Attack surface almost entirely goes away if you just require a good port knock first! I do that with my protection SSH servers and it works just fine. Also prevents anyone from knowing there even is an SSH server there. Or any server if it doesn't respond to pings either, and only uses reverse tunnels to accept public connections
Dunno, in combination with having an up to date system following best practices, port knocking is probably going to save you when bots start scanning the internet with the next SSH 0day. Any amount of friction will cause the bots to move to the next IP address.
My knock for SSH was 20 ports within 2 seconds. knockd resets the sequence if you hit any of its ports out of order. I generated the sequence with a CSPRNG.
I mean, it suffers from some of the same issues with knocks, like being replayable. Wonder if anyone's come up with a TOTP-like thing for port knocks, where the code changes every little bit...
That’s cute. Have Claude do it. There is already an echo system of TOPT QR to communicate it, so you would just need to convert your six digit code to two or more hits on the 16bit port range.
I’m not even sure you need more than two. One seems bad because that’s just a lucky port scanner one time.
Yes something like that has been done, the solution uses asymmetric cryptography instead of symmetric and it protects the entire communication stream instead of just opening the gates - it's called Wireguard.
I jest, but you're describing authentication protocol which uses the UDP destination port field to carry each character of the "one time password" in a roundabout way. You could simply send 1 packet containing the password to the daemon.
LOL'd at Wireguard, but I really miss Plan 9-style networking, where you can basically just scope VPNs to a subprocess rather than having to use some system wide network filter with split tunneling or whatever. Wireguard has huge usability issues due to that.
Reading the fwknop README is such a breath of fresh air, thank you for that treat. I hate AI-generated documentation so much.
You're sending your knock over the public network in the clear. It's observable by anything in the path. And then you're not the only one that can find the keyhole.
Entirely true, it's not true security, same as changing the ssh port. So, relying on it for any security is not useful but it's a good deterrent from automated scans that are not targeted towards you. Defense in depth means not necessarily discarding flawed defenses if they are in addition to proper defense.
