The world-wide computing network has recently seen a proliferation of web-service and other distributed system platforms. In order to couple services in such an environment it will be necessary to develop techniques to support negotiation between parties that do not openly share information. Previous incremental trust negotiation approaches cater for limited credential disclosure through features of policy design. In contrast, this paper presents an algorithm which supports limited credential disclosure by performing incremental negotiations in a hashed target-space. We demonstrate our method by discussing its integration into a parameterised role-based access control system.