Re: [TLS] Application data during renegotiation handshake

[David Benjamin <[e-mail]>]

On Wed, Nov 11, 2015 at 10:43 PM Yoav Nir <[e-mail]> wrote:

>
> > On 12 Nov 2015, at 3:32 AM, Adam Langley <[e-mail]> wrote:
> >
> > The TLS 1.3 post-handshake client-auth was intended, as I recall, to
> > support HTTP/1.1 over TLS 1.3.
>
> No, it was (and is) presented as a way to do client certificate
> authentication with HTTP/2 not at the initial handshake.
>
> > With HTTP/2 isn't it cleaner to do client-auth at the HTTP layer (i.e.
> > by signing exporter values)?
>
> It is. I thought that an HTTP authentication method based on certificates
> could be a drop-in replacement for TLS layer authentication, but someone (I
> think it was Mike) pointed out that with TLS-layer certificate
> authentication the stream continues after the authentication, while with
> HTTP-layer authentication, the stream ends with a 401 status code, and the
> client has to start a new stream with the Authorization header. So
> applications would need to be changed for this to work.
>

Using existing HTTP semantics would certainly be cleaner in a vacuum, but
one could still do it in HTTP/2 layer without creating a new stream.
Perhaps adapt SPDY's CREDENTIAL frame and add a new SWITCH_CREDENTIAL frame
to swap a stream's credential slot mid-stream?

Alternatively, HTTP/2 frontend could make the application think there were
two independent requests. Am I misunderstanding the objection? What about
this:
1. Client hits HTTP/2 frontend. Frontend talks to application which decides
it needs client auth, expecting it on the same stream.
2. Frontend immediately aborts that request and returns a 401 to the
client. Application thinks the client just gave up.
3. Client makes a new stream, now authenticated. The frontend hits the
application fresh. Application requests client auth as before and frontend
responds immediately with the certificate the client asserted.
This is, by the way, how Chrome implements client auth today, even with
renego. We never reconfigure client auth mid-stream.

I think it would be helpful to have examples of exactly what the
applications look like, to know what constraints the various interested
parties are working with.

For example, Apache httpd has some high-level configuration file.
https://httpd.apache.org/docs/2.2/ssl/ssl_howto.html#arbitraryclients
Existing Apache installs can easily compatibility regardless of how the
HTTP/TLS interaction looks.

On the other extreme, if the goal is to keep Apache httpd unchanged while
only changing OpenSSL, then we have a very different picture because the
OpenSSL API is SSL_renegotiate/SSL_do_handshake (send a HelloRequest) +
SSL_set_state/SSL_do_handshake (don't continue until renego completes).
That one is quite overfit to the old flow and will be difficult to
reconcile with almost anything.

draft-thomson-http2-client-certs-00's HTTP/2 mode seems to be targeting
something in between. It's okay with adding a new application_context_id,
but the client certificate still needs to be asserted at the transport. I'm
having a hard time divining the constraints from this.

David