Re: [tcpinc] tcpcrypt MTI key exchange (speak now or forever hold your peace...)

iang <iang@iang.org> Tue, 24 October 2017 10:41 UTC

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To: David Mazieres expires 2018-01-21 PST <mazieres-m3w8362yb4cc5hherzqjdkknf6@temporary-address.scs.stanford.edu>, Gregorio Guidi <greg_g@posteo.net>, tcpinc@ietf.org
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From: iang <iang@iang.org>
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Date: Tue, 24 Oct 2017 12:41:51 +0200
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Subject: Re: [tcpinc] tcpcrypt MTI key exchange (speak now or forever hold your peace...)
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On 23/10/2017 22:25, David Mazieres wrote:

> We are considering the following proposal for MTI key exchange protocols
> in tcpcrypt:
>
>    1. Implementations MUST support Curve25519.
>
>    2. Implementations SHOULD support Curve448 to the extent that suitable
>       implementations are available.
>
>    3. Implementations MAY support P256 and P521 (particularly since
>       hardware implementations are widely available for the former).
>
> (Obviously whatever algorithms are supported can always be disabled by
> configuration--this is just about what the software MUST support, not
> what everyone must use.)
>
> The security ADs have not 100% signed off on this approach yet, but seem
> receptive to it.  However, given the timeline, we would like to
> parallelize things and find out *now* if there are any objections to the
> proposal.  Based on the working group discussion, I think everyone will
> be happy, so please speak up now if you object.
>
> Thanks,
> David

In general +1.

The only quibble I would have is that 2. Curve448 should be a MAY. 
Firstly, a caveated SHOULD becomes a MAY, at some level of 
approximation.  Secondly, if we manage to convince an enemy to crunch 
Curve25519 then we have won a great victory, and we can upgrade at our 
leisure with newer information.

But it is only a quibble - I wouldn't hold up any vote on this just 
because of an idle bar prediction on consequences.

iang