Re: [Dcrup] combo update draft-ietf-dcrup-dkim-crypto-01

"John R Levine" <johnl@taugh.com> Mon, 12 June 2017 15:07 UTC

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Date: Mon, 12 Jun 2017 16:07:05 +0100
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From: John R Levine <johnl@taugh.com>
To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [Dcrup] combo update draft-ietf-dcrup-dkim-crypto-01
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> Quick comments:
>
>       sig-a-tag-k = "rsa" / "rsafp" / "eddsa" / "eddsafp" x-sig-a-tag-k
>
> This is missing a '/' for the extension piece.  Also, I would instead do:

It's supposed to replace the existing sig-a-tag-k and key-k-tag-type 
rules, not add new ones.  The explanatory wording could use some work.

> 1. You need to explicitly state that the hash function for the
> signature scheme is used to construct the fingerprint.

Here's what it says now.  This seems reasonably clear.

 	The DNS record contains a sha-256 hash of the public key, stored
         in base64 in the p= tag.  The key type tag MUST be present and
 	contains k=rsafp or k=ecdhfp.

I suppose I could change that to say use the hash of the signing algorithm 
if people think that's a good idea, but if we add algorithms that use 
hashes other than sha-256, we'll need another update anyway.

> 2. You need to explain how to validate a signature.

OK.

> This description could be made generic so that (for example) PQ
> schemes could use this.

No, my goal is to make the minimum changes needed.  The more options, the 
more chances not to interoperate.

R's,
John