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

[Andrew Sullivan <[e-mail]>]

On Thu, May 03, 2012 at 08:18:41PM -0700, Eric Rescorla wrote:
> 
> While I understand that these operational constraints, I'm having
> trouble understanding what security benefit DANE offers if one behaves
> as you suggest, since it seems the attacker can simply force you to
> ignore any records that DANE provides.

As a client, you could be making a decision about what is more likely:

    1.  The attacker is able to undermine some CA.

    2.  The attacker is actually on-path and going to undermine my
    connection.  

In many cases, one might decide that (1) is more likely than (2), and
therefore decide that TLSA is a better thing to rely on.  During
deployment, however, one might be willing to think that (1) is less
likely than, "I am in a coffee shop, and these people bought crappy
infrastructure."  In that case, one might want to be able to fall back
to the way we actually do this today.  

I imagine that, over time, the tolerance for the broken infrastructure
will go down, and the fall-back decision will be less and less
attractive.  But if the protocol says that once a client supports
TLSA, any not-fully-modern DNS environment just means "no TLS", then
we will be promulgating a standard that cannot be deployed.  We might
as well not publish it.

A

-- 
Andrew Sullivan
[e-mail]