In computer networking, port knocking is a method of externally opening ports on a firewall by generating a connection attempt on a set of prespecified closed ports. Once a correct sequence of connection attempts is received, the firewall rules are dynamically modified to allow the host which sent the connection attempts to connect over the specific port(s). A variant called single packet authorization exists, where only a single "knock" is needed, consisting of an encrypted packet.
The primary purpose of port knocking is to prevent an attacker from scanning a system for potentially exploitable services by doing a port scan because unless the attacker sends the correct knock sequence, the protected ports will appear closed.
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Durante una discussione, ho trovato la seguente domanda: Considerando un amministratore (come nell'amministratore del server) o persino un utente malintenzionato (come nel cattivo che cerca di ottenere l'accesso alla macchina) un metodo di bussare alla porta può essere considerato una forma di autenticazione verso quel server?