The SSM model is appeared in order to overcome the problems of deployment of IP multicast. However, a real commercial deployment of SSM have to offer some security services. Our work proposes an architecture, called S-SSM, for securing the SSM model. S-SSM defines two mechanisms for access control and content protection. The first one is carried out through subscriber authentication and access permission. As for the second, it is realized through the management of a unique key, called the channel key, k_ch, shared among the sender and subscribers. We have implemented a prototype of S-SSM in order to prove the feasability and evaluate the performance of our design.