Traditionally, QoS and security issues have been treated separately. Clearly, this cannot be the best choice to make: security mechanisms may severely affect network or system performances in a context where the resources are limited. On the other hand, the applied security level for each application strongly depends on available network or system resources. Then, security and QoS have mutual dependent performances, and a trade-off between environment performances and security policies seems to be useful and quite relevant for the studied context.