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Re: [Cfrg] Help with the use of contexts

Yoav Nir <ynir.ietf@gmail.com> Tue, 17 January 2017 15:56 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Tue, 17 Jan 2017 17:56:06 +0200
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References: <20170116200948.6535.qmail@cr.yp.to> <5eeb3d4d-1fc0-35ba-6f47-87fa0d808edc@cs.tcd.ie>
To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Subject: Re: [Cfrg] Help with the use of contexts
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> On 17 Jan 2017, at 13:48, Stephen Farrell <stephen.farrell@cs.tcd.ie> wrote:
> 
> 
> 
> On 16/01/17 20:09, D. J. Bernstein wrote:
>> I would really like to see this unnecessary complexity eliminated from
>> CFRG's signature specifications.
> 
> I'm relatively neutral on the use or non-use of contexts,
> but lean more towards Dan's position that the API changes
> involved mean that practically, it's better to not demand
> contexts.

Me too.

> However, I really do wish that CFRG specs would not offer
> both choices - that will simply lead to repeating this
> discussion each time an IETF protocol wants to use the CFRG
> spec. And of course, different decisions will be made over
> time,

Not over time. In the next few months the IESG is going to get documents about EdDSA signatures from TLS, IPsecME and curdle for signatures in TLS, IKE, and PKIX respectively.  If the decision is not the same in all of them, I think (hope) that the IESG would ask why.

> leading to slightly more mess than would otherwise
> exist. That's not a showstopper thing, but life will be
> better if the choice is not offered.
> 
> So, I'd support eliminating contexts from CFRG specs and
> saying something like "if you want that, and it's not a
> bad idea for avoiding cross-protocol attacks, then do it
> at a layer above the crypto API."
> 
> Cheers,
> S.
> 
> PS: random idea - I wonder if analysis of wireshark
> dissector source code, or some application calling
> such code, might be a fine way to spot potential
> cross-protocol attacks - anyone know if that's been
> tried?
> 
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