Re: [dane] Digest Algorithm Agility discussion

Peter Palfrader <peter@palfrader.org> Sat, 22 March 2014 07:47 UTC

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Date: Sat, 22 Mar 2014 08:47:37 +0100
From: Peter Palfrader <peter@palfrader.org>
To: dane@ietf.org
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References: <20140315051704.GY21390@mournblade.imrryr.org> <0l4n2sa5a0.fsf@wjh.hardakers.net>
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Subject: Re: [dane] Digest Algorithm Agility discussion
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On Thu, 20 Mar 2014, Wes Hardaker wrote:

>    Do you, Mr. System Administrator defining the local policy for the
>    *client*, want:
> 
>    A) Accept any published hashing algorithm out of my "unordered set"
>       to validate the remotely presented certificate.  [Ordering it
>       doesn't buy you anything since you'll simply accept a match and it
>       doesn't matter which you try first, since any success in any
>       algorithm will equally indicate "ok"; in fact in an implementation
>       aiming for speed, it might be best to choose the order based on
>       how fast you can execute the algorithm].  If the server fails to
>       publish a perfect record set, as long as one matches I'm ok with that.
> 
>    B) Believe that the server will always publish perfect records, and
>       if my "ordered set" of algorithms is [SHA512, SHA256] and they
>       publish SHA512, then I never want to accept SHA256 because I fear
>       an attack more than I fear a server administrator blowing their
>       configuration.

> But the real question, is what is the *default* that we should suggest
> an implementation do?

> II) what should we do in SMTP?  This is where Viktor, considering case
>     #2 above, is wanting to do B ("accept just the 'best' in an ordered set
>     of algorithms) instead of A.  The arguments, though, from both sides
>     are probably talking about different cases (generic vs SMTP) and I
>     think that is ending up with some of the confusion.

I'd like to see the SMTP draft suggest B.  (All the others should do B
too, but that's a different story).

Aloha,
-- 
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