Re: [TLS] SHA-3 in SignatureScheme

Hubert Kario <hkario@redhat.com> Fri, 02 September 2016 10:08 UTC

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From: Hubert Kario <hkario@redhat.com>
To: Dave Garrett <davemgarrett@gmail.com>
Date: Fri, 02 Sep 2016 12:08:47 +0200
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Subject: Re: [TLS] SHA-3 in SignatureScheme
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On Thursday, 1 September 2016 19:22:18 CEST Dave Garrett wrote:
> On Thursday, September 01, 2016 02:30:54 pm Scott Fluhrer (sfluhrer) wrote:
> > > On Thursday, 1 September 2016 12:43:31 CEST Benjamin Kaduk wrote:
> > > > On 09/01/2016 12:38 PM, Hubert Kario wrote:
> > > > > The SHA-3 standard is already published and accepted[1], shouldn't
> > > > > TLSv1.3 include signatures with those hashes then?
> > > > 
> > > > Why does it need to be part of the core spec instead of a separate
> > > 
> > > document?
> > > 
> > > because: we also are adding RSA-PSS to TLSv1.2 in this document, I don't
> > > see why it needs to be delayed. Finally, TLSv1.2 added SHA-2 just like
> > > that, it was not tacked on later.
> > 
> > IIRC, SHA-2 was a special case; SHA-1 was demonstrated to be
> > cryptographically weaker than expected and so we needed to have a secure
> > alternative ASAP.
> > 
> > The SHA-3 is not like that; there's no evidence that suggests that SHA-2
> > is weak; the only incentive to implementing SHA-3 is "we'll, it is a
> > standard, and so we might as well support it".
> The reason I see is that we currently specify exactly one valid hash
> algorithm (in a variety of sizes). The precedent argument is good enough
> for me. I think adding it in this document is definitely worth considering.
> I don't want to wait until SHA-2 is considered weak to provide an
> alternative, if we can avoid it.

I've created a PR for it: https://github.com/tlswg/tls13-spec/pull/616

I haven't changed any recommendations, the recommended hashes to implement are 
still SHA-2 based, and I don't think we should change that given that 
certificates just now are transitioning to SHA-256 because of incompatibility 
fears.

-- 
Regards,
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