Recent widespread deployment of different types of sensors and detectors has opened the door to a new way of understanding collaborative applications. The use of such devices allows information to be collected, used and disclosed on a massive scale and under very different conditions from which we are currently familiar with. Despite the huge potential of these collaborative environments, privacy is one of their most criticized aspects and probably the greatest barrier to their long-term success. To address this problem, we present a privacy-enhancing security model specifically tailored to the characteristics of ubiquitous and heterogeneous environments consisting of low capacity devices. This security model is based on the Kerberos symmetric key protocol which has been modified and extended to avoid using timestamps and to accomplish the authorization process. Finally, we present a validation of our proposal using an automated tool and we show a real world deployment use case.