[exim] Re: List headers [Was: DKIM does not work]

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Autor: Markus Reschke
Data:  
Para: Ian Z via Exim-users
Asunto: [exim] Re: List headers [Was: DKIM does not work]
Hi!

On Mon, 23 Oct 2023, Ian Z via Exim-users wrote:

> On Mon, Oct 23, 2023 at 11:51:21AM +0200, Andreas Metzler via Exim-users wrote:


>> Kind of. The RFC has big fat disclaimer that it only provides very
>> rough guidance ("The choice of which header fields to sign is
>> non-obvious.") and is very very thin on details, afaict it does not
>> say a thing about oversigning.
>
> Right, in the sub-section cites it says (lightly paraphrased):
>
> The following headers SHOULD be signed *if they are present* in the
> message.
>
> Emph mine. So, like Andreas writes, if they are *not* present, this is
> vacuous.


When you check out the h tag of the DKIM signature header of the large
email services you'll see that they usually have only a few signed headers
(less processing load) and some oversign specific headers. E.g. gmail
seems to oversign from:to:cc:subject:date:message-id:reply-to, and Yahoo
From:Subject:Reply-To. Based on the DKIM RFCs and the current reality I'd
say that exim's default for dkim_sign_headers is simply overkill and we
should add a bunch of '=' prefixes, maybe a few '+' for essential headers.

ciao
  Markus
-- 
/ Markus Reschke              \
\ madires@??? /



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