Touchscreen-based devices such as smartphones and tablets are gaining popularity, but their rich input capabilities pose new development and testing complications. To alleviate this problem, we present an approach and tool named Reran that permits record-and-replay for the Android smartphone platform. Existing GUI-level record-and-replay approaches are inadequate due to the expressiveness of the smartphone domain, in which applications support sophisticated GUI gestures, depend on inputs from a variety of sensors on the device, and have precise timing requirements among the various input events. We address these challenges by directly capturing the low-level event stream on the phone, which includes both GUI events and sensor events, and replaying it with microsecond accuracy. Moreover, Reran does not require access to app source code, perform any app rewriting, or perform any modifications to the virtual machine or Android platform. We demonstrate RERAN's applicability in a variety of scenarios, including (a) replaying 86 out of the Top-100 Android apps on Google Play; (b) reproducing bugs in popular apps, e.g., Firefox, Facebook, Quickoffice; and (c) fast-forwarding executions. We believe that our versatile approach can help both Android developers and researchers.

Android uses a system of permissions to control how apps access sensitive devices and data stores. Unfortunately, we have little understanding of the evolution of Android permissions since their inception (2008). Is the permission model allowing the Android platform and apps to become more secure? In this paper, we present arguably the first long-term study that is centered around both permission evolution and usage, of the entire Android ecosystem (platform, third-party apps, and pre-installed apps). First, we study the Android platform to see how the set of permissions has evolved; we find that this set tends to grow, and the growth is not aimed towards providing finer-grained permissions but rather towards offering access to new hardware features; a particular concern is that the set of Dangerous permissions is increasing. Second, we study Android third-party and pre-installed apps to examine whether they follow the principle of least privilege. We find that this is not the case, as an increasing percentage of the popular apps we study are overprivileged. In addition, the apps tend to use more permissions over time. Third, we highlight some concerns with pre-installed apps, e.g., apps that vendors distribute with the phone; these apps have access to, and use, a larger set of higher-privileged permissions which pose security and privacy risks. At the risk of oversimplification, we state that the Android ecosystem is not becoming more secure from the user's point of view. Our study derives four recommendations for improving the Android security and suggests the need to revisit the practices and policies of the ecosystem.

The Android platform lacks tools for assessing and monitoring apps in a systematic way. This lack of tools is particularly problematic when combined with the open nature of Google Play, the main app distribution channel. As our key contribution, we design and implement ProfileDroid, a comprehensive, multi-layer system for monitoring and profiling apps. Our approach is arguably the first to profile apps at four layers: (a) static, or app specification, (b) user interaction, (c) operating system, and (d) network. We evaluate 27 free and paid Android apps and make several observations: (a) we identify discrepancies between the app specification and app execution, (b) free versions of apps could end up costing more than their paid counterparts, due to an order of magnitude increase in traffic, (c) most network traffic is not encrypted, (d) apps communicate with many more sources than users might expect---as many as 13, and (e) we find that 22 out of 27 apps communicate with Google during execution. ProfileDroid is the first step towards a systematic approach for (a) generating cost-effective but comprehensive app profiles, and (b) identifying inconsistencies and surprising behaviors.