Sven Bugiel

Practical and lightweight domain isolation on Android

In this paper, we introduce a security framework for practical and lightweight domain isolation on Android to mitigate unauthorized data access and communication among applications of different trust levels (e.g., private and corporate). We present the design and implementation of our framework, TrustDroid, which in contrast to existing solutions enables isolation at different layers of the Android software stack: (1) at the middleware layer to prevent inter-domain application communication and data access, (2) at the kernel layer to enforce mandatory access control on the file system and on Inter-Process Communication (IPC) channels, and (3) at the network layer to mediate network traffic. For instance, (3) allows network data to be only read by a particular domain, or enables basic context-based policies such as preventing Internet access by untrusted applications while an employee is connected to the companys network. Our approach accurately addresses the demands of the business world, namely to isolate data and applications of different trust levels in a practical and lightweight way. Moreover, our solution is the first leveraging mandatory access control with TOMOYO Linux on a real Android device (Nexus One). Our evaluation demonstrates that TrustDroid only adds a negligible overhead, and in contrast to contemporary full virtualization, only minimally affects the batterys life-time.

Twin clouds: secure cloud computing with low latency

Cloud computing promises a cost effective enabling technology to outsource storage and massively parallel computations. However, existing approaches for provably secure outsourcing of data and arbitrary computations are either based on tamper-proof hardware or fully homomorphic encryption. The former approaches are not scaleable, while the latter ones are currently not efficient enough to be used in practice. We propose an architecture and protocols that accumulate slow secure computations over time and provide the possibility to query them in parallel on demand by leveraging the benefits of cloud computing. In our approach, the user communicates with a resource-constrained Trusted Cloud (either a private cloud or built from multiple secure hardware modules) which encrypts algorithms and data to be stored and later on queried in the powerful but untrusted Commodity Cloud. We split our protocols such that the Trusted Cloud performs security-critical precomputations in the setup phase, while the Commodity Cloud computes the time-critical query in parallel under encryption in the query phase.

Android security framework: extensible multi-layered access control on Android

We introduce the Android Security Framework (ASF), a generic, extensible security framework for Android that enables the development and integration of a wide spectrum of security models in form of code-based security modules. The design of ASF reflects lessons learned from the literature on established security frameworks (such as Linux Security Modules or the BSD MAC Framework) and intertwines them with the particular requirements and challenges from the design of Androids software stack. ASF provides a novel security API that supports authors of Android security extensions in developing their modules. This overcomes the current unsatisfactory situation to provide security solutions as separate patches to the Android software stack or to embed them into Androids mainline codebase. This system security extensibility is of particular benefit for enterprise or government solutions that require deployment of advanced security models, not supported by vanilla Android. We present a prototypical implementation of ASF and demonstrate its effectiveness and efficiency by modularizing different security models from related work, such as dynamic permissions, inlined reference monitoring, and type enforcement.

Scippa: system-centric IPC provenance on Android

Googles Android OS provides a lightweight IPC mechanism called Binder, which enables the development of feature-rich apps that seamlessly integrate services and data of other apps. Whenever apps can act both as service consumers and service providers, it is inevitable that the IPC mechanism provides message receivers with message provenance information to establish trust. However, the Android OS currently fails in providing sufficient provenance information, which has led to a number of attacks. We present an extension to the Android IPC mechanism, called Scippa, that establishes IPC call-chains across application processes. Scippa provides provenance information required to effectively prevent recent attacks such as confused deputy attacks. Our solution constitutes a system-centric approach that extends the Binder kernel module and Androids message handlers. Scippa integrates seamlessly into the system architecture and our evaluation shows a performance overhead of only 2.23% on Android OS v4.2.2.

Trust in a small package: minimized MRTM software implementation for mobile secure environments

In this paper we present a software-based implementation of a Mobile Remote Owner Trusted Module, using security extensions of contemporary System-On-Chip architectures. An explicit challenge are the constrained resources of such on-chip mechanisms. We expose a software architecture that minimizes the code and data size of the MRTM, applying some novel approaches proposed in recent research. Additionally, we explore alternatives within the specification to further optimize the size of MTMs. We present an analysis of specific new security issues induced by the architecture. Performance figures for an on-the-market mobile handset are provided. The results clearly indicate that a software-based MRTM is feasible on modern embedded hardware with legacy security environments.

TruWalletM: secure web authentication on mobile platforms

Mobile phones are increasingly used as general purpose computing devices with permanent Internet connection. This imposes several threats as the phone operating system (OS) is typically derived from desktop counterparts and, hence, inherits the same or similar security shortcomings. In particular, the protection of login credentials when accessing web services becomes crucial under phishing and malware attacks. On the other hand many modern mobile phones provide hardware-supported security mechanisms currently unused by most phone OSs. In this paper, we show how to use these mechanisms, in particular trusted execution environments, to protect the users login credentials. We present the design and implementation proposal (based on Nokia N900 mobile platform) of TruWalletM, a wallet-like password manager and authentication agent towards the protection of login credentials on a mobile phone without the need to trust the whole OS software. We preserve compatibility to existing standard web authentication mechanisms.

SoK: Lessons Learned from Android Security Research for Appified Software Platforms

Android security and privacy research has boomed in recent years, far outstripping investigations of other appified platforms. However, despite this attention, research efforts are fragmented and lack any coherent evaluation framework. We present a systematization of Android security and privacy research with a focus on the appification of software systems. To put Android security and privacy research into context, we compare the concept of appification with conventional operating system and software ecosystems. While appification has improved some issues (e.g., market access and usability), it has also introduced a whole range of new problems and aggravated some problems of the old ecosystems (e.g., coarse and unclear policy, poor software development practices). Some of our key findings are that contemporary research frequently stays on the beaten path instead of following unconventional and often promising new routes. Many security and privacy proposals focus entirely on the Android OS and do not take advantage of the unique features and actors of an appified ecosystem, which could be used to roll out new security mechanisms less disruptively. Our work highlights areas that have received the larger shares of attention, which attacker models were addressed, who is the target, and who has the capabilities and incentives to implement the countermeasures. We conclude with lessons learned from comparing the appified with the old world, shedding light on missed opportunities and proposing directions for future research.

Android security framework : enabling generic and extensible access control on Android

We introduce the Android Security Framework (ASF), a generic, extensible security framework for Android that enables the development and integration of a wide spectrum of security models in form of code-based security modules. The design of ASF reflects lessons learned from the literature on established security frameworks (such as Linux Security Modules or the BSD MAC Framework) and intertwines them with the particular requirements and challenges from the design of Androids software stack. ASF provides a novel security API that supports authors of Android security extensions in developing their modules. This overcomes the current unsatisfactory situation to provide security solutions as separate patches to the Android software stack or to embed them into Androids mainline codebase. As a result, ASF provides different practical benefits such as a higher degree of acceptance, adaptation, and maintenance of security solutions than previously possible on Android. We present a prototypical implementation of ASF and demonstrate its effectiveness and efficiency by modularizing different security models from related work, such as context-aware access control, inlined reference monitoring, and type enforcement.

Implementing an application-specific credential platform using late-launched mobile trusted module

Contemporary trusted execution environments provide a good foundation for implementing secure user credentials, but these are not properly bound to the application instances that implement their use. This paper introduces a framework for application-specific credentials and provides a prototype implementation using TCG MTM and DRTM technologies. Measurements and a security analysis is presented for the realised architecture.

ARTist: The Android Runtime Instrumentation and Security Toolkit

With the introduction of Android 5 Lollipop, the Android Runtime (ART) superseded the Dalvik Virtual Machine (DVM) by introducing ahead-of-time compilation and native execution of applications, effectively deprecating seminal works such as TaintDroid that hitherto depend on the DVM. In this paper, we discuss alternatives to overcome those restrictions and highlight advantages for the security community that can be derived from ARTs novel on-device compiler dex2oat and its accompanying runtime components. To this end, we introduce ARTist, a compiler-based application instrumentation solution for Android that does not depend on operating system modifications and solely operates on the application layer. Since dex2oat is yet uncharted, our approach required first and foremost a thorough study of the compiler suites internals and in particular of the new default compiler backend called Optimizing. We document the results of this study in this paper to facilitate independent research on this topic and exemplify the viability of ARTist by realizing two use cases. In particular, we conduct a case study on whether taint tracking can be re-instantiated using a compiler-based app instrumentation framework. Overall, our results provide compelling arguments for the community to choose compiler-based approaches over alternative bytecode or binary rewriting approaches for security solutions on Android.