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

[Martin Rex <[e-mail]>]

Eric Rescorla wrote:
> 
> > If an application has any indication that TLSA is in use (such as
> > through a configuration setting), that application MUST not start a TLS
> > connection or abort a TLS handshake if either of the two criteria above are
> > not met.
> 
> I feel like this is confusing. There are two senses in which TLSA might
> be "in use". (1) The application is trying to retrieve it. (2) The DNS server
> is serving it. We're clearly in the first case, and it's the second which
> is unknown to us b/c under control of the attacker. Perhaps you
> mean to say "Applicaions SHOULD offer a setting to allow users to
> set strict TLSA checking, in which case..."

Similar to OCSP, any hard-fail requirement is going to create a
significant usability issue, and at worst, cause users to fallback
from a HTTPS-but-not-DANE-verifiable URL for a login page to
a plain HTTP login page -- which is making things *MUCH* worse.

I do not believe in DANE hard-fail without a DNSSEC records stapling
TLS extension (similar to the OCSP stapling TLS extension).
 
And as a fallback, browsers could use a TLSA & server-cert lock, i.e.
memorizing information from the last visit of a site and using that
to perform server endpoint identification in case that DNSSEC lookups
fail when roaming.


-Martin