Subject: RE: [ietf-dkim] Base issue: multiple linked signatures

From: "Hallam-Baker, Phillip" <[email-masked]>
Date: Thu, 4 Jan 2007 06:23:06 -0800

> [mailto:[email-masked]] On Behalf Of Charles Lindsey

> I just want to point out that similar arguments also apply to 
> the "MUST sign the From header" case.

I disagree, I can easily write a test vector for that MUST so it is emprically verifiable. Hence it can be made a MUST.

In general we can place MUSTs on senders but its much harder to do this on receivers. A Must on a receiver means 'if you do this and it breaks in future we will hang you out to dry if we choose unless you manage to make the practice so widespread that we cannot ignore it'.

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From: "Charles Lindsey" <[email-masked]>
Date: Thu, 04 Jan 2007 20:02:51 -0000

On Thu, 04 Jan 2007 14:23:06 -0000, Hallam-Baker, Phillip  
<[email-masked]> wrote:

> I disagree, I can easily write a test vector for that MUST so it is  
> emprically verifiable. Hence it can be made a MUST.

True. Perhaps I overstated my case. However, it still conflicts with RFC  
2119, since no interoperabilty arises (the sky does not fall in) if you  
fail to sign the From. All that happens is that people might suppose it is  
not always a good idea (and they m,ay even turn out to be right in some  
cases). But you are not supposed to use "MUST" for that. "SHOULD" would be  
quite strong enough.

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