Confidante: Usable Encrypted Email: A Case Study with Lawyers and Journalists

Email encryption tools remain underused, even by people who frequently conduct sensitive business over email, such as lawyers and journalists. Usable encrypted email has remained out of reach largely because key management and verification remain difficult. However, key management has evolved in the age of social media: Keybase is a service that allows users to cryptographically link public keys to their social media accounts (e.g., Twitter), enabling key trust without out-of-band communication. We design and prototype Confidante, an encrypted email client that uses Keybase for automatic key management. We conduct a user study with 15 people (8 U. S. lawyers and 7 U. S. journalists) to evaluate Confidante's design decisions. We find that users complete an encrypted email task more quickly and with fewer errors using Confidante than with an existing email encryption tool, and that many users report finding Confidante comparable to using ordinary email. However, we also find that lawyers and journalists have diverse operational constraints and threat models, and thus that there may not be a one-size-fits-all solution to usable encrypted email. We reflect on our findings — both specifically about Confidante and more generally about the needs and constraints of lawyers and journalists—to identify lessons and remaining security and usability challenges for encrypted email.