Achieving privacy preservation in a data-sharing computing environment is becoming a challenging problem. Some organisations may have published privacy policies, which promise privacy protection practices on data collection, use and disclosure, but these practices may not be implemented. To maintain consistency between the privacy policy and the practices, privacy protection requirements in privacy policy should be formally specified. In specifying privacy policy, we use purpose as the basis of access control. In this paper, we extend our previous work to specify purpose management. Purpose can be divided into two categories: intended purpose and access purpose. Privacy policy is to ensure that data can only be used for its intended purpose, and the access purpose should be compliant with the data's intended purpose. We specify entities in the purpose-based access control model. Using the technique of VDM, we then specify the invariants corresponding to the privacy requirements in privacy policy, and then specify the operations in the model and investigate their proof obligations.

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Mobile agent systems employ a number of security features to address the various threats. Despite these mechanisms they do have to make certain assumptions for the trustfulness of other entities within the agent system. This paper intends to present the ways in which mobile agent trust models address specific threat scenarios, by comparing the behaviour of four major mobile agent platforms. The conclusions drawn are then used to point out deficiencies of current technology and highlight issues that need to be addressed by future research.