Re: [TLS] Updating for non-X.509 certificate types

Eric Rescorla <ekr@rtfm.com> Fri, 10 March 2017 16:43 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 10 Mar 2017 08:42:38 -0800
Message-ID: <CABcZeBPeRYSVOXRm4rReQ-f3E1giJYiVgwJ4PmEOP7zaiZiRdQ@mail.gmail.com>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
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Subject: Re: [TLS] Updating for non-X.509 certificate types
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On Fri, Mar 10, 2017 at 8:37 AM, Ilari Liusvaara <ilariliusvaara@welho.com>
wrote:

> On Fri, Mar 10, 2017 at 07:02:22AM -0800, Eric Rescorla wrote:
> > On Fri, Mar 10, 2017 at 4:40 AM, Ilari Liusvaara <
> ilariliusvaara@welho.com>
> > wrote:
> >
> > > - user_mapping: Has extra handshake message.
> > > - cert_type: All the problems of CCertT and SCertT, combined with
> > >   fixing both to be the same.
> > >
> >
> > Does anyone use this?
>
> I don't think anyone uses it. cert_type was defined in order to use
> OpenPGP certs (RPK has SCertT and CCertT, altough in theory one could
> use cert_type). Nobody uses OpenPGP. Even the most notable TLS library
> supporting those (GnuTLS) is deprecating it.
>
> > > With user_mapping, applying similar trick as in status_request is
> > > not completely trivial because extensions that are answered in client
> > > Certificate are offered in CertificateRequest. Okay, except that
> > > extension is not an answer to ClientHello extensions, and the
> > > extension assumes offer-answer relationship between client and server
> > > extensions. Might need some special-casing.
> >
> > Yeah, I think we should probably just consider banning user_mapping,
> > at least until someone comes up with a way to use it here.
>
> IIRC, you asked "does anyone use this" before and some MS guys said
> yes, they use it.
>
> Or at least I remember some guys saying that they use it.
>
> > Could be useful to have explicit list of extensions (no registry, since
> > > this list can be never updated) that lists extensions that are
> > > deprecated in TLS 1.3.
> > >
> >
> > Currently this is by exclusion. I.e., these aren't listed as usable with
> > 1.3. It does seem to me that we shouldn't ban cached_info and
> > the cert type ones, because if/when they become usable with 1.3
> > then they should be permissible. So I think I would rather say
> > "don't advertise these with 1.3 unless you're willing to do them
> > with 1.3"
>
> The problem here is, one can't do that with TLS 1.2+1.3 dual-version
> either. If client doesn't know what extension X means in TLS 1.3
> (but does know it for TLS 1.2), if it advertises it, it runs the
> risk that server does in fact know what X does in TLS 1.3, and then
> blows up when server acts accordingly.
>

Right. I am saying that you must not offer these and 1.3 simultaneously
unless you implement whatever 1.3 thingy we finally define for it.

-Ekr


>
>
> -Ilari
>
>
>