It appears that Phillip Tao  <[email protected]> said:
>1. Easier to implement - By sharing much of the underlying technology with a 
>widely deployed (or rather,
>hopefully-soon-to-be-widely-deployed) authentication mechanism in DKIM2, it 
>will be easier for both senders and receivers to adopt.
>Similarly, implementors do not have to worry about cases like the inner 
>headers not matching outer headers.

But, as I explained in the previous message, there is nothing to share.  The
headers for the unobtrusive signatures are inside a MIME part so they're inside 
the
message body and do not get canonicalized by DKIM.

>2. Explicit compatibility with DKIM2 - Ideally, these signatures should not be 
>broken by intermediate hops that conform to DKIM2's
>diff algebra. By explicitly sharing the same canonicalization and signing 
>scheme as DKIM2, this would guarantee compatibility with the
>DKIM2 ecosystem.

But the signatures are on a message mapped in a MIME part which will either be 
there
or it won't.  It is hard to imagine a realistic situation where there would be a
change described by diff algebra that would affect the insides of the signed 
MIME part.

>3. No MIME structure alteration - These signatures are meant to be 
>"unobtrusive". Part of that to, IMO, is that there's absolutely no
>impact on how the message is treated by the receiving MTA and MUA, regardless 
>of the MUA's support for this scheme. From the
>draft/DKG's presentation in Madrid, it seems like this draft has been fairly 
>well tested already, and seems compatible. However, it's
>obviously infeasible to test all existing MUAs, not to mention future versions 
>of MUAs. There's significantly less risk of errant MUA
>behavior if the actual message body does not need to have a different MIME 
>structure to support this signature scheme. This also
>simplifies interaction with things like Structured Email, in which certain 
>MIME structures signal certain cases.

DKIM is, at least at the moment, oblivious to MIME.  We've had some thoughts 
about
signing MIME parts separately, but I still don't think that matters here since 
the
DKIM2 signatures would be unrelated to the PGP signatures you're using.

>DKIM signatures can sign other headers. For DKIM2, I believe there's a 
>proposal to just always sign all headers.

Perhaps, but since the headers you care about are inside a MIME part, it's 
irrelevant.

I am not opposed do doing things in a common way where it makes sense, but I 
still do not see how these MIME
wrapped PGP signatures are like DKIM signatures other than that they use the 
word "signature".

R's,
John

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