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

[Pete Herzog <lists () isecom org>]

Hi,

> 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.

Sincerely,
-pete.

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