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Re: [dmarc-ietf] ARC Crypto Algorithm Selection

"Kurt Andersen (b)" <kboth@drkurt.com> Tue, 23 October 2018 15:24 UTC

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From: "Kurt Andersen (b)" <kboth@drkurt.com>
Date: Tue, 23 Oct 2018 08:24:13 -0700
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To: Scott Kitterman <sklist@kitterman.com>
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Subject: Re: [dmarc-ietf] ARC Crypto Algorithm Selection
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On Tue, Oct 23, 2018 at 3:58 AM Scott Kitterman <sklist@kitterman.com>
wrote:

> Last time I looked at this particular issue, ARC could use any algorithm
> that
> DKIM uses.


Still correct.


>   As I recall, that was once of the stimuli for the DCRUP working
> group (to avoid having rsa-sha1 be valid for ARC by obsoleting it in DKIM).
>

I don't think that ARC drove the DCRUP work as much as the desire to get
badness officially obsoleted :-)


> It looks like this discussion has been moved to a new draft,
> https://tools.ietf.org/html/draft-ietf-dmarc-arc-multi-01 (although the
> reference is wrong,
> https://tools.ietf.org/html/draft-ietf-dmarc-arc-multi-02
> is current.
>

Yes that's correct.


> Unfortunately, I don't find any actual guidance on what algorithms are
> currently used.


Any that are valid for DKIM - see first sentence above.


> Secion 6, Phases of Algorithm Evolution, gives some process
> (which seriously needs revision - I thought we all knew flag days don't
> work
> at Internet scale), but no actual guidance.
>

Correct - we've deferred any real attention on this until we got the ARC
protocol document nailed down. With the request to publish being a few
hours old now from Barry, this might be an excellent topic to pursue next
:-)


> DKIM, as updated by the DCRUP work, has two valid crypto algorithms:
>
> rsa-sha256
> ed25119-sha256
>
> One has been obsoleted:
>
> rsa-sha1
>
> Which among those is valid for ARC and how do I know?
>

The same ones that are valid for DKIM (as updated by DCRUP). What we
haven't worked out is how to handle mixed algorithm chains.

--Kurt

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