Re: an anternative to port-knoking using the OpenBSD pf only


fingerprints) are not encrypted so their content can be easly sniffed

Easily perhaps from many internal networks. But it's much more difficult for an attacker to sniff it without access to
either the client's network and the server's network. It's
not impossible but difficult enough to warrant OpenBSD pf attention as a type of protection.

out. Port knocking increases sealthness (so it can probably be considered a security measure) but cannot be used to make a system safe.

Stealthiness is privacy. Privacy is a loss control and does make an operation safer. The efficacy of the privacy loss control, as there can be degrees like as in encryption, however does take issue. So whether or not this type of port knocking is good enough is really the question and not whether it protects at all because it does. Even obfuscation is protection albeit not a good one but it will minimize some types of attacks. This is in many ways like Anti Virus or the IDS that relies on black lists. They narrow the kind of data which enters a host or network by authorizing that which it does not know to reject. Would you consider either of those technologies to not be a form of protection? At least port knocking is white list :)

I've noted that many people misunderstand the port-knocking's meaning, it's not a security layer and doesn't prevent security holes, it can only make your system quite harder to hack.

But it is a security layer because it makes a system harder to hack. How is that not a security layer?

Anyway the use of port-knocking to make a system safer can be a bad solution, because it's just like wrapping a vault with cellophane. You can use it to hide a computer in internet, or to keep your logfiles clean as you can use cellophane to protect iron against rain.

Well then it does protect the vault from rain, right? It's still protecting. Not every loss control is going to be of the bunker type. Again, look at any black list technology and you'll see the same thing. I have done years of narrow studies on this and I can prove that simply moving a service to a different port will provide an every day layer of protection. But not every attack. Then again, it's not supposed to. It's only supposed to fend off the automated which is already a lot. This is why internet crime is so much easier than say, cat burglary because of automation they can find many more potential targets.

Gimeshell, it's not right to consider tcp options size unlimited, and I think the real port-knoking is harder to brutefoce. Authentication through os fingerprints cannot use all tcp options (p0f doesn't analyze them all) and, anyway, it must fit tcp options structure and respect the protocol rules.

This is true but it doesn't dismiss the concept as a layer of protection. It's also not an industrial solution and it doesn't scale well at all. But for some purposes, it's possible to implement and maintain inexpensively.


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