Mind the Gap: Finding what Updates have (really) changed in Android Applications

Android apps often receive updates that introduce new functionality or tackle problems, ranging from critical security issues to usability-related bugs. Although developers tend to briefly denote changes when releasing new versions, it remains unclear what has actually been modified in the program code. Verifying even subtle changes between two Android apps is challenging due to the widespread use of code transformations and obfuscation techniques. In this paper, we present a new framework to precisely pinpoint differences between Android apps. By pursuing a multi-level comparison strategy that targets resources and obfuscation-invariant code elements, we succeed in highlighting similarities and changes among apps. In case studies, we demonstrate the need and practical benefits of our solution and show how well it is suited to verify changelogs.