The pre-shared key method of authentication enables a remote host to authenticate itself by providing a secret key, which is known to both hosts. This key is pre-configured by the administrator, and is used along with the Diffie-Hellman shared secret to derive cryptographic keys used to protect and authenticate data that flows during the phase 1 negotiation. The pre-shared key is a shared secret between the two IKE peers, and any host that does not know the shared key cannot enter into negotiation. IKE maintains a list of all the remote hosts that are authorized to negotiate. This list contains the identity of the remote host and the pre-shared key known to that host.