A method is provided for implementing a security association for a terminal being attached to an access network. The method includes the following steps, carried out by an authentication server of the access network, after receiving a request coming from the terminal for attachment to the network: receiving a first message containing at least one security association parameter from a bootstrapping server function; authenticating the terminal by using at least one first authentication parameter provided by a home subscriber server of the terminal; and sending a security association message containing the at least one security association parameter to the authenticated terminal.