Cassandra: Towards a Certifying App Store for Android Modern mobile devices store and process an abundance of data. Although many users consider some of this data as private, they do not yet obtain satisfactory support for controlling what applications might do with their data. In this talk, we present Cassandra, a certifying app store that enables users of mobile devices to check whether Android apps comply with their personal privacy requirements before installing these apps. In more detail, we describe the design and implementation of Cassandra, as well as the formal foundation of its underlying security analysis.