Security and mobility overlay architecture (SAMOA) includes security management and secure transport functions for fixed or mobile security subscriber units (SSUs). SSUs within SAMOA are authenticated, authorized, and provided with shared session keys by the security management function. The keys allow each SSU to communicate with the secure transport network, which provides secure connections to other SSUs. Because shared-key, rather than public-key session keys are preferably used, the problems associated with public-key certificate authorities and hierarchies are avoided. The security management function and the secure transport network can be layered efficiently on top of existing Internet protocol (IP) networks and are thus applicable to a wide range of systems that support IP, including 3G wireless, wireless LANs (e.g., 802.11x), wired LANs, and dial-up networks.