Master of Science in Computing and Internet Systems

King's College London (UK)

September 2011 - September 2012


Thesis

A Secure Web-server

The research project of this thesis comprises the design, implementation and test of a secure web-server. We mainly focused on the implementation of the so called Privilege Separation principles, which state that a program can be split up into several parts with different privilege levels. By applying these principles to a web-server, we wanted to create a system, which behaves in a solid way on attacks of malicious users.

Our server architecture contains three different types of processes, which run with different privileges. In order to obtain maximum security, clients interact just with unprivileged processes, that cannot harm the system. However a privileged process is also needed for performing specific tasks. This process stays in background, isolated from being directly accessed, and cannot therefore be easily taken over by an attacker.

The system was developed using the Python programming language and represents a fully functional web-server, that is able to serve static and dynamic websites. A major challenge during the project has been represented by the asynchronous Interprocess Communication. Privilege Separation split up the program among several processes. Realising the communication between these processes required to take into consideration various issues related to concurrency, efficiency and functionality.

The ultimate goal of this thesis project was to understand, whether Privilege Separation can make a web-server more secure. We compared our system, with the world's most used web-server, Apache. The evaluation showed, that Privilege Separation influences the security of a web-server in a positive way, however affects its performance negatively.

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