Numerous vulnerabilities threat the security of Mobile IP (MIP) networks. A variety of methods have been proposed to protect the MIP networks from the attacks. However, most of these methods are heavy and require significant time and resources. MIP is an essential element within the wireless mobile communication network that provide a fixed IP address. Among the changes from the existing standard IP network to the MIP network, security is a most essential one. Handover delay has been increased because of the complicated authentication and registration process. Because the essential goals of MIP are to provide seamless connection and real-time services, the security vulnerability became the biggest problem for the real deployment. To solve this problem, this paper proposes a new lightweight authentication mechanism for the authentication, authorization, and accounting (AAA) infrastructure of MIP networks. In the original AAA authentication mechanism, mobile node (MN) must wait for a nonce from an AAA server in order to generate the session key, which be used for the security associations between MN and home agent and between MN and foreign agent. This paper introduces a new mechanism, which enables the unauthenticated MN to initiate a key generation process and create a secret key in advance. This mechanism facilitates key distribution by reducing cryptographic operations (76.68% improvement) and handover time (14.15% improvement). Copyright (C) 2016 John Wiley & Sons, Ltd.