Today, collaboration is considered a way of improving efficiency and quality of work. This concept is spreading quickly over the technological world, resulting in the organisation of ubiquitous and distributed collaborative environments, which try to provide high-level services based on the interaction among different basic modules. A typical example of this kind of environments are the NGCWEs (Next Generation Collaborative Working Environments). Such working environments try to integrate the experiences of the workers into the system, for which they make use of sensors and low capacity mobile devices. In this paper we take into account all the special features that characterize NGCWEs in order to propose a security model which best fits their requirements. Therefore, we have developed a solution based on symmetric cryptography, and we have introduced the concept of a centralized authorization server, minimizing the load the security solution imposes over the final systems.