This document describes a handover authentication protocol based on the AAA server in FMIPv6. The proposed scheme employs the Diffie- Hellman (DH) algorithm to enhance security aspects, and modifies the DH key exchange to reduce computational cost at the Mobile Node (MN) by delegating exponential operation to the AAA server. The MN and Access Router (AR) establish the handover key HK through the AAA server. The main advantage of this document is more secure and suitable to a light-weight mobile terminal.