“Say I'm in public...I don't want my nudes to pop up.” User Threat Models for Using Vault Applications

Vault apps and hidden albums are tools used to encrypt and hide sensitive photos, videos, and other files. While security researchers have analyzed how technically secure they are, there is little research to understand how and why users use vault apps, and whether these tools meet their needs. To understand user threat models for vault apps, we conducted semi-structured interviews (N = 18) with U.S. adult vault app users. We find our participants store intimate media, nonsexual body images, photos of partying and drinking, identification documents, and other sensitive files. Participants primarily used vault apps to prevent accidental content exposure from shoulder surfing or phone sharing, whether in public or with and around close ties. Vault apps were not used to prevent a technically proficient adversary from accessing their files. We find that vault apps prevent context collapse when sharing devices, similar to how privacy settings prevent context collapse on social media. We conclude with recommendations for research aligning with user threat models, and design recommendations for vault apps.