[Dshield] 0wnlng Windows machines

Tony Earnshaw tonni at hetnet.nl
Tue Feb 27 08:25:53 GMT 2007


Stasiniewicz, Adam wrote, on 27. feb 2007 02:44:

> Not quite right.  In a MITM attack a host between the two end points is
> impersonating each end point to the other.  For example, take the following
> diagram:
> 
> 
> Joe User (A)  <->  Evil Guy (B)  <->  SSL Web Server (C)

I never said it wasn't: I've read (and practiced in real time on 
FreeSWAN VPNs) my PKI theory and know well what an MITM attack is.

[...]

> But if a certificate is signed by a trusted CA the above is not possible.
> Take the following model:
> 
> Joe User (A)  <->  Evil Guy (B)  <->  SSL Web Server (C)
> 
> Certificate Authority (D) 
> 
> D has signed C certificate certifying that C really is C.  A's manufacturer
> or administrator has included D public certificate in the list of trusted
> CAs.  Now when A connects to B, B has a certificate that says it is C, but
> since it was not signed by D, A knows that it might be fake (and the user
> will get a warning prompt).

Barlaeus doesn't issue self-signed public certificates; we are our own 
CA authority and we are our own root authority. We ask people to trust 
us as CA authority. There's a great difference between SSH security and 
PKI security.

> It should also be noted; that they way the D identifies C is by DNS name.
> This way the certificate issued to C is only good at identify it as C; it
> cannot be used to identify itself as anyone else.

DNS cache poisoning can and does occur, but this can occur with root-CA 
signed certs too. Our public key is signed and issued (by us, of course) 
to mail.barlaeus.nl and that's its DNS A RR, what's wrong with that?

In any case, the whole question is academic, an MITM attack costs a deal 
of resources to set up - I'm not talking about (`google for "mitm 
"cracking tools"`) - and who'd want to do that for our tiny site? I'd be 
unhappy if my bank were to set up its own CA, but I'm easy with our MTA, 
IMAP server (that last one *is* an SSH - non CA - cert, by the way) and 
https site doing it. The main disadvantage is that there's no CRL 
mechanism and our server could get compromised and the private keys 
nicked, but we go to great lengths both externally and on our internal 
networks to prevent the latter.

Thanks :)

--Tonni

-- 
Tony Earnshaw
Email: tonni at hetnet dot nl


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