with 28 Facebook users. We analyzed participants' interactions with the nudges, the content of their posts, and opinions collected through surveys. We found that reminders about the audience of posts can prevent unintended disclosures without major burden; however, introducing a time delay before publishing users' posts can be perceived as both beneficial and annoying. On balance, some participants found the nudges helpful while others found them unnecessary or overly intrusive. We discuss implications and challenges for designing and evaluating systems to assist users with online disclosures.

The underlying issues relating to the usability and security of multiple passwords are largely unexplored. However, we know that people generally have difficulty remembering multiple passwords. This reduces security since users reuse the same password for different systems or reveal other passwords as they try to log in. We report on a laboratory study comparing recall of multiple text passwords with recall of multiple click-based graphical passwords. In a one-hour session (short-term), we found that participants in the graphical password condition coped significantly better than those in the text password condition. In particular, they made fewer errors when recalling their passwords, did not resort to creating passwords directly related to account names, and did not use similar passwords across multiple accounts. After two weeks, participants in the two conditions had recall success rates that were not statistically different from each other, but those with text passwords made more recall errors than participants with graphical passwords. In our study, click-based graphical passwords were significantly less susceptible to multiple password interference in the short-term, while having comparable usability to text passwords in most other respects.

Password restriction policies and advice on creating secure passwords have limited effects on password strength. Influencing users to create more secure passwords remains an open problem. We have developed Persuasive Text Passwords (PTP), a text password creation system which leverages Persuasive Technology principles to influence users in creating more secure passwords without sacrificing usability. After users choose a password during creation, PTP improves its security by placing randomly-chosen characters at random positions into the password. Users may shuffle to be presented with randomly-chosen and positioned characters until they find a combination they feel is memorable. In this paper, we present an 83-participant user study testing four PTP variations. Our results show that the PTP variations significantly improved the security of users' passwords. We also found that those participants who had a high number of random characters placed into their passwords would deliberately choose weaker pre-improvement passwords to compensate for the memory load. As a consequence of this compensatory behaviour, there was a limit to the gain in password security achieved by PTP.