Title: Toward Usable Access Control for End-users
Description: Many protection mechanisms in computer security are designed to enforce a configurable policy. The security policy captures high-level goals and intentions, and is managed by a policy author tasked with translating these goals into an implementable policy. In our work, we focus on access control policies where errors in the specified policy can result in the mechanism incorrectly denying a request to access a resource, or incorrectly allowing access to a resource that they should not have access to. Due to the need for correct policies, it is critical that organizations and individuals have usable tools to manage security policies. Policy management encompasses several subtasks including specifying the initial security policy, modifying an existing policy, and comprehending the effective policy. The policy author must understand the configurable options well enough to accurately translate the desired policy into the implemented policy. Specifying correct security policies is known to be a difficult task, and prior work has contributed policy authoring tools that are more usable than the prior art and other work has also shown the importance of the policy author being able to quickly understand the effective policy.

Specifying a correct policy is difficult enough for technical users, and now, increasingly, end-users are being asked to make access control decisions in regard to who can access their personal data. We focus on the need for an access control mechanism that is usable for end-users. We investigated end-users who are already managing an access control policy, namely social network site (SNS) users. We first looked at how they manage the access control policy that defines who can access their shared content. We accomplish this by empirically evaluating how Facebook users utilize the available privacy controls to implement an access control policy for their shared content and found that many users have policies are inconsistent with their sharing intentions. Upon discovering that many participants claim they will not take corrective action in response to inconsistencies in their existing settings, we collected quantitative and qualitative data to measure whether SNS users are concerned with the accessibility of their shared content.

After confirming that users do in fact care about who accesses their content, we hypothesize that we can increase the correctness of users' SNS privacy settings by introducing contextual information and specific guidance based on their preferences. We found that the combination of viewership feedback, a sequence of direct questions to audit the user's sharing preferences, and specific guidance motivates some users to modify their privacy settings to more closely approximate their desired settings. Our results demonstrate the weaknesses of ACL-based access control mechanisms, and also provide support that it is possible to improve the usability of such mechanisms. We conclude by outlining the implications of our results for the design of a usable access control mechanism for end-users.