Re: [TLS] A la carte handshake negotiation

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Mon, 29 June 2015 09:06 UTC

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Date: Mon, 29 Jun 2015 12:06:04 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
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Subject: Re: [TLS] A la carte handshake negotiation
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On Mon, Jun 29, 2015 at 08:58:11AM +0000, Peter Gutmann wrote:
> Nico Williams <nico@cryptonector.com>; writes:
> >On Sun, Jun 28, 2015 at 10:44:03AM +0300, Ilari Liusvaara wrote:
> >
> >>"Chinese menus" with coupled choices are classical source of interop
> >>problems.
> >
> >It's worked for SSHv2.
> 
> It worked for SSH because implementations use algorithm groups in highly
> stereotyped ways, so you have a de facto interop profile. Try negotiating
> e.g. RC4+SHA in one direction and AES+SHA2 in the other and see how quickly
> the wheels fall off.

Also, regarding kex+auth in SSH2, the authentication is interactive, so
choosing something bad most likely just gives an error and client trying
something else. Definitely not the case in TLS.

And record protections in different directions aren't even coupled choice
(all pairs should technically work).


-Ilari