[Dcrup] Re: [standards] [Editorial Errata Reported] RFC8463 (7930)

Steffen Nurpmeso <steffen@sdaoden.eu> Sun, 12 May 2024 00:53 UTC

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Date: Sun, 12 May 2024 02:52:58 +0200
Author: Steffen Nurpmeso <steffen@sdaoden.eu>
From: Steffen Nurpmeso <steffen@sdaoden.eu>
To: Viktor Dukhovni <viktor@dukhovni.org>
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Subject: [Dcrup] Re: [standards] [Editorial Errata Reported] RFC8463 (7930)
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Viktor Dukhovni wrote in
 <ZkAOictS1ygyIBZe@chardros.imrryr.org>:
 |On Sat, May 11, 2024 at 10:10:39PM +0200, Steffen Nurpmeso wrote:
 |> Thanks a lot for spending so much time and effort to figure out
 |> John R's fault, your crypto knowledge and artistic is always
 |> amazing to read *and see*.  Thank you!
 |
 |I believe you owe an apology to John Levine, and more generally would

I apologise to John R Levine for the tone.

 |achieve better results by practicing some more humility.  Your current
 |flame thrower on full blast approach is not productive.

I cannot change my entire being though.

 |>|3. This is then signed with the Ed25519 key from RFC8032:
 |>  ...
 |> 
 |> Wonderful, thank you very much.  So John R Levine mapped the RSA
 |> scheme onto Ed25519, where one first generates a message digest,
 |> which is then signed.
 |
 |No.  You've failed to read the DKIM RFCs.  All DKIM signatures

No i did not.
We have two hashes, one for the body, and one for the
canonicalized headers.

  ...
 |Please resist any temptation to signal indignation, this matter should

With RFC 8463 we have three.
Because the algorithm as such performs hashing itself.

Sure, SHA-512 is likely more expensive than SHA-256, it would
require tests to know how much that matters given how expensive
the modern algorithms are.  That is to say, wether doing SHA-256
on the to-be-signed-headers and then RFC 8032 on the signature is
less expensive than simply passing the readily prepared headers to
the algorithm which performs digesting itself.

 |now be closed.  Your Ed25519 signing implementation needs to hash the
 |message, and then sign the hash.

I want to point out that this requires extra code in most
implementations.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)