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

[Andrew Sullivan <[e-mail]>]

On Thu, May 03, 2012 at 07:14:33PM -0700, Nicholas Weaver wrote:
> 
> An IN-path adversary doesn't need to manipulate the A or AAAA records to get you to connect to their server.
> 

Ah, ok, so we're talking about someone who can both intercept and
redirect your connection to a target address and block DNS responses
from getting to you but who cannot re-engineer DNS responses for you
(obviously, because it'd fail at the root trust anchor).  Ok, now I
get it.

> Since the adversaries of concern are likely to be in-path, not just
> on-path, this is a serious concern and DANE when it can't get the
> record it MUST hard fail lest it be useless in the face on an
> in-path attacker, which is critical since the goal of all this
> cryptomagic is to deal with in-path attackers.

Surely this is a matter of local policy?  That is, it's probably a
pretty good idea if it fails, and if you know what you are doing you
probably want to say "fail if I can't get a TLSA response at all"; but
during deployment and roll-out (as someone already argued up-thread)
this is simply an unrealistic requirement: people are going to be
behind broken devices for some years now, and a protocol-required hard
fail requirement will either be ignored or else will delay deployment
until we complete upgrading the Internet.  I suggest while we are
waiting for that, we might want to work on DNS2 and TLS2.  If that's
not enough, I'm sure we can find some more windmills.  Alternatively,
we could just let people fall back to the infrastructure we have.

Note that there remain _plenty_ of DNS servers deployed in the wild
which, if you ask them for an RRTYPE they don't know about, spit up
with NOTIMP, SERVFAIL, and all manner of other crappy nonsense.  (We
were just having a bunfight about that over in SPFBIS a month or two
ago.)  Turning off TLS for anyone whose client knows about TLSA, but
who is trying to go to a service offered by someone employing a broken
DNS server like this, is not reasonable.

Speaking as an operator, I can tell you that if the protocol says
"hard fail if I don't get a TLSA answer", I will tell all my customers
not to use TLSA; the alternative is to make my customers mad at me the
day someone's connection from some crappy hotel network fails.  I'd
hate to be put in that position.

A

-- 
Andrew Sullivan
[e-mail]