Hybrid approaches for enforcing security policies.

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In our highly connected and highly computerized world, security issues are of major importance. ***Trusted systems need to communicate with untrustworthy parties exposing the users to a risk of information leakage or data corruption. It is urgent to find effective solutions to protect users. Despite major research efforts that have been devised, there still are many challenging problems to be explored.***My broad research aim is to contribute to the design of provably sound techniques, methods and enforcement mechanisms that enforce security policies at the level of applications. ***Mechanisms such as access control, encryption, firewalls, digital signatures, and antivirus scanning are either too restrictive, causing loss of flexibility, or unable to protect from newly introduced threats or malicious attacks. One of the underlying reasons is that they do not address the fundamental problem, which is tracking information flow in a fine-grained application-specific way. To do this one needs to analyze the code of an application; this research trend is known as "language-based security". In this research program, I will address information flow enforcement mechanisms that prevent information from flowing from a higher security level to a lower one or in a dual way to prevent lower security level data from corrupting higher ones. The main idea is to inspect the code of an application and control its execution in order to apply the policy. ***I will adopt the following objectives and methodological lines. ******1. Introducing the least overhead possible while reducing false positives. A hybrid approach combining static and dynamic analysis in an effective way is to be adopted. ***2. Dealing with declassification. Declassification means an intentional leak from higher security levels to lower ones. ***Information flow policy is very restrictive; real-world applications release information as part of their intended function. For instance, login procedures, communication of encrypted data, or voting systems do not comply with information-flow policy. Release of some information must be allowed but controlled to prevent non-intended leaks. ******3. Designing mechanisms that target more expressive languages such as concurrent languages. More challenging issues may appear such as timing channels, which cause leaks due to attackers' capacity to observe time. Extensive data-flow analysis and semantic models suitable to concurrency will be adopted. ***4. Quantifying the amount of leakage in a probabilistic framework. The aim is to relax non-interference and tolerate some quantified leaks. ***5. Leveraging all these techniques to a real world language. *********The results will provide practical and theoretical foundations for the development of effective and robust mechanisms to preserve the confidentiality and the integrity of their data. *** **