ietf-822
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Re: [ietf-822] A permission to re-sign header

2014-04-21 22:09:12
On Sat, Apr 19, 2014 at 09:05:23AM -0400, Michael Richardson wrote:

Yes, in particular, it's quite likely both DKIM and S/MIME signatures will
not survive some things the mailing list might want to do, including:

1) removing html parts or other attachments
2) formatting html part to text/plain
3) formatting text/plain; format=outlook into proper format=flowed


We may need to consider whether this is something that we have to give
up.  I'm not sure how important it is to allow mailing lists to remove
html parts, etc.  If mailing lists need to simply reject messages that
have html parts, there are mailing lists that do that already, just as
their are mailing lists that reject messages that dont' meet other
administrative prohibition --- such as the e-mail being too large, for
example.

There are mailing lists that want to "fix" broken messages, yes, but
if we need to provide end-to-end assurance that the message really
came from the originator, disallowing this behavior so that things
like S/MIME and PGP signatures don't get broken might be an
engineering tradeoff that we might have to make.

That's possible, but then you run into other problems. Take the issue
of adding a disclaimer. You can certainly do this without damaging
the S/MIME signature by converting a MIME structure of:

   multipart/signed
     text/html
     applciation/signature-whatever

to:

   multipart/mixed
     multipart/signed
       text/html
       applciation/signature-whatever
     text/plain - disclaimer

But then you have to take into account how this gets displayed, and what
it means when it is displayed.

And while you may be able to get lists to pass HTML through, reject messages
with attachments, and generally get to a place where S/MIME signatures can be
preserved, I don't think you'll be able to get rid of disclaimers.

                                Ned

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