Method and server for providing a mobile key

A method for providing at least one mobile key for cryptographic protection of mobile signaling messages for a home agent via at least one intermediate network, comprising:

• establishing a radio connection between a mobile subscriber terminal and an access network, by an authentication proxy server, in one of the at least one intermediate network, forwarding at least one authentication message, that contains an authenticating subscriber identification, between the access network and a home network of a subscriber, for authentication of the subscriber and, if the authentication by an authentication server of the home network is successful, assigning a group-specific mobile key to the authenticating subscriber identification if the authenticating subscriber identification is already stored in the authentication proxy server;
• receiving, by the home agent in the home network or in one of the at least one intermediate network, a registration request message containing a registering subscriber identification and originating from a registering subscriber terminal;
• transmitting a key request message for a mobile key from the home agent to the authentication proxy server, with the key request message containing the registering subscriber identification;
• providing the group-specific mobile key to the home agent by the authentication proxy server if the registering subscriber identification agrees with a stored subscriber identification in the authentication proxy server;
• and
• deriving a user-specific mobile key by the authentication proxy server, assigning the user-specific mobile key to the authenticating subscriber identification and providing the user-specific mobile key to the home agent, if the authenticating subscriber identification is not stored in the authentication proxy server.