Re: [TLS] Options for negotiating hybrid key exchanges for postquantum

Stephen Farrell <stephen.farrell@cs.tcd.ie> Tue, 30 July 2019 19:53 UTC

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To: "Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com>, Watson Ladd <watsonbladd@gmail.com>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Tue, 30 Jul 2019 20:52:56 +0100
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Subject: Re: [TLS] Options for negotiating hybrid key exchanges for postquantum
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I'm neutral as to how we represent this stuff for the moment
as I think it's too early to tell until we get closer to the
end of the algorithms competition.

That said, I do want to second this...

On 30/07/2019 19:41, Scott Fluhrer (sfluhrer) wrote:
> Here is one opinion (mine, but I'm pretty sure it is shared by
> others): the various NIST candidates are based on hard problems that
> were only recently studied (e.g. supersingular isogenies, Quasicyclic
> codes), or have cryptanalytic methods that are quite difficult to
> fully assess (e.g. Lattices).  Even after NIST and CFRG have blessed
> one or more of them, it would seem reasonable to me that we wouldn't
> want to place all our security eggs in that one basket.  We currently
> place all our trust in DH or ECDH; however those have been studied
> for 30+ years - we are not there yet for most of the postquantum
> algorithms.
> 
> Hence, it seems reasonable to me that we give users the option of
> being able to rely on multiple methods.
The only person with whom I've spoken who said he'd plan to
deploy some of this soon is a VPN operator who explicitly
wanted to start early and use >1 PQ scheme (3-4 is what he
said) plus a current scheme. His expectation was that that'd
settle down to one PQ scheme, or one PQ and a current one,
in time, but that time may be a decade after he'd like to
start.

So, to the extent it matters, count me as a +1 for supporting
that.

Cheers,
S.