US Patent 9258117 Mutual authentication with symmetric secrets and signatures

A client and server negotiate a secure communication channel using a pre-shared key where the server, at the time the negotiation initiates, lacks access to the pre-shared key. The server obtains the pre-shared key from another server that shares a secret with the client. A digital signature or other authentication information generated by the client may be used to enable the other server to determine whether to provide the pre-shared key.