Use port knocking
So-called "Simple" client classes (TElSimpleSSLClient, TElSimpleSSHClient, TElSimpleSFTPClient, TElSimpleFTPSClient, TElHTTPSClient, TElSMTPClient etc.) that offer implementation of popular network protocols have a powerful built-in TCP socket that support s port knocking.
Port knocking is a mechanism using which the client can tell the server to open certain port for the client to connect to that port. Knocking is done by consequently sending packets to certain TCP or UDP ports using certain predefined scheme (the order of being packets sent).
SecureBlackbox implements the simple port knocking scheme (both TCP and UDP requests are supported) in all of its socket-based components.
To use port knocking you should assign as instance of TElPortKnock class to the PortKnock property of the corresponding Simple client class.