The permissions framework for Android is frustratingly inflexible. Once granted a permission, Android will always allow an app to access the resource until the user manually revokes the app's permission. Prior work has proposed extensible plugin frameworks, but they have struggled to support flexible authorization and isolate apps and plugins from each other. In this paper, we propose DALF, a framework for extensible permissions plugins that provides both flexibility and isolation. The insight underlying DALF is that permissions plugins should be treated as apps themselves. This approach allows plugins to maintain state and access system resources such as a device's location while being restricted by Android's process-isolation mechanisms. Experiments with microbenchmarks and case studies with real third-party apps show promising results: plugins are easy to develop and impose acceptable overhead for most resources.

The most promising way to improve the performance of dynamic information-flow tracking (DIFT) for machine code is to only track instructions when they process tainted data. Unfortunately, prior approaches to on-demand DIFT are a poor match for modern mobile platforms that rely heavily on parallelism to provide good interactivity in the face of computationally intensive tasks like image processing. The main shortcoming of these prior efforts is that they cannot support an arbitrary mix of parallel threads due to the limitations of page protections.

Users are increasingly vulnerable to inadvertently leaking sensitive information through cameras. In this paper, we investigate an approach to mitigating the risk of such inadvertent leaks called privacy markers. Privacy markers give users fine-grained control of what visual information an app can access through a device's camera. We present two examples of this approach: PrivateEye, which allows a user to mark regions of a two-dimensional surface as safe to release to an app, and WaveOff, which does the same for three-dimensional objects. We have integrated both systems with Android's camera subsystem. Experiments with our prototype show that a Nexus 5 smartphone can deliver near realtime frame rates while protecting secret information, and a 26-person user study elicited positive feedback on our prototype's speed and ease-of-use.

This paper presents Kahawai1, a system that provides high-quality gaming on mobile devices, such as tablets and smartphones, by offloading a portion of the GPU computation to server-side infrastructure. In contrast with previous thin-client approaches that require a server-side GPU to render the entire content, Kahawai uses collaborative rendering to combine the output of a mobile GPU and a server-side GPU into the displayed output. Compared to a thin client, collaborative rendering requires significantly less network bandwidth between the mobile device and the server to achieve the same visual quality and, unlike a thin client, collaborative rendering supports disconnected operation, allowing a user to play offline - albeit with reduced visual quality.

No abstract available.

Messaging app developers are beginning to take the security and privacy of their users' communication more seriously. Unfortunately, a recent study has shown that the developers of many popular apps incorrectly use cryptography. As a result, they make mistakes that may result in trivially broken encryption schemes. For example, the developers of Snapchat use a constant symmetric encryption key hardcoded into the app and it only takes 12 lines of Ruby to crack the encryption.

The capacity of access links has increased dramatically in recent times, and bottlenecks are moving deeper into the Internet core. When bottlenecks occur in a core (or AS-AS peering) link, it is possible to use additional detour paths to improve the end-to-end throughput between a pair of source and destination nodes. We propose and evaluate a new massively multipath (mPath) source routing algorithm to improve end-to-end throughput for high-volume data transfers. We demonstrate that our algorithm is practical by implementing a system that employs a set of proxies to establish one-hop detour paths between the source and destination nodes. Our algorithm can fully utilize the available access link bandwidth when good proxied paths are available, without sacrificing TCP-friendliness, and achieves throughput comparable to TCP when such paths cannot be found. For 40 percent of our test cases on PlanetLab, mPath achieved significant improvements in throughput. Among these, 50 percent achieved a throughput of more than twice that of TCP.

We show that the performance of downloads in a 3G/HSPA mobile network can be significantly degraded by a concurrent upload that saturates the uplink buffer on the mobile device. In particular, we found in some instances that download speeds can be reduced by over an order of magnitude from 2,000 kbps to 100 kbps. To mitigate this problem, we propose a new algorithm called Receiver-side Flow Control (RSFC) that regulates the uplink buffer on 3G/HSPA data senders. It uses a feedback loop to monitor the available upload capacity and dynamically adjusts the TCP receiver window (rwnd) accordingly. We evaluated RSFC on the 3G/HSPA networks of three different mobile ISPs and show that for one of them, RSFC can improve the download throughput from less than 400 kbps to up to 1,400 kbps. In the presence of a concurrent upload, RSFC can also reduce website load times from more than 2 minutes to less than 1 minute 90% of the time. Our technique is compatible with existing TCP implementations and can easily be deployed at 3G web proxies without requiring any modification to existing mobile devices.