Context-sensitive guidance (CSG) can help users make better security decisions. Applications with CSG ask the user to provide relevant context information. Based on such information, these applications then decide or suggest an appropriate course of action. However, users often deem security dialogs irrelevant to the tasks they are performing and try to evade them. This paper contributes two new techniques for hardening CSG against automatic and false user answers. Polymorphic dialogs continuously change the form of required user inputs and intentionally delay the latter, forcing users to pay attention to security decisions. Audited dialogs thwart false user answers by (1) warning users that their answers will be forwarded to auditors, and (2) allowing auditors to quarantine users who provide unjustified answers. We implemented CSG against email-borne viruses on the Thunderbird email agent. One version, CSG-PD, includes CSG and polymorphic dialogs. Another version, CSG-PAD, includes CSG and both polymorphic and audited dialogs. In user studies, we found that untrained users accept significantly less unjustified risks with CSG-PD than with conventional dialogs. Moreover, they accept significantly less unjustified risks with CSG-PAD than with CSG-PD. CSG-PD and CSG-PAD have insignificant effect on acceptance of justified risks.

Existing Web browsers handle security errors in a manner that often confuses users. In particular, when a user visits a secure site whose certificate the browser cannot verify, the browser typically allows the user to view and install the certificate and connect to the site despite the verification failure. However, few users understand the risk of man-in-the-middle attacks and the principles behind certificate-based authentication. We propose context-sensitive certificate verification (CSCV), whereby the browser interrogates the user about the context in which a certificate verification error occurs. Considering the context, the browser then guides the user in handling and possibly overcoming the security error. We also propose specific password warnings (SPW) when users are about to send passwords in a form vulnerable to eavesdropping. We performed user studies to evaluate CSCV and SPW. Our results suggest that CSCV and SPW can greatly improve Web browsing security and are easy to use even without training. Moreover, CSCV had greater impact than did staged security training.

We introduce the notion of a conditioned-safe ceremony. A “ceremony ” is similar to the conventional notion of a protocol, except that a ceremony explicitly includes human participants. Our formulation of a conditioned-safe ceremony draws on several ideas and lessons learned from the human factors and human reliability community: forcing functions, defense in depth, and the use of human tendencies, such as rule-based decision making. We propose design principles for building conditioned-safe ceremonies and apply these principles to develop a registration ceremony for machine authentication based on email. We evaluated our email registration ceremony with a user study of 200 participants. We designed our study to be as ecologically valid as possible: we employed deception, did not use a laboratory environment, and attempted to create an experience of risk. We simulated attacks against the users and found that email registration was significantly more secure than challenge question based registration. We also found evidence that conditioning helped email registration users resist attacks, but contributed towards making challenge question users more vulnerable. 1

The Windows Vista personal firewall provides its diverse users with a basic interface that hides many operational details. However, concealing the impact of network context on the security state of the firewall may result in users developing an incorrect mental model of the protection provided by the firewall. We present a study of participants ’ mental models of Vista Firewall (VF). We investigated changes to those mental models and their understanding of the firewall’s settings after working with both the VF basic interface and our prototype. Our prototype was designed to support development of a more contextually complete mental model through inclusion of network location and connection information. We found that participants produced richer mental models after using the prototype than when working with the VF basic interface; they were also significantly more accurate in their understanding of the configuration of the firewall. Based on our results, we discuss methods of improving user understanding of underlying system states by revealing hidden context, while considering the tension between complexity of the interface and security of the system.

Support for strong electronic mail security is widely available yet only few communicants appear to make use of these features. Apparently, the operational overhead of security outweighs its perceived benefits. Towards increasing the benefits versus overhead ratio we follow an approach that considers security and usability tradeoffs from the outset. We separate key exchange from binding keys to identities. The best effort key exchange and key maintainance scheme that we devise operates transparently for the user. We also describe complementary visualization and interaction techniques that communicate the security state of sent and received mail to users in a non-intrusive fashion. Towards a practical assessment of the overheads of binding keys to identities, we conducted a quantitative analysis of users’ mail behavior of which we present the results. We argue that for individual non-commercial users, out-of-band verification of keys could be more economical than building trust in public key certificates issued by third parties.

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