Billions of people currently use the Internet. Many Internet users share sensitive information through online services. Several secure data sharing tools have been developed to protect this sensitive information. A common practice in the design of usable security is to provide automatic data encryption that is transparent to users. We hypothesize that automatic encryption can decrease usability and comprehensibility, increasing the likelihood that users will unknowingly disclose sensitive information. This thesis presents Message Protector (MP), a novel Internet secure data sharing tool design that through manual encryption, purposely exposes technical details in a usable manner to increase usability and reduce mistakes. We have developed a rapid prototype that we used to evaluate MP usability via cognitive walkthrough and two usability studies. In the studies, we compared the MP prototype with existing secure data sharing tools. The results of the user studies demonstrate that MP design increases usability, user comprehension, and the likelihood of successful use.

Billions of web-based email and chat messages are sent over the Internet every day. However, very few service providers support end-to-end privacy protection. While providing security for these messages is technically feasible, usability remains a challenge in this field. Recent research attempts to hide security details like key management and encryption in order to make the system more usable. However usability studies demonstrated that hiding these details may confuse the user and contribute to mistakes (e.g., sending out an email in plaintext when the user thought it would be encrypted). In an effort to increase trust and eliminate mistakes, this thesis presents the design of a browser-based manual encryption mechanism that supports automatic key-management and manual encryption. It also describes the Message Protector (MP) prototype. An evaluations of MP is presented based on a user study conducted on the campus of BYU.