Google's Android platform includes a permission model that protects access to sensitive capabilities, such as Internet access, GPS use, and telephony. While permissions provide an important level of security, for many applications they allow broader access than actually required. In this paper, we introduce a novel framework that addresses this issue by adding finer-grained permissions to Android. Underlying our framework is a taxonomy of four major groups of Android permissions, each of which admits some common strategies for deriving sub-permissions. We used these strategies to investigate fine-grained versions of five of the most common Android permissions, including access to the Internet, user contacts, and system settings. We then developed a suite of tools that allow these fine-grained permissions to be inferred on existing apps; to be enforced by developers on their own apps; and to be retrofitted by users on existing apps. We evaluated our tools on a set of top apps from Google Play, and found that fine-grained permissions are applicable to a wide variety of apps and that they can be retrofitted to increase security of existing apps without affecting functionality.

Test-driven methodologies encourage testing early and often. Mock objects support this approach by allowing a component to be tested before all depended-upon components are available. Today mock objects typically reflect little to none of an object's intended functionality, which makes it difficult and error-prone for developers to test rich properties of their code. This paper presents declarative mocking, which enables the creation of expressive and reliable mock objects with relatively little effort. In our approach, developers write method specifications in a high-level logical language for the API being mocked, and a constraint solver dynamically executes these specifications when the methods are invoked. In addition to mocking functionality, this approach seamlessly allows data and other aspects of the environment to be easily mocked. We have implemented the approach as an extension to an existing tool for executable specifications in Java called PBnJ. We have performed an exploratory study of declarative mocking on several existing Java applications, in order to understand the power of the approach and to categorize its potential benefits and limitations. We also performed an experiment to port the unit tests of several open-source applications from a widely used mocking library to PBnJ. We found that more than half of these unit tests can be enhanced, in terms of the strength of properties and coverage, by exploiting executable specifications, with relatively little additional developer effort.