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Practical Dynamic Information Flow Control


Bichhawat,  Abhishek
International Max Planck Research School, MPI for Informatics, Max Planck Society;

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Bichhawat, A. (2018). Practical Dynamic Information Flow Control. PhD Thesis, Universität des Saarlandes, Saarbrücken. doi:10.22028/D291-27244.

Cite as: http://hdl.handle.net/21.11116/0000-0001-9D08-6
Over the years, computer systems and applications have grown significantly complex while handling a plethora of private and sensitive user information. The complexity of these applications is often assisted by a set of (un)intentional bugs with both malicious and non-malicious intent leading to information leaks. Information flow control has been studied extensively as an approach to mitigate such information leaks. The technique works by enforcing the security property of non-interference using a specified set of security policies. A vast majority of existing work in this area is based on static analyses. However, some of the applications, especially on the Web, are developed using dynamic languages like JavaScript that make the static analyses techniques stale and ineffective. As a result, there has been a growing interest in recent years to develop dynamic information flow analysis techniques. In spite of the advances in the field, dynamic information flow analysis has not been at the helm of information flow security in dynamic settings like the Web; the prime reason being that the analysis techniques and the security property related to them (non-interference) either over-approximate or are too restrictive in most cases. Concretely, the analysis techniques gen- erate a lot of false positives, do not allow legitimate release of sensitive information, support only static and rigid security policies or are not general enough to be applied to real-world applications. This thesis focuses on improving the usability of dynamic information flow techniques by presenting mechanisms that can enhance the precision and permissiveness of the analyses. It begins by presenting a sound improvement and enhancement of the permissive-upgrade strategy, a strategy widely used to enforce dynamic information flow control, which improves the strategy’s permissiveness and makes it generic in applicability. The thesis, then, presents a sound and precise control scope analysis for handling complex features like unstructured control flow and exceptions in higher-order languages. Although non-interference is a desired property for enforcing information flow control, there are program instances that require legitimate release of some parts of the secret data to provide the required functionality. Towards this end, this thesis develops a sound approach to bound information leaks dynamically while allowing information release in accordance to a pre-specified budget. The thesis concludes by applying these techniques to an information flow control-enabled Web browser and explores a policy specification mechanism that allows flexible and useful information flow policies to be specified for Web applications.