Re: [TLS] Closing on 0-RTT

[Colm MacCárthaigh <[e-mail]>]

On Mon, Jun 12, 2017 at 11:19 AM, Salz, Rich <[e-mail]> wrote:

> I agree with this.  Which is why I prefer separate streams for early data,
> and some kind of signaling to the content provider that is clear and
> unambiguous.  I don't know how to do that when, say, the intermediary/CDN
> has a persistent connection to the backend...
>

I've given this some thought, and I think it might be unworkable to have
some kind of end-to-end 0-RTT. A simple example is that a CDN might want to
make a slightly different request, with extra headers, towards the origin
than the request that came in from the browser. For instance, the CDN might
add an If-None-Match: or an If-Modified-Since. But those may not fit within
the 0-RTT size limit.

It gets really complicated across layering boundaries to have the CDN only
accept 0-RTT if the origin also does, and if the request towards the origin
will also fit, and so on. I think the CDN would have to defer accepting the
0-RTT from the browser until the origin accepted the 0-RTT from the origin;
which defeats a lot of the intended speed/throughput benefit.

Through this I've come to the conclusion that separate streams create more
problems than they solve, and robust replay mitigation is a better answer.

-- 
Colm