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Re: [Dcrup] I-D Action: draft-ietf-dcrup-dkim-usage-02.txt

"Murray S. Kucherawy" <superuser@gmail.com> Mon, 12 June 2017 03:29 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Sun, 11 Jun 2017 20:28:56 -0700
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To: Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: [Dcrup] I-D Action: draft-ietf-dcrup-dkim-usage-02.txt
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On Sat, Jun 10, 2017 at 2:42 AM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> I find the construction of this draft strange.  Why not simply say
> "verifiers MUST implement and use rsa-sha256 instead of rsa-sha1"?
> The remainder of the text is largely unchanged, which took me a while
> to validate.
>
> The problem here is that removing the definition of rsa-sha1 is not
> the point.  The code point can't be undefined (Section 7 gets that
> right), and we don't really benefit from having the definition
> removed.  What we want is to have rsa-sha256 implemented and deployed.
>
> So say two things, just to be perfectly clear:
>
> 1. DKIM implementations MUST NOT rely on rsa-sha1, it's busted.
>
> 2. DKIM implementations MUST use rsa-sha256.  Signers MUST create
> signatures using rsa-sha256 and verifiers MUST verify those
> signatures.
>

That idea is fine with me.  Specifically, I think "MUST NOT rely on" is
better than "MUST NOT implement".

-MSK

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