Re: [dane] Behavior in the face of no answer?

[Andrew Sullivan <[e-mail]>]

On Thu, May 03, 2012 at 03:44:57PM -0700, Eric Rescorla wrote:
> 
> Well, I absolutely have a problem.... I'm under active attack :)
> 
> However, if you choose option (a) and hard fail, then all the attacker
> can do is create a failure. However, if you choose option (b) then
> the attacker is able to cause you to connect to his server even
> though the domain operator is trying to serve you a DNSSEC-signed
> DANE record which tells you not to accept that cert (if you
> could only get that record).

No, I think I still don't understand.  Under (b), how can the attacker
get you to connect to "his server"?  The attacker can get you to
connect to some server and foil your attempt to use the TLSA-provided
credential, but how do you go to the wrong server?

You can't get the A or AAAA record if the attacker is fiddling with
the DNS, because that RRset will fail DNSSEC validation in the first
place.  Remember, we're already depending on DNSSEC.  If you _can_ get
the right address, then the problem is that you use the wrong
certificate (i.e. you fall back to the X.509 chain)?  Unless the X.509
chain is somehow subverted, though -- but how is that any more of a
danger than "compromised key in TLSA"?

A

-- 
Andrew Sullivan
[e-mail]