Re: [DNSOP] [Technical Errata Reported] RFC8078 (5049)

Dick Franks <rwfranks@acm.org> Mon, 26 June 2017 11:30 UTC

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From: Dick Franks <rwfranks@acm.org>
Date: Mon, 26 Jun 2017 12:29:57 +0100
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To: Matthijs Mekking <matthijs@pletterpet.nl>
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Subject: Re: [DNSOP] [Technical Errata Reported] RFC8078 (5049)
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On 26 June 2017 at 09:39, Matthijs Mekking <matthijs@pletterpet.nl> wrote:

I raised the specific issue because the to be RFC 8078 was going to change
> the CDS and CDNSKEY RDATA format from a fixed length RDATA to a variable
> length: In case of the DELETE operation, the Digest in presentation format
> was omitted.
>

CDS and CDNSKEY are both variable length. There is no length component in
the RDATA itself. The length of the digest (or key) is calculated (RDLENGTH
- 4) so whether there is one byte or none at all makes not a scrap of
difference. So that explanation can be dismissed immediately.


While I agree with Paul in that thread that we should use all zeros for the
> DELETE operation, I believe it was an oversight that the proper encodings
> (hexadecimal, base64) should be used.
>

Not just an oversight. Now it is an oversight baked into an IESG approved
standards track document.

So an implementer has little choice but to make CDS/CDNSKEY work in
accordance with the standard as written until IESG approves something else.

And when that something else arrives, users will be mightily upset if
RFC8078 CDS/CDNSKEY suddenly stops working, so the code will need to cope
with both versions.  The only realistic way to achieve that is to determine
the entire content of the DELETE CDS/CDNSKEY from the zero algorithm field.
Beyond that, the content of the "mandated notation" is irrelevant because
it can be left unparsed.