The is the usual thing I hear. It is so incredible naive, though. Any service, no matter how locked down and properly configured, still presents an attack sur

The is the usual thing I hear. It is so incredible naive, though. Any service, no matter how locked down and properly configured, still presents an attack surface. SSHD is a program like any other, and it can have bugs. When you use port knocking with a properly configured SSHD, you are much more secure because that attack surface has been removed.