Re: [TLS] draft-ietf-tls-curve25519-01: Is public key validation necessary or helpful?

Ilari Liusvaara <ilariliusvaara@welho.com> Wed, 30 December 2015 11:10 UTC

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Date: Wed, 30 Dec 2015 13:10:51 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Brian Smith <brian@briansmith.org>
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Subject: Re: [TLS] draft-ietf-tls-curve25519-01: Is public key validation necessary or helpful?
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On Tue, Dec 29, 2015 at 09:05:17AM -1000, Brian Smith wrote:
> On Tue, Dec 22, 2015 at 2:09 PM, Brian Smith <brian@briansmith.org> wrote:
> 
> > If an implementation only implements ECDHE cipher suites then
> > implementing the session hash extension is not necessary, according to RFC
> > 7627. I believe there are also a few other factors that would implementing
> > the session hash extension to be unnecessary.
> >
> > If checking that the shared value isn't zero is sufficient, and/or
> > blacklisting the public values that DJB mentions in [1] is sufficient,
> > either would be better than mandating the implementation of the session
> > hash extension just for this purpose.
> >
> 
> Actually, the check for a result of zero is already required in the current
> CFRG draft; see [1]. So, I think that the easiest way to fix the TLS draft
> is to just delete the misleading text.

The RFC4492bis draft already species that peer must abort on zero output.


-Ilari