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I just hope that anyone doing that only does it with private networks. I still remember that painful time I had to debut the fact that someone was blocking the heartbeat TLS extension by simply dropping traffic and I had a product that most of the time sent that extension by default ("everything else can connect, so it's clearly your fault that you cannot"). I also hope that said network actually patched Heartbleed, but I sincerely wonder about that.

While not quite to the same level of obfuscation, your suggestion reminded me of this project: http://www.cipherdyne.org/fwknop/ Its essentially port knocking with a single encrypted packet.

Haven't tried it (yet) myself but sounds interesting.

See fwknop and the history of port knocking.

Some information on this is located in the fwknop tutorial:

http://www.cipherdyne.org/fwknop/docs/fwknop-tutorial.html