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Private Computing and Mobile Code Systems

This thesis' objective is to provide privacy to mobile code. A practical example of mobile code is a mobile software agent that performs a task on behalf of its user. The agent travels over the network and is executed at different locations of which beforehand it is not known whether or not these can be trusted. Because a mobile software agent performs actions on behalf of its user, agent must be protected in order to provide privacy to the user. For example, a software agent must purchase a flight ticket. Other parties like airlines are then not entitled to know the agent's strategy when the agent will purchase the ticket. In this thesis, several solutions are provided to this problem, and to obtain more in depth knowledge on protecting privacy in mobile code a theoretical analysis was performed. Essential in this problem is that the execution environment cannot be trusted. It is curious in the content of the mobile code, although it does not change the content. Two approaches are covered in this thesis. First, a practical approach is given that presents several solutions to various aspects of the mobile code privacy problem. These solutions provide a level of privacy protection, however, it does not provide knowledge on what level of privacy can be provided. To answer this question a theoretical analysis is made to derive limits of the maximum privacy level that can be achieved