In this chapter we look at some existing architectures, protocols and frameworks designed with security in mind. As we shall see, security measures can be implemented at different levels. At the lowest level we discuss IP level security in section 7.1 and Secure RPC in section 7.2. The Secure Socket layer, Secure Shell and Secure HTTP (7.4, 7.3, 7.5) are protocols on somewhat higher levels. Finally, Kerberos, CORBA and SESAME (7.6, 7.7, 7.8) are higher-level security frameworks.