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Re: [openpgp] MIME signature impact

2015-04-07 12:36:12
On Tue 2015-04-07 09:02:29 -0400, Phillip Hallam-Baker wrote:
If we are doing an overhaul of PGP, one of the things that needs
fixing is a way to send signed messages that does not get in the way.

I think you're saying we need to figure out how to make cleartext
signatures that can live somewhere that non-compatible mail user agents
won't show them to the (presumably confused) user.

(this is not at all about encrypted+signed messages, right?  I'll leave
those for a separate discussion)

[ i also think this might not be in-scope for the revised OpenPGP
  working group if we're just going to work on 4880bis -- it could be
  relevant for CMS messages as well, and maybe we should find some other
  place to have this discussion.  that said, more clarifications below ]

I agree with you that securing only the text part (and not even the
character encoding) of an e-mail message is insufficient today.

It also sounds to me like you think that PGP/MIME clearsigned messages
do "get in the way".  In particular, confused MUAs will present them as
attachments that confused users then try to download and "open", and
they "don't work".

Is that right?

Placing the signature in the message header is problematic when any
intermediary modifies the content of a message.  RFC 2015 makes it quite
clear that multipart/signed message parts should be treated as bytewise
opaque -- mail transfer agents should not modify them.  Moving the
signature to the header and leaving the rest of the message undecorated
seems likely to encourage in MTAs the temptation to fiddle with the
content.  The more that message signatures fail due to MTA fiddling, the
more users will become careless about bad-signature alerts, so i think
that's a pretty risky outcome.

Do you see some way that we can effectively signal the need for message
(or message-part) opacity to MTAs while not causing UI/UX confusion for
users trapped on ignorant MUAs?

        --dkg

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