X.509 certificate revocation defends against man-in-the-middle attacks involving a compromised certificate. Certificate revocation strategies face scalability, effectiveness, and deployment challenges as HTTPS adoption rates have soared. We propose Certificate Revocation Table (CRT), a new revocation strategy that is competitive with or exceeds alternative state-of-the-art solutions in effectiveness, efficiency, certificate growth scalability, mass revocation event scalability, revocation timeliness, privacy, and deployment requirements. The CRT design assumes that locality of reference applies to the certificates accessed by an organization. The CRT periodically checks the revocation status of X.509 certificates recently used by the organization. Pre-checking the revocation status of certificates the clients are likely to use avoids the security problems of on-demand certificate revocation checking.

Secure email is increasingly being touted as usable by novice users, with a push for adoption based on recent concerns about government surveillance. To determine whether secure email is ready for grassroots adoption, we employ a laboratory user study that recruits pairs of novice users to install and use several of the latest systems to exchange secure messages. We present both quantitative and qualitative results from 28 pairs of novices as they use Private WebMail (Pwm), Tutanota, and Virtru and 10 pairs of novices as they use Mailvelope. Participants report being more at ease with this type of study and better able to cope with mistakes since both participants are “on the same page.” We find that users prefer integrated solutions over depot-based solutions and that tutorials are important in helping first-time users. Finally, our results demonstrate that Pretty Good Privacy using manual key management is still unusable for novice users, with 9 of 10 participant pairs failing to complete the study.

Two-factor authentication (2FA) significantly improves the security of password-based authentication. Recently, there has been increased interest in Universal 2nd Factor (U2F) security keys-small hardware devices that require users to press a button on the security key to authenticate. To examine the usability of security keys in non-enterprise usage, we conducted two user studies of the YubiKey, a popular line of U2F security keys. The first study tasked 31 participants with configuring a Windows, Google, and Facebook account to authenticate using a YubiKey. This study revealed problems with setup instructions and workflow including users locking themselves out of their operating system or thinking they had successfully enabled 2FA when they had not. In contrast, the second study had 25 participants use a YubiKey in their daily lives over a period of four weeks, revealing that participants generally enjoyed the experience. Conducting both a laboratory and longitudinal study yielded insights into the usability of security keys that would not have been evident from either study in isolation. Based on our analysis, we recommend standardizing the setup process, enabling verification of success, allowing shared accounts, integrating with operating systems, and preventing lockouts.