Cars are getting rapidly connected with their environment allowing all kind of mobility services based on the data from various sensors in the car. Data privacy is in many cases only ensured by legislation, i. e., the European General Data Protection Regulation (GDPR), but not technically enforced. Therefore, we present a system model for enforcing purpose limitation based on data tagging and attribute-based encryption. By encrypting sensitive data in a way only services for a certain purpose can decrypt the data, we ensure access control based on the purpose of a service. In this paper, we present and discuss our system model with the aim to improve technical enforcement of GDPR principles. CCS CONCEPTS • Security and privacy → Human and societal aspects of security and privacy; Privacy protections; Usability in security and privacy; • Computer systems organization → Special purpose systems.