A method, a mobile node (MN) and a correspondent node (CN) exchanging a Secret Authentication Key (SKbm) within an IPv6 network. The MN has a pair of keys comprising a private key and a public key and a HoA. Upon displacement of the MN from a home portion to a visited portion of the IPv6 network, a CoA is set. Thereafter, an establishment message is sent from the MN to the CN through a Home Agent associated to the MN. Upon reception of the establishment message, the CN tests the HoA and the CoA and therefor sends a first portion and a second portion of a secret data. The MN thereafter sends the secret data back to the CN within a signed message. In response thereto, the CN sends an acknowledgement message to the MN comprising the SKbm encrypted using the public key of the MN.