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Grabowski, Robert (2012): Information flow analysis for mobile code in dynamic security environments. Dissertation, LMU München: Faculty of Mathematics, Computer Science and Statistics
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Abstract

With the growing amount of data handled by Internet-enabled mobile devices, the task of preventing software from leaking confidential information is becoming increasingly important. At the same time, mobile applications are typically executed on different devices whose users have varying requirements for the privacy of their data. Users should be able to define their personal information security settings, and they should get a reliable assurance that the installed software respects these settings. Language-based information flow security focuses on the analysis of programs to determine information flows among accessed data resources of different security levels, and to verify and formally certify that these flows follow a given policy. In the mobile code scenario, however, both the dynamic aspect of the security environment and the fact that mobile software is distributed as bytecode pose a challenge for existing static analysis approaches. This thesis presents a language-based mechanism to certify information flow security in the presence of dynamic environments. An object-oriented high-level language as well as a bytecode language are equipped with facilities to inspect user-defined information flow security settings at runtime. This way, the software developer can create privacy-aware programs that can adapt their behaviour to arbitrary security environments, a property that is formalized as "universal noninterference". This property is statically verified by an information flow type system that uses restrictive forms of dependent types to judge abstractly on the concrete security policy that is effective at runtime. To verify compiled bytecode programs, a low-level version of the type system is presented that works on an intermediate code representation in which the original program structure is partially restored. Rigorous soundness proofs and a type-preserving compilation enable the generation of certified bytecode programs in the style of proof-carrying code. To show the practical feasibility of the approach, the system is implemented and demonstrated on a concrete application scenario, where personal data are sent from a mobile device to a server on the Internet.