On Friday, 16 September 2016 15:52:30 CEST Salz, Rich wrote:
> > The majority of servers (71%) support *only* prime256v1 curve and of the
> > ones that default to ECDHE key exchange nearly 83% will also default to
> > this curve.
> That's because most people have not moved to OpenSSL 1.1.0 yet.  I'm not
> joking, I think that's a major reason.
> > OpenSSL 1.0.2h also defaults to this curve if there are no curves
> > advertised by client.
> When I made X25519 the default, I didn't think about it.  That was probably
> a mistake.  Good catch!
> > So it is very likely that any client that doesn't advertise curves will
> > expect the server to select prime256v1. At the same time it is very
> > unlikely that it will support x25519 (given how new it is).
> Well the major browsers support it now, so once servers start upgrading to
> 1.1.0 it will be less of an issue.  But maybe the community thinks the
> current behavior is a bug?

if client advertised curves, and the curves include stuff besides prime256v1 I 
*expect* the other stuff to be negotiated, unless it's smaller than 256 bits, 
but it's not what I was talking about

I'm talking only about the case of "no curves advertised at all" i.e. 
supported_groups extension missing completely from client hello

Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 99/71, 612 45, Brno, Czech Republic

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