3.3. Windows usage

First of all, you need the knocking utility. The sources are in http://gehennom.org/doc/knock/pknocker.c, and you have to compile them by yourself, because the ports used are hardcoded in the executable. I'm not quite sure what compilers work - personally I use a recent MinGW cross-compiler on Linux. MinGW on a Windows system should definitely work, and perhaps MSVC too.

You also need a SSH client. If you want to do what I did, and put an usable PuTTY (with a private key) on an USB stick, you might want to look at http://gehennom.org/doc/knock/putter.c too. It's an application which creates the relevant registry entries for PuTTY and an SSH session using the key on the stick, and cleans them away when you quit the client. As with pknocker, you need to modify the sources because the session details (and the host public key) are hardcoded in there.