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

[poplix <poplix () papuasia org>]

If an attacker has targetted your system, port-knocking and this  
alternative are totally useless. Knokcing sequences (and os  
fingerprints) are not encrypted so their content  can be easly  
sniffed out. Port knocking increases sealthness (so it can probably  
be considered a security measure) but cannot be used to make a system  
safe.
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.
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.


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.

poplix


On 17 Feb 2006, at 9:52 AM, gimeshell () web de wrote:

> On Mon, 23 Jan 2006 22:44:52 +0100
> poplix <poplix () papuasia org> wrote:
> >    OUT (tcp.flags='syn')
> >     set(
> >      tcp.win='8192',ip.ttl='128',ip.flags.df='0',
> >      tcp.options='mss=3884+noop+wss=0+noop+noop+ts=TS'
> >     );
> >
> >    This rule tells tripp to rewrite all outgoing tcp packets with
> > the SYN
> >    flag set only allowing my first handshake packet to match "poplix"
> >    fingerprint.
>
> Does an attacker who wants to attack a server include aspect that
> this maybe a system utilizing port knocking in this way?
> Perhaps if he has focused at this system?
>
> Am i right to say, your invented os fingerprint is random and unique
> and because of unlimited IP option field's length there's no
> chance left for attacker to brute force ports with different option
> field values et cetera to get correct option field + window size +  
> ttl +
> flag?
>
> regards
>
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