Mashups empower users to easily combine and connect resources from independent Web-based sources and domains. However, these characteristics also introduce new and amplify existing security and privacy problems. This is especially critical in the emerging field of enterprise Mashups. Despite several contributions in the field of Mashup security the issue of protecting exchanged resources against the Mashup-providing Platform has generally been neglected. In this contribution we address the security challenges of server-side Mashup-providing Platforms with the aim of minimizing the required amount of trust. We achieve this by implementing a privacy-enhancing identity management system into the Mashup-providing Platform using Reverse Identity Based Encryption.