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

Martin Thomson <martin.thomson@gmail.com> Mon, 12 June 2017 07:20 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Mon, 12 Jun 2017 08:20:18 +0100
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To: "Murray S. Kucherawy" <superuser@gmail.com>
Cc: Scott Kitterman <sklist@kitterman.com>, dcrup@ietf.org
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Subject: Re: [Dcrup] I-D Action: draft-ietf-dcrup-dkim-usage-02.txt
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On 12 June 2017 at 04:25, Murray S. Kucherawy <superuser@gmail.com> wrote:
> On Sun, Jun 11, 2017 at 1:40 AM, Martin Thomson <martin.thomson@gmail.com>
> wrote:
>>
>> https://github.com/kitterma/draft-ietf-dcrup-dkim-usage/pull/1
>>
>> I think that I got the essence of your changes there.  And it's a lot
>> shorter.
>
>
> Can you explain what you mean by "rely on"?

Sure, that's probably a bit of an imprecise way of saying that a
verifier needs to insist on receiving a valid rsa-sha256 signature and
that it can't just fall back to rsa-sha1.

> So by that logic, you can put a 1156-bit key in a record now without
> changing anything.  For anything bigger you will need multiple
> character-strings in the TXT field which I believe is one of the things John
> says doesn't fly in current provisioning software.

1156 is better, but I was hoping for a bit higher than that.  I would
include text that suggests this (explaining the limitations you set
out regarding the whitespace and so forth), but note that the
additional security margin is, well, marginal.

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