In one embodiment, a method of the invention has the steps of: (A) establishing an access-layer security association (SA) between a mobile node (MN) and an authentication authorization accounting (AAA) server; (B) deriving a secondary key from an extended master session key (EMSK) corresponding to the access-layer SA; (C) providing the secondary key to a home agent; and (D) based on the secondary key, establishing an SA corresponding to an Open System Interconnection (OSI) layer higher than the access layer for securing communications between the home agent and a selected network node. In various embodiments, the selected network node can be (i) the MN, (ii) a proxy node configured on behalf of the MN, or (iii) a proxy node configured on behalf of the home agent.