The appliance uses a certificate for authentication over SSL. The certificate contains a public key, and the appliance maintains the corresponding private key, which is uniquely tied to the public key.
A self-signed certificate indicates that a host vouches for itself, which, in some cases, might be adequate. By default, browsers do not trust self-signed certificates and display a warning.
A more secure alternative is a certificate issued by a third-party certificate authority. For information on these certificates, see Create a certificate signing request.