Modeling and expressing purpose validation policy for privacy-aware usage control in distributed environment

Privacy-aware usage control is a control of the usage of private data with the aim to protect data owner privacy. In privacy-aware system, the purpose of data usage is strictly controlled to ensure that data owner privacy is properly protected and data would never be used beyond what it is authorized for. To fulfill that level of protection, it requires the strong enforcement of usage policy, in particular, the enforcement of the purpose of data usage. However, there are many difficulties in purpose enforcement. One of which is to validate the purpose of an agent when it requests to perform an action, particularly in distributed environments where the processing of data is carried out on client side application and direct control of it is limited. Generally, validating "a particular purpose" may require different mechanisms and can happen at different points in time during the lifecycle of data usage. Hence, there is a need to express "how purpose should be validated" by indicating which validation mechanisms should be used and when the validation should take place so that the remote system can act as instructed. In this paper, we discuss the design issue of purpose validation policy expression based on our proposed validation structure: pre-, ongoing-, and post-validation. Furthermore, we discuss how the existing languages such as EPAL, XACML, and ODRL can directly be used or extended to support our proposed purpose validation policy model.