In message <[email protected]>, Viktor Dukhovni writ
es:
> On Sun, Mar 23, 2014 at 09:00:08PM +0100, Peter Palfrader wrote:
>
> > On Mon, 24 Mar 2014, Mark Andrews wrote:
> >
> > > > Site A only publishes SHA1 entries. Would rather do unauthenticated TL
> S
> > > > than trust SHA1?
> > >
> > > You left out - report and refuse to send until fixed.
> >
> > No, that's not what the SMTP draft suggests. When DANE is not there,
> > then servers just fall back to not authenticating a peer's cert, as they
> > do nowadays.
The SMTP draft says how to securely go from a email domain to a
CERT using DNSSEC and TLSA. It does not say whether one should use
a non secure connection or not. That is seperate policy.
> Indeed if one simply considers (again hypothetically) SHA1 to be
> "unusable", then with no "usable" TLSA records, the connection
> would fall back to unauthenticated TLS.
It might or it might not. That is a seperate policy decision.
> To do what Mark suggests, we'd have to treat SHA1 as usable, but
> always fails. That is new code to make SHA1 never match.
One will have something like
if (!supported(match))
skip record;
> And
> still I don't see anyone shooting themselves in the foot with
> self-imposed flag days for a long time after an algorithm becomes
> suspect.
>
> I sees that, the unstated objection must be a belief that SHA2-256
> will never fail, and thus we're wasting time designing solutions
> to a non-problem. While I don't believe in eternal unbounded
> progress, and (barring a P=NP revolution) it is likely that at some
> point we'll have algorithms that never need replacement, it is
> perhaps premature to declare mission-complete with SHA2.
I don't assume that it will never be broken. I also don't think we
need to "if has_alg(a) then {} else {}".
> For if we are to take the threat of gradual degradation of our
> confidence in SHA2 seriously, we need usable approaches for phasing
> it out. Flag days don't look like usable approaches to me.
>
> --
> Viktor.
>
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--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [email protected]
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