  The emergence of network technologies and the appearance of new varied
applications in terms of services and resources, has created new security
problems for which existing solutions and mechanisms are inadequate, especially
problems of identification and authentication. In a highly distributed and
pervasive system, a uniform and centralized security management is not an
option. It then becomes necessary to give more autonomy to security systems by
providing them with mechanisms that allows a dynamic and flexible cooperation
and collaboration between the actors in the system.
