Android's trust-on-first-use application signing model associates developers with a fixed code signing certificate, but lacks a mechanism to enable transparent key updates or certificate renewals. The model allows application updates to be recognized as authorized by a party with access to the original signing key. However, changing keys or certificates requires that end users manually uninstall/reinstall apps, losing all non-backed up user data. In this paper, we show that with appropriate OS support, developers can securely and without user intervention transfer signing authority to a new signing key. Our proposal, Baton, modifies Android's app installation framework enabling key agility while preserving backwards compatibility with current apps and current Android releases. Baton is designed to work consistently with current UID sharing and signature permission requirements. We discuss technical details of the Android-specific implementation, as well as the applicability of the Baton protocol to other decentralized environments.

Passwords continue to prevail on the web as the primary method for user authentication despite their well-known security and usability drawbacks. Password managers offer some improvement without requiring server-side changes. In this paper, we evaluate the security of dual-possession authentication, an authentication approach offering encrypted storage of passwords and theft-resistance without the use of a master password. We further introduce Tapas, a concrete implementation of dual-possession authentication leveraging a desktop computer and a smartphone. Tapas requires no server-side changes to websites, no master password, and protects all the stored passwords in the event either the primary or secondary device (e.g., computer or phone) is stolen. To evaluate the viability of Tapas as an alternative to traditional password managers, we perform a 30 participant user study comparing Tapas to two configurations of Firefox's built-in password manager. We found users significantly preferred Tapas. We then improve Tapas by incorporating feedback from this study, and reevaluate it with an additional 10 participants.