[ietf-dkim] Final update to 4871bis for working group review

[Charles Lindsey]

On Mon, 11 Jul 2011 05:53:58 +0100, Murray S. Kucherawy  
<msk at cloudmark.com> wrote:

> Actually, let me revise that a bit:
>
> "Agents that evaluate or apply DKIM output need to be aware that a DKIM  
> signer can sign messages that are malformed (e.g., violate RFC5322), or  
> become malformed in transit, or contain content that is not true or  
> valid.  Such an action might constitute an attack against a receiver,  
> especially where additional credence is incorrectly given to a signed  
> message without evaluation of the signer.  Moreover, an agent would be  
> incorrect to infer that all instances of a header field are signed just  
> because one is.  Agents will need to account for these issues when  
> deciding how to apply DKIM results to message, especially when  
> displaying them to users."

OK, there is much good stuff in that. In particular, it makes it clear  
that Bad Stuff can originate from the signer as well as from  
men-in-the-middle and replayers. But I am still concerned that multiple  
occurrences of "singleton" headers fields are not explicitly mentioned,  
even as just one possible example. So perhaps, just before the last  
sentence:

"... , in particular if that field was not supposed to occur more than  
once."

After all, you were seemingly happy to mention that particular trap in  
8.14 in draft-12.

Not sure about the word "incorrectly", but s/without evaluation/without  
adequate evaluation/ might make your point better. Though I expect, of the  
millions of perfectly legitimate domains that will exist without special  
recognition in any reputation system, it will be hard to spot a newly  
appearing 'badguy' one.

I still don't think that paragraph is what we really need, but I will  
withold judgement on that until I see how it gets incorporated into the  
other bits of text that are around.

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
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   Web: http://www.cs.man.ac.uk/~chl
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