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Users struggle to select strong passwords. System-assigned passwords address this problem, but they can be difficult for users to memorize. While password managers can help store system-assigned passwords, there will always be passwords that a user needs to memorize, such as their password manager’s master password. As such, there is a critical need for research into helping users memorize system-assigned passwords. In this work, we compare three different designs for password memorization aids inspired by the method of loci or memory palace. Design One displays a two-dimensional scene with objects placed inside it in arbitrary (and randomized) positions, with Design Two fixing the objects’ position within the scene, and Design Three displays the scene using a navigable, three-dimensional representation. In an A-B study of these designs, we find that, surprisingly, there is no statistically significant difference between the memorability of these three designs, nor that of assigning users a passphrase to memorize, which we used as the control in this study. However, we find that when perfect recall failed, our designs helped users remember a greater portion of the encoded system-assigned password than did a passphrase, a property we refer to as durability. Our results indicate that there could be room for memorization aids that incorporate fuzzy or error-correcting authentication. Similarly, our results suggest that simple (i.e., cheap to develop) designs of this nature may be just as effective as more complicated, high-fidelity (i.e., expensive to develop) designs. 

Two-factor authentication (2FA) defends against account compromise by protecting an account with both a password—the primary authentication factor—and a device or resource that is hard to steal—the secondary authentication factor (SAF). However, prior research shows that users need help registering their SAFs with websites and successfully enabling 2FA. To address these issues, we propose the concept of a SAF manager that helps users manage SAFs through their entire life cycle: setup, authentication, removal, replacement, and auditing. We design and implement two proof-of-concept prototypes. In a between-subjects user study (N=60), we demonstrate that our design improves users' ability to correctly and quickly setup and remove a SAF on their accounts. Qualitative results show that users responded very positively to the SAF manager and were enthusiastic about its ability to help them rapidly replace a SAF. Furthermore, our SAF manager prevented fatal errors that users experienced when not using the manager. 

Current revocation strategies have numerous issues that prevent their widespread adoption and use, including scalability, privacy, and new infrastructure requirements. Consequently, revocation is often ignored, leaving clients vulnerable to man-in-the-middle attacks. This paper presents Let's Revoke, a scalable global revocation strategy that addresses the concerns of current revocation checking. Let's Revoke introduces a new unique identifier to each certificate that serves as an index to a dynamically-sized bit vector containing revocation status information. The bit vector approach enables significantly more efficient revocation checking for both clients and certificate authorities. We compare Let's Revoke to existing revocation schemes and show that it requires less storage and network bandwidth than other systems, including those that only cover a fraction of the global certificate space. We further demonstrate through simulations that Let's Revoke scales linearly up to ten billion certificates, even during mass revocation events.