On Mon, May 2, 2016 at 12:55 AM, Viktor Dukhovni <[email protected]>
wrote:

>
> > On May 1, 2016, at 5:00 PM, John Levine <[email protected]> wrote:
> >
> >> So using the domain as-is and dealing with any provisioning politics
> >> looks to be the only sensible option.
> >
> > Not to put Daniel on the spot, but since he happens to work for one of
> > the largest mail providers in the world, would it be a problem to put
> > the STS stuff at URLs like these?
> >
> > https://google.com/.well-known/sts-policy
> > https://gmail.com/.well-known/sts-policy
> >
> > My impression from the converstation in B.A. was that it'd be
> > a big problem.
>


Probably the most likely answer is that it would be easier than deploying
DNSSEC and harder than deploying at a custom host. For us it's probably
doable; for some organizations I would imagine it to be substantially
harder (if, for example, their  email domain doesn't have an HTTPS presence
today).



> We need to put the organizations behind this draft on the spot to
> not shirk this issue.  There's no free lunch.  I think it is fair
> to ask the email folks at the large providers to negotiate with
> others in their organization to deploy this in a manner that results
> in a simpler security model.
>
> SRV is very much not "webby".  HTTPS libraries don't do SRV lookups,
> or else when asked to connect to a hostname resolved via SRV outside
> the library, will authenticate the insecurely obtained target name.
>

Just to be clear, your point is not really that doing SRV or TXT resolution
of the policy server's hostname is a problem; it's that short of overriding
some HTTPS library's certificate matching, we would be potentially matching
a cert for (say) "sts_policy.example.com", which removes some of the
intended guarantees of "certificate matches the email domain," right?


>
> So either the above ".well-known", or a kludgey reserved hostname
> prefix, but there's no precedent for such reservations.
>
> --
>         Viktor.
>
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